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<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
<title><![CDATA[Ghost in the JVM]]></title>
<link href="http://dmly.github.io/atom.xml" rel="self"/>
<link href="http://dmly.github.io/"/>
<updated>2014-08-04T22:37:40+00:00</updated>
<id>http://dmly.github.io/</id>
<author>
<name><![CDATA[Doug Ly]]></name>
</author>
<generator uri="http://octopress.org/">Octopress</generator>
<entry>
<title type="html"><![CDATA[DIY Java App Server on OpenShift: So Far So Good]]></title>
<link href="http://dmly.github.io/blog/2013/05/01/diy-java-app-server-on-openshift-so-far-so-good/"/>
<updated>2013-05-01T14:36:00+00:00</updated>
<id>http://dmly.github.io/blog/2013/05/01/diy-java-app-server-on-openshift-so-far-so-good</id>
<content type="html"><![CDATA[<p>I have been playing with <a href="https://www.openshift.com/">RedHat OpenShift</a> platform for several days. So far the experience has been very good. Several nuances encountered but I was able to get my java server application
running in less than an hour. My application is not using any preconfigured OpenShift’s cartridge or application server as I know.
My application is a simple Gomoku game with WebSocket support. I use DropWizard as the light-weight server to bootstrap an embedded version of Jetty. Most of the issues I encounter were just
network interface permission, build, deploy and starting the app.</p>
<!-- more -->
<p>OpenShift comes with several preconfigured deployment platforms which they call cartridges. There are cartrige for Java app servers (JBoss, Tomcat), Python (Django) or Ruby on Rails.
Instead of deploying my <a href="https://gomoku-dmly.rhcloud.com/index.html">Gomoku</a> app, I just use the bare-bone DIY OpenShift virtual machine. To my surprise the DIY version of OpenShift already comes with JDK 7 (OpenJDK), Maven 3 and Ant 1.8
pre-installed. That saves me a tons of time. Since my Gomoku app is just a regular Maven project that uses <a href="http://dropwizard.codahale.com/">Dropwizard</a> all I need to do is to push my code into the RedHat OpenShift git repository (resides
inside my VM) to build and deploy the app.</p>
<p>There are some procedures I need to follow to make sure my app can run on OpenShift.
First, if the app needs to open a socket connection, I need to make sure that it binds on the permitted IP address. This is defined as $OPENSHIFT_INTERNAL_IP and the only allowed port is
8080. In Dropwizard I can easily configure that in the http session:</p>
<figure class='code'><figcaption><span>Dropwizard connection settings</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
</pre></td><td class='code'><pre><code class='yaml'><span class='line'><span class="l-Scalar-Plain">http</span><span class="p-Indicator">:</span>
</span><span class='line'> <span class="l-Scalar-Plain">bindHost</span><span class="p-Indicator">:</span> <span class="err">@</span><span class="l-Scalar-Plain">OPENSHIFT_INTERNAL_IP@</span>
</span><span class='line'> <span class="l-Scalar-Plain">adminPort</span><span class="p-Indicator">:</span> <span class="l-Scalar-Plain">8080</span>
</span></code></pre></td></tr></table></div></figure>
<p>You need to make sure your deploy script (more below) replace the @OPENSHIFT_INTERNAL_IP@ with the actual permitted IP address. You also want to make sure that the adminPort is the same 8080 as the app server port.
OpenShift free tier only allows one port 8080 open as far as I know.</p>
<p>Second, OpenShift has several activation hooks to automate things when you push commits to git. There are hooks for start, stop, deploy and build the app.</p>
<p>For my application, the build hook is just to build using Maven.</p>
<figure class='code'><figcaption><span>build</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class='bash'><span class='line'><span class="nb">cd</span> <span class="nv">$OPENSHIFT_REPO_DIR</span>
</span><span class='line'>mvn package
</span></code></pre></td></tr></table></div></figure>
<p>After the build, the deploy hook is called. My deploy script is to replace the @OPENSHIFT_INTERNAL_IP@ string with real permitted IP to bind to in the app config file.</p>
<figure class='code'><figcaption><span>deploy</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class='bash'><span class='line'><span class="nb">cd</span> <span class="nv">$OPENSHIFT_REPO_DIR</span>
</span><span class='line'>sed -i <span class="s1">'s/@OPENSHIFT_INTERNAL_IP@/'</span><span class="s2">"$OPENSHIFT_INTERNAL_IP"</span><span class="s1">'/g'</span> gomoku.yml
</span></code></pre></td></tr></table></div></figure>
<p>Finally, the start hook is called. This time I just run the JVM with my jar file. Dropwizard does a great job making this so easy.</p>
<figure class='code'><figcaption><span>start</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class='bash'><span class='line'><span class="nb">cd</span> <span class="nv">$OPENSHIFT_REPO_DIR</span>
</span><span class='line'>java -jar target/gomoku-1.0.jar server gomoku.yml
</span></code></pre></td></tr></table></div></figure>
<p>After this my Gomoku app is up and ready to serve requests.
To summarize, the whole workflow is:</p>
<pre><code>* Push your changes into your OpenShift Git repo
* Commit hooks got call, in turn it: builds, deploys and starts your app
* Serve!
</code></pre>
<p>I was new to OpenShift and got the whole done in under an hour. I bet the pre-defined cartriges (JBoss or Tomcat) can even speed up this process even more.</p>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[Java Proxy Chaining - Aspect on the Cheap]]></title>
<link href="http://dmly.github.io/blog/2013/04/28/java-proxy-chaining-aspect-on-the-cheap/"/>
<updated>2013-04-28T21:01:00+00:00</updated>
<id>http://dmly.github.io/blog/2013/04/28/java-proxy-chaining-aspect-on-the-cheap</id>
<content type="html"><![CDATA[<p>How many of you have written a caching solution for one of your expensive method calls? Or how about retry logic for your service calls?
Living in such a connected world no single application is its own island. For every applications I have worked for, there always external dependencies, either other service APIs or
databases that we need to rely upon. And we can’t make the assumption that they are reliable 100% either.</p>
<p>Some service calls are expensive and the underlying data don’t change so often. We tend to cache the results. A naive approach would be to find such methods and refactor them
so that cache can be used before the call to the services are made. The better way is to use AOP where you intercept those calls with ‘aspects’. The in those aspects you can make the decision to whether get the results from the cache or to make the expensive service calls.
Another common scenario is retry when you encounter exceptions in your service calls: transient network issues (latency, timed out, spillover in load balancer…) or database hiccups.
Normally, you should at least retry the calls for several times before giving up. Like noted previously, a naive approach would be to go every methods and apply the retry logic. Or you could use AOP.</p>
<p>In this post, I’m going to talk about how to use aspect oriented way to ease the refactoring effort. I will not talk about the full blown bytecode level AOP solution which uses AspectJ
with bytecode weaving. Instead, I will talk about a lighter weight of aspect programming using the Java’s dynamic proxy and its reflection mechanism. I think it’s pretty similar to the way Spring
AOP works. The only difference is that my code will assume every method calls implement interfaces. Thus, it will not have to use cglib to generate the proxies. Also, I think programming to interface
is a much cleaner and prefer way for your service calls Data access objects (DAO).</p>
<p>At the end you could decorate your method with annotations/aspects like this:</p>
<figure class='code'><figcaption><span>Example</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="nd">@Timeit</span>
</span><span class='line'><span class="nd">@Retry</span><span class="o">(</span><span class="n">times</span><span class="o">=</span><span class="mi">3</span><span class="o">)</span>
</span><span class='line'><span class="nd">@Cache</span><span class="o">(</span><span class="n">timeToLiveInSeconds</span><span class="o">=</span><span class="mi">3600</span><span class="o">)</span>
</span><span class='line'><span class="kd">public</span> <span class="kt">void</span> <span class="nf">goGetMyData</span><span class="o">(</span><span class="n">String</span> <span class="n">someParam</span><span class="o">,</span> <span class="kt">int</span> <span class="n">anotherOne</span><span class="o">)</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="c1">// do something</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
<!-- more -->
<p>Let’s define an example interface for the DAO and its implementation.</p>
<figure class='code'><figcaption><span>Interface</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
<span class='line-number'>9</span>
<span class='line-number'>10</span>
<span class='line-number'>11</span>
<span class='line-number'>12</span>
<span class='line-number'>13</span>
<span class='line-number'>14</span>
<span class='line-number'>15</span>
<span class='line-number'>16</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="kd">interface</span> <span class="nc">Say</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="kd">public</span> <span class="kt">void</span> <span class="nf">say</span><span class="o">();</span>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="kd">public</span> <span class="kt">void</span> <span class="nf">say</span><span class="o">()</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="n">Random</span> <span class="n">rand</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Random</span><span class="o">();</span>
</span><span class='line'> <span class="kt">int</span> <span class="n">r</span> <span class="o">=</span> <span class="n">rand</span><span class="o">.</span><span class="na">nextInt</span><span class="o">(</span><span class="mi">9</span><span class="o">);</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">r</span> <span class="o">></span> <span class="mi">7</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">throw</span> <span class="k">new</span> <span class="nf">RuntimeException</span><span class="o">(</span><span class="s">"CRAP please retry!!"</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="s">"Say hello"</span><span class="o">);</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
<p>I intentionally throw a RuntimeException 30% of the times this method run to simulation transient error that could be retried.
Now is the fun part: we will add additional functionalities over this method without modifying its code. As the begining I want to time the method performance
and retry if it fails (up to 3 times before I give up).</p>
<p>The easiest way to do this is to use annotation to denote your new aspects.</p>
<figure class='code'><figcaption><span>Timing Aspect Annotation</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="nd">@Target</span><span class="o">(</span><span class="n">ElementType</span><span class="o">.</span><span class="na">METHOD</span><span class="o">)</span>
</span><span class='line'><span class="nd">@Retention</span><span class="o">(</span><span class="n">RetentionPolicy</span><span class="o">.</span><span class="na">RUNTIME</span><span class="o">)</span>
</span><span class='line'><span class="nd">@interface</span> <span class="n">Timeit</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
<p>And the Retry aspect with maximum of 3 retries before giving up:</p>
<figure class='code'><figcaption><span>Retry Aspect</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="nd">@Target</span><span class="o">(</span><span class="n">ElementType</span><span class="o">.</span><span class="na">METHOD</span><span class="o">)</span>
</span><span class='line'><span class="nd">@Retention</span><span class="o">(</span><span class="n">RetentionPolicy</span><span class="o">.</span><span class="na">RUNTIME</span><span class="o">)</span>
</span><span class='line'><span class="nd">@interface</span> <span class="n">Retry</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="kt">int</span> <span class="nf">times</span><span class="o">()</span> <span class="k">default</span> <span class="mi">3</span><span class="o">;</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
<p>In order to facilitate the annotations in the java dynamic proxy, we need to create an InvocationHandler for each of those annotations.
For this I first borrow the utility class from “Java Reflection in Action”. You can get full source at the end of this post.
I then create a base Interceptor on top of this invocation handler to make the dynamic proxy generation handling annotations easier.</p>
<figure class='code'><figcaption><span>AbstractInvocationHandler and The base Invoker</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
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<span class='line-number'>10</span>
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<span class='line-number'>12</span>
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<span class='line-number'>14</span>
<span class='line-number'>15</span>
<span class='line-number'>16</span>
<span class='line-number'>17</span>
<span class='line-number'>18</span>
<span class='line-number'>19</span>
<span class='line-number'>20</span>
<span class='line-number'>21</span>
<span class='line-number'>22</span>
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<span class='line-number'>30</span>
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<span class='line-number'>32</span>
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<span class='line-number'>34</span>
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<span class='line-number'>36</span>
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<span class='line-number'>38</span>
<span class='line-number'>39</span>
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<span class='line-number'>41</span>
<span class='line-number'>42</span>
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<span class='line-number'>56</span>
<span class='line-number'>57</span>
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<span class='line-number'>60</span>
<span class='line-number'>61</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractInvocationHandler</span><span class="o"><</span><span class="n">T</span><span class="o">></span> <span class="kd">implements</span> <span class="n">InvocationHandler</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">protected</span> <span class="n">T</span> <span class="n">nextTarget</span><span class="o">;</span>
</span><span class='line'> <span class="kd">protected</span> <span class="n">T</span> <span class="n">realTarget</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">public</span> <span class="nf">AbstractInvocationHandler</span><span class="o">(</span><span class="n">T</span> <span class="n">target</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">nextTarget</span> <span class="o">=</span> <span class="n">target</span><span class="o">;</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">nextTarget</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">realTarget</span> <span class="o">=</span> <span class="n">findRealTarget</span><span class="o">(</span><span class="n">nextTarget</span><span class="o">);</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">realTarget</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span>
</span><span class='line'> <span class="k">throw</span> <span class="k">new</span> <span class="nf">RuntimeException</span><span class="o">(</span><span class="s">"findRealTarget failure"</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">...</span>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="kd">interface</span> <span class="nc">RealInvoker</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">invoke</span><span class="o">()</span> <span class="kd">throws</span> <span class="n">Throwable</span><span class="o">;</span>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="kd">interface</span> <span class="nc">Invoker</span><span class="o"><</span><span class="n">A</span> <span class="kd">extends</span> <span class="n">Annotation</span><span class="o">></span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">execute</span><span class="o">(</span><span class="kd">final</span> <span class="n">Method</span> <span class="n">method</span><span class="o">,</span> <span class="kd">final</span> <span class="n">Object</span><span class="o">[]</span> <span class="n">args</span><span class="o">,</span> <span class="n">A</span> <span class="n">ann</span><span class="o">,</span> <span class="n">RealInvoker</span> <span class="n">realInvoker</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Throwable</span><span class="o">;</span>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="kd">class</span> <span class="nc">Interceptor</span><span class="o"><</span><span class="n">T</span><span class="o">,</span> <span class="n">A</span> <span class="kd">extends</span> <span class="n">Annotation</span><span class="o">></span> <span class="kd">extends</span> <span class="n">AbstractInvocationHandler</span><span class="o"><</span><span class="n">T</span><span class="o">></span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="o">...</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">public</span> <span class="kd">static</span> <span class="o"><</span><span class="n">T</span><span class="o">,</span> <span class="n">A</span> <span class="kd">extends</span> <span class="n">Annotation</span><span class="o">></span> <span class="n">T</span> <span class="n">createProxy</span><span class="o">(</span><span class="n">T</span> <span class="n">obj</span><span class="o">,</span> <span class="n">Class</span><span class="o"><</span><span class="n">A</span><span class="o">></span> <span class="n">annotationClass</span><span class="o">,</span> <span class="n">Invoker</span><span class="o"><</span><span class="n">A</span><span class="o">></span> <span class="n">invoker</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="o">(</span><span class="n">T</span><span class="o">)</span> <span class="n">Proxy</span><span class="o">.</span><span class="na">newProxyInstance</span><span class="o">(</span><span class="n">obj</span><span class="o">.</span><span class="na">getClass</span><span class="o">().</span><span class="na">getClassLoader</span><span class="o">(),</span> <span class="n">obj</span>
</span><span class='line'> <span class="o">.</span><span class="na">getClass</span><span class="o">().</span><span class="na">getInterfaces</span><span class="o">(),</span> <span class="k">new</span> <span class="n">Interceptor</span><span class="o">(</span><span class="n">obj</span><span class="o">,</span> <span class="n">annotationClass</span><span class="o">,</span> <span class="n">invoker</span><span class="o">));</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="nd">@Override</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">invoke</span><span class="o">(</span><span class="n">Object</span> <span class="n">proxy</span><span class="o">,</span> <span class="kd">final</span> <span class="n">Method</span> <span class="n">method</span><span class="o">,</span> <span class="kd">final</span> <span class="n">Object</span><span class="o">[]</span> <span class="n">args</span><span class="o">)</span>
</span><span class='line'> <span class="kd">throws</span> <span class="n">Throwable</span> <span class="o">{</span>
</span><span class='line'> <span class="n">Object</span> <span class="n">result</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span><span class='line'> <span class="n">A</span> <span class="n">annotation</span> <span class="o">=</span> <span class="o">(</span><span class="n">A</span><span class="o">)</span> <span class="k">this</span><span class="o">.</span><span class="na">realTarget</span><span class="o">.</span><span class="na">getClass</span><span class="o">().</span><span class="na">getMethod</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()).</span><span class="na">getAnnotation</span><span class="o">(</span><span class="n">annotationClass</span><span class="o">);</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">annotation</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="n">invoker</span><span class="o">.</span><span class="na">execute</span><span class="o">(</span><span class="n">method</span><span class="o">,</span> <span class="n">args</span><span class="o">,</span> <span class="n">annotation</span><span class="o">,</span> <span class="k">new</span> <span class="n">RealInvoker</span><span class="o">()</span> <span class="o">{</span>
</span><span class='line'> <span class="nd">@Override</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">invoke</span><span class="o">()</span> <span class="kd">throws</span> <span class="n">Throwable</span> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">Interceptor</span><span class="o">.</span><span class="na">this</span><span class="o">.</span><span class="na">nextTarget</span><span class="o">,</span> <span class="n">args</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">});</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="k">else</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">result</span> <span class="o">=</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">nextTarget</span><span class="o">,</span> <span class="n">args</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="k">return</span> <span class="n">result</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
<p>The nice thing in doing this is that in order to create an aspect based on an annotation you just need to implement the Invoker interface shown above.
Then you can create the dynamic proxy of the targeted object by calling:</p>
<figure class='code'><figcaption><span>Creating the Dynamic Proxy</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="c1">// Some dao needed to be wrapped in Timeit aspect</span>
</span><span class='line'><span class="n">SomeDao</span> <span class="n">dao</span> <span class="o">=</span> <span class="o">...</span>
</span><span class='line'><span class="n">dao</span> <span class="o">=</span> <span class="n">Interceptor</span><span class="o">.</span><span class="na">createProxy</span><span class="o">(</span><span class="n">dao</span><span class="o">,</span> <span class="n">Timeit</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="k">new</span> <span class="n">TimerAspect</span><span class="o">());</span>
</span></code></pre></td></tr></table></div></figure>
<p>Interceptor.createProxy takes 3 arguments: the targeted object to be proxied, the aspect annotation class and the object to handle the aspect.
For the Timer (or Timeit) aspect, it could be as simple as this:</p>
<figure class='code'><figcaption><span>Timeit Aspect</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
<span class='line-number'>9</span>
<span class='line-number'>10</span>
<span class='line-number'>11</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="kd">public</span> <span class="kd">class</span> <span class="nc">TimerAspect</span> <span class="kd">implements</span> <span class="n">Invoker</span><span class="o"><</span><span class="n">Timeit</span><span class="o">></span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="nd">@Override</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">execute</span><span class="o">(</span><span class="n">Method</span> <span class="n">method</span><span class="o">,</span> <span class="n">Object</span><span class="o">[]</span> <span class="n">args</span><span class="o">,</span> <span class="n">Timeit</span> <span class="n">ann</span><span class="o">,</span>
</span><span class='line'> <span class="n">RealInvoker</span> <span class="n">realInvoker</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Throwable</span> <span class="o">{</span>
</span><span class='line'> <span class="kt">long</span> <span class="n">start</span> <span class="o">=</span> <span class="n">System</span><span class="o">.</span><span class="na">nanoTime</span><span class="o">();</span>
</span><span class='line'> <span class="n">Object</span> <span class="n">result</span> <span class="o">=</span> <span class="n">realInvoker</span><span class="o">.</span><span class="na">invoke</span><span class="o">();</span>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="n">String</span><span class="o">.</span><span class="na">format</span><span class="o">(</span><span class="s">"-- %s tookkkk %s ms"</span><span class="o">,</span> <span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">(),</span> <span class="o">(</span><span class="n">System</span><span class="o">.</span><span class="na">nanoTime</span><span class="o">()</span> <span class="o">-</span> <span class="n">start</span><span class="o">)</span> <span class="o">/</span> <span class="mf">1000000.0</span><span class="o">));</span>
</span><span class='line'> <span class="k">return</span> <span class="n">result</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
<p>Here is why this is an aspect: the execute method takes note of the current time. It then invokes the original method call. Finally it calculates
how long this method call takes. I believe in AspectJ this is called “before and around pointcut”.</p>
<p>Similarly, I would create the Retry aspect by implementing the Invoker interface and call</p>
<figure class='code'><figcaption><span>Creating Retry aspect</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="n">dao</span> <span class="o">=</span> <span class="n">Interceptor</span><span class="o">.</span><span class="na">createProxy</span><span class="o">(</span><span class="n">dao</span><span class="o">,</span> <span class="n">Retry</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="k">new</span> <span class="n">RetryAspect</span><span class="o">());</span>
</span></code></pre></td></tr></table></div></figure>
<p>After we have the aspects to handle those annotations, how do chain them in a correct order, an order which makes sense at all?
It all depends on your aspects’ logic but in this case I would make the Timer aspect outside of the Retry aspect. Confused? Here is the order of execution:</p>
<pre><code>1. Enter the Timer aspect, take note of the current time
2. Enter the Retry aspect, retry count set to 0
3. Invoke the actual Dao method
4. If it fails, retry aspect catch the exception and retries! It keeps track of the number of retries (up to 3 times by default)
5. Either the call fails if retries exceed 3 times or it exits the Retry aspect and yield the command to Timer Aspect again
6. Timer aspect calculate how long this Dao method takes
7. Return the result to the caller
</code></pre>
<p>One thing you need to pay close attention is the order of the execution of those chained aspects influenced by the way you create them.
The inner most aspect will need to be created last. The outer most aspect will need to be created first.
For this example, this is the order of aspect creation:</p>
<figure class='code'><figcaption><span>Order of Aspect creation</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="n">SomeDao</span> <span class="n">dao</span> <span class="o">=</span> <span class="o">...</span>
</span><span class='line'><span class="n">dao</span> <span class="o">=</span> <span class="n">Interceptor</span><span class="o">.</span><span class="na">createProxy</span><span class="o">(</span><span class="n">dao</span><span class="o">,</span> <span class="n">Retry</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="k">new</span> <span class="n">RetryAspect</span><span class="o">());</span>
</span><span class='line'><span class="n">dao</span> <span class="o">=</span> <span class="n">Interceptor</span><span class="o">.</span><span class="na">createProxy</span><span class="o">(</span><span class="n">dao</span><span class="o">,</span> <span class="n">Timeit</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="k">new</span> <span class="n">TimerAspect</span><span class="o">());</span>
</span></code></pre></td></tr></table></div></figure>
<p>Here is the complete code in 2 simple classes. I hope you find this useful.</p>
<figure class='code'><figcaption><span>AbstractInvocationHandler.java</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
<span class='line-number'>9</span>
<span class='line-number'>10</span>
<span class='line-number'>11</span>
<span class='line-number'>12</span>
<span class='line-number'>13</span>
<span class='line-number'>14</span>
<span class='line-number'>15</span>
<span class='line-number'>16</span>
<span class='line-number'>17</span>
<span class='line-number'>18</span>
<span class='line-number'>19</span>
<span class='line-number'>20</span>
<span class='line-number'>21</span>
<span class='line-number'>22</span>
<span class='line-number'>23</span>
<span class='line-number'>24</span>
<span class='line-number'>25</span>
<span class='line-number'>26</span>
<span class='line-number'>27</span>
<span class='line-number'>28</span>
<span class='line-number'>29</span>
<span class='line-number'>30</span>
<span class='line-number'>31</span>
<span class='line-number'>32</span>
<span class='line-number'>33</span>
<span class='line-number'>34</span>
<span class='line-number'>35</span>
<span class='line-number'>36</span>
<span class='line-number'>37</span>
<span class='line-number'>38</span>
<span class='line-number'>39</span>
<span class='line-number'>40</span>
<span class='line-number'>41</span>
<span class='line-number'>42</span>
<span class='line-number'>43</span>
<span class='line-number'>44</span>
<span class='line-number'>45</span>
<span class='line-number'>46</span>
<span class='line-number'>47</span>
<span class='line-number'>48</span>
<span class='line-number'>49</span>
<span class='line-number'>50</span>
<span class='line-number'>51</span>
<span class='line-number'>52</span>
<span class='line-number'>53</span>
<span class='line-number'>54</span>
<span class='line-number'>55</span>
<span class='line-number'>56</span>
<span class='line-number'>57</span>
<span class='line-number'>58</span>
<span class='line-number'>59</span>
<span class='line-number'>60</span>
<span class='line-number'>61</span>
<span class='line-number'>62</span>
<span class='line-number'>63</span>
<span class='line-number'>64</span>
<span class='line-number'>65</span>
<span class='line-number'>66</span>
<span class='line-number'>67</span>
<span class='line-number'>68</span>
<span class='line-number'>69</span>
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</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="kn">import</span> <span class="nn">java.lang.reflect.*</span><span class="o">;</span>
</span><span class='line'>
</span><span class='line'><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractInvocationHandler</span><span class="o"><</span><span class="n">T</span><span class="o">></span> <span class="kd">implements</span> <span class="n">InvocationHandler</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">protected</span> <span class="n">T</span> <span class="n">nextTarget</span><span class="o">;</span>
</span><span class='line'> <span class="kd">protected</span> <span class="n">T</span> <span class="n">realTarget</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">public</span> <span class="nf">AbstractInvocationHandler</span><span class="o">(</span><span class="n">T</span> <span class="n">target</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">nextTarget</span> <span class="o">=</span> <span class="n">target</span><span class="o">;</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">nextTarget</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">realTarget</span> <span class="o">=</span> <span class="n">findRealTarget</span><span class="o">(</span><span class="n">nextTarget</span><span class="o">);</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">realTarget</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span>
</span><span class='line'> <span class="k">throw</span> <span class="k">new</span> <span class="nf">RuntimeException</span><span class="o">(</span><span class="s">"findRealTarget failure"</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">protected</span> <span class="kd">final</span> <span class="n">T</span> <span class="nf">getRealTarget</span><span class="o">()</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="n">realTarget</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">protected</span> <span class="kd">static</span> <span class="kd">final</span> <span class="o"><</span><span class="n">T</span><span class="o">></span> <span class="n">T</span> <span class="n">findRealTarget</span><span class="o">(</span><span class="n">T</span> <span class="n">t</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(!</span><span class="n">Proxy</span><span class="o">.</span><span class="na">isProxyClass</span><span class="o">(</span><span class="n">t</span><span class="o">.</span><span class="na">getClass</span><span class="o">()))</span>
</span><span class='line'> <span class="k">return</span> <span class="n">t</span><span class="o">;</span>
</span><span class='line'> <span class="n">InvocationHandler</span> <span class="n">ih</span> <span class="o">=</span> <span class="n">Proxy</span><span class="o">.</span><span class="na">getInvocationHandler</span><span class="o">(</span><span class="n">t</span><span class="o">);</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">AbstractInvocationHandler</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">isInstance</span><span class="o">(</span><span class="n">ih</span><span class="o">))</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="o">(</span><span class="n">T</span><span class="o">)</span> <span class="o">((</span><span class="n">AbstractInvocationHandler</span><span class="o">)</span> <span class="n">ih</span><span class="o">).</span><span class="na">getRealTarget</span><span class="o">();</span>
</span><span class='line'> <span class="o">}</span> <span class="k">else</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">try</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">Field</span> <span class="n">f</span> <span class="o">=</span> <span class="n">findField</span><span class="o">(</span><span class="n">ih</span><span class="o">.</span><span class="na">getClass</span><span class="o">(),</span> <span class="s">"target"</span><span class="o">);</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">Object</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">isAssignableFrom</span><span class="o">(</span><span class="n">f</span><span class="o">.</span><span class="na">getType</span><span class="o">())</span>
</span><span class='line'> <span class="o">&&</span> <span class="o">!</span><span class="n">f</span><span class="o">.</span><span class="na">getType</span><span class="o">().</span><span class="na">isArray</span><span class="o">())</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'>
</span><span class='line'> <span class="n">f</span><span class="o">.</span><span class="na">setAccessible</span><span class="o">(</span><span class="kc">true</span><span class="o">);</span> <span class="c1">// suppress access checks</span>
</span><span class='line'> <span class="n">Object</span> <span class="n">innerTarget</span> <span class="o">=</span> <span class="n">f</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="n">ih</span><span class="o">);</span>
</span><span class='line'> <span class="k">return</span> <span class="o">(</span><span class="n">T</span><span class="o">)</span> <span class="n">findRealTarget</span><span class="o">(</span><span class="n">innerTarget</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">NoSuchFieldException</span> <span class="n">e</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">SecurityException</span> <span class="n">e</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">IllegalAccessException</span> <span class="n">e</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span> <span class="c1">// IllegalArgumentException cannot be raised</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">public</span> <span class="kd">static</span> <span class="n">Field</span> <span class="nf">findField</span><span class="o">(</span><span class="n">Class</span> <span class="n">cls</span><span class="o">,</span> <span class="n">String</span> <span class="n">name</span><span class="o">)</span>
</span><span class='line'> <span class="kd">throws</span> <span class="n">NoSuchFieldException</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">cls</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">try</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="n">cls</span><span class="o">.</span><span class="na">getDeclaredField</span><span class="o">(</span><span class="n">name</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">NoSuchFieldException</span> <span class="n">e</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="nf">findField</span><span class="o">(</span><span class="n">cls</span><span class="o">.</span><span class="na">getSuperclass</span><span class="o">(),</span> <span class="n">name</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">}</span> <span class="k">else</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">throw</span> <span class="k">new</span> <span class="nf">NoSuchFieldException</span><span class="o">();</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
<figure class='code'><figcaption><span>Main.java</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
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</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="kn">import</span> <span class="nn">java.lang.annotation.Annotation</span><span class="o">;</span>
</span><span class='line'><span class="kn">import</span> <span class="nn">java.lang.annotation.ElementType</span><span class="o">;</span>
</span><span class='line'><span class="kn">import</span> <span class="nn">java.lang.annotation.Retention</span><span class="o">;</span>
</span><span class='line'><span class="kn">import</span> <span class="nn">java.lang.annotation.RetentionPolicy</span><span class="o">;</span>
</span><span class='line'><span class="kn">import</span> <span class="nn">java.lang.annotation.Target</span><span class="o">;</span>
</span><span class='line'><span class="kn">import</span> <span class="nn">java.lang.reflect.InvocationHandler</span><span class="o">;</span>
</span><span class='line'><span class="kn">import</span> <span class="nn">java.lang.reflect.Method</span><span class="o">;</span>
</span><span class='line'><span class="kn">import</span> <span class="nn">java.lang.reflect.Proxy</span><span class="o">;</span>
</span><span class='line'><span class="kn">import</span> <span class="nn">java.util.Random</span><span class="o">;</span>
</span><span class='line'>
</span><span class='line'><span class="kd">interface</span> <span class="nc">RealInvoker</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">invoke</span><span class="o">()</span> <span class="kd">throws</span> <span class="n">Throwable</span><span class="o">;</span>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="kd">interface</span> <span class="nc">Invoker</span><span class="o"><</span><span class="n">A</span> <span class="kd">extends</span> <span class="n">Annotation</span><span class="o">></span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">execute</span><span class="o">(</span><span class="kd">final</span> <span class="n">Method</span> <span class="n">method</span><span class="o">,</span> <span class="kd">final</span> <span class="n">Object</span><span class="o">[]</span> <span class="n">args</span><span class="o">,</span> <span class="n">A</span> <span class="n">ann</span><span class="o">,</span> <span class="n">RealInvoker</span> <span class="n">realInvoker</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Throwable</span><span class="o">;</span>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="kd">class</span> <span class="nc">Interceptor</span><span class="o"><</span><span class="n">T</span><span class="o">,</span> <span class="n">A</span> <span class="kd">extends</span> <span class="n">Annotation</span><span class="o">></span> <span class="kd">extends</span> <span class="n">AbstractInvocationHandler</span><span class="o"><</span><span class="n">T</span><span class="o">></span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="kd">private</span> <span class="n">Class</span><span class="o"><</span><span class="n">A</span><span class="o">></span> <span class="n">annotationClass</span><span class="o">;</span>
</span><span class='line'> <span class="kd">private</span> <span class="n">Invoker</span><span class="o"><</span><span class="n">A</span><span class="o">></span> <span class="n">invoker</span><span class="o">;</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">private</span> <span class="nf">Interceptor</span><span class="o">(</span><span class="n">T</span> <span class="n">target</span><span class="o">,</span> <span class="n">Class</span><span class="o"><</span><span class="n">A</span><span class="o">></span> <span class="n">annotationClass</span><span class="o">,</span> <span class="n">Invoker</span><span class="o"><</span><span class="n">A</span><span class="o">></span> <span class="n">invoker</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="kd">super</span><span class="o">(</span><span class="n">target</span><span class="o">);</span>
</span><span class='line'> <span class="k">this</span><span class="o">.</span><span class="na">annotationClass</span> <span class="o">=</span> <span class="n">annotationClass</span><span class="o">;</span>
</span><span class='line'> <span class="k">this</span><span class="o">.</span><span class="na">invoker</span> <span class="o">=</span> <span class="n">invoker</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">public</span> <span class="kd">static</span> <span class="o"><</span><span class="n">T</span><span class="o">,</span> <span class="n">A</span> <span class="kd">extends</span> <span class="n">Annotation</span><span class="o">></span> <span class="n">T</span> <span class="n">createProxy</span><span class="o">(</span><span class="n">T</span> <span class="n">obj</span><span class="o">,</span> <span class="n">Class</span><span class="o"><</span><span class="n">A</span><span class="o">></span> <span class="n">annotationClass</span><span class="o">,</span> <span class="n">Invoker</span><span class="o"><</span><span class="n">A</span><span class="o">></span> <span class="n">invoker</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="o">(</span><span class="n">T</span><span class="o">)</span> <span class="n">Proxy</span><span class="o">.</span><span class="na">newProxyInstance</span><span class="o">(</span><span class="n">obj</span><span class="o">.</span><span class="na">getClass</span><span class="o">().</span><span class="na">getClassLoader</span><span class="o">(),</span> <span class="n">obj</span>
</span><span class='line'> <span class="o">.</span><span class="na">getClass</span><span class="o">().</span><span class="na">getInterfaces</span><span class="o">(),</span> <span class="k">new</span> <span class="n">Interceptor</span><span class="o">(</span><span class="n">obj</span><span class="o">,</span> <span class="n">annotationClass</span><span class="o">,</span> <span class="n">invoker</span><span class="o">));</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="nd">@Override</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">invoke</span><span class="o">(</span><span class="n">Object</span> <span class="n">proxy</span><span class="o">,</span> <span class="kd">final</span> <span class="n">Method</span> <span class="n">method</span><span class="o">,</span> <span class="kd">final</span> <span class="n">Object</span><span class="o">[]</span> <span class="n">args</span><span class="o">)</span>
</span><span class='line'> <span class="kd">throws</span> <span class="n">Throwable</span> <span class="o">{</span>
</span><span class='line'> <span class="n">Object</span> <span class="n">result</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span><span class='line'> <span class="n">A</span> <span class="n">annotation</span> <span class="o">=</span> <span class="o">(</span><span class="n">A</span><span class="o">)</span> <span class="k">this</span><span class="o">.</span><span class="na">realTarget</span><span class="o">.</span><span class="na">getClass</span><span class="o">().</span><span class="na">getMethod</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()).</span><span class="na">getAnnotation</span><span class="o">(</span><span class="n">annotationClass</span><span class="o">);</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">annotation</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="n">invoker</span><span class="o">.</span><span class="na">execute</span><span class="o">(</span><span class="n">method</span><span class="o">,</span> <span class="n">args</span><span class="o">,</span> <span class="n">annotation</span><span class="o">,</span> <span class="k">new</span> <span class="n">RealInvoker</span><span class="o">()</span> <span class="o">{</span>
</span><span class='line'> <span class="nd">@Override</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">invoke</span><span class="o">()</span> <span class="kd">throws</span> <span class="n">Throwable</span> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">Interceptor</span><span class="o">.</span><span class="na">this</span><span class="o">.</span><span class="na">nextTarget</span><span class="o">,</span> <span class="n">args</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">});</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="k">else</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">result</span> <span class="o">=</span> <span class="n">method</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">nextTarget</span><span class="o">,</span> <span class="n">args</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="k">return</span> <span class="n">result</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="nd">@Target</span><span class="o">(</span><span class="n">ElementType</span><span class="o">.</span><span class="na">METHOD</span><span class="o">)</span>
</span><span class='line'><span class="nd">@Retention</span><span class="o">(</span><span class="n">RetentionPolicy</span><span class="o">.</span><span class="na">RUNTIME</span><span class="o">)</span>
</span><span class='line'><span class="nd">@interface</span> <span class="n">Timeit</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="nd">@Target</span><span class="o">(</span><span class="n">ElementType</span><span class="o">.</span><span class="na">METHOD</span><span class="o">)</span>
</span><span class='line'><span class="nd">@Retention</span><span class="o">(</span><span class="n">RetentionPolicy</span><span class="o">.</span><span class="na">RUNTIME</span><span class="o">)</span>
</span><span class='line'><span class="nd">@interface</span> <span class="n">Cache</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="nd">@Target</span><span class="o">(</span><span class="n">ElementType</span><span class="o">.</span><span class="na">METHOD</span><span class="o">)</span>
</span><span class='line'><span class="nd">@Retention</span><span class="o">(</span><span class="n">RetentionPolicy</span><span class="o">.</span><span class="na">RUNTIME</span><span class="o">)</span>
</span><span class='line'><span class="nd">@interface</span> <span class="n">Retry</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="kt">int</span> <span class="nf">times</span><span class="o">()</span> <span class="k">default</span> <span class="mi">3</span><span class="o">;</span>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="kd">interface</span> <span class="nc">Say</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="kd">public</span> <span class="kt">void</span> <span class="nf">say</span><span class="o">();</span>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="kd">class</span> <span class="nc">ProxyFactory</span><span class="o"><</span><span class="n">T</span><span class="o">></span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="kd">public</span> <span class="kd">static</span> <span class="o"><</span><span class="n">T</span><span class="o">></span> <span class="n">T</span> <span class="n">createProxy</span><span class="o">(</span><span class="n">T</span> <span class="n">obj</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">obj</span> <span class="o">=</span> <span class="n">Interceptor</span><span class="o">.</span><span class="na">createProxy</span><span class="o">(</span><span class="n">obj</span><span class="o">,</span> <span class="n">Retry</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="k">new</span> <span class="n">Invoker</span><span class="o"><</span><span class="n">Retry</span><span class="o">>()</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="nd">@Override</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">execute</span><span class="o">(</span><span class="n">Method</span> <span class="n">method</span><span class="o">,</span> <span class="n">Object</span><span class="o">[]</span> <span class="n">args</span><span class="o">,</span> <span class="n">Retry</span> <span class="n">ann</span><span class="o">,</span>
</span><span class='line'> <span class="n">RealInvoker</span> <span class="n">realInvoker</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Throwable</span> <span class="o">{</span>
</span><span class='line'> <span class="n">Object</span> <span class="n">result</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span><span class='line'>
</span><span class='line'> <span class="kt">int</span> <span class="n">retries</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
</span><span class='line'> <span class="k">while</span> <span class="o">(</span><span class="n">retries</span> <span class="o"><</span> <span class="n">ann</span><span class="o">.</span><span class="na">times</span><span class="o">())</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">try</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">result</span> <span class="o">=</span> <span class="n">realInvoker</span><span class="o">.</span><span class="na">invoke</span><span class="o">();</span>
</span><span class='line'> <span class="k">break</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">crap</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">retries</span><span class="o">++;</span>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="n">String</span><span class="o">.</span><span class="na">format</span><span class="o">(</span><span class="s">"Crap catched %s times"</span><span class="o">,</span> <span class="n">retries</span><span class="o">));</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">retries</span> <span class="o">>=</span> <span class="n">ann</span><span class="o">.</span><span class="na">times</span><span class="o">())</span> <span class="k">throw</span> <span class="k">new</span> <span class="n">RuntimeException</span><span class="o">(</span><span class="s">"Can't handle it anymore"</span><span class="o">);</span>
</span><span class='line'>
</span><span class='line'> <span class="k">return</span> <span class="n">result</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">});</span>
</span><span class='line'>
</span><span class='line'> <span class="n">obj</span> <span class="o">=</span> <span class="n">Interceptor</span><span class="o">.</span><span class="na">createProxy</span><span class="o">(</span><span class="n">obj</span><span class="o">,</span> <span class="n">Timeit</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="k">new</span> <span class="n">Invoker</span><span class="o"><</span><span class="n">Timeit</span><span class="o">>()</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="nd">@Override</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">execute</span><span class="o">(</span><span class="n">Method</span> <span class="n">method</span><span class="o">,</span> <span class="n">Object</span><span class="o">[]</span> <span class="n">args</span><span class="o">,</span> <span class="n">Timeit</span> <span class="n">ann</span><span class="o">,</span>
</span><span class='line'> <span class="n">RealInvoker</span> <span class="n">realInvoker</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Throwable</span> <span class="o">{</span>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="s">"-- Enter the timer"</span><span class="o">);</span>
</span><span class='line'> <span class="kt">long</span> <span class="n">start</span> <span class="o">=</span> <span class="n">System</span><span class="o">.</span><span class="na">nanoTime</span><span class="o">();</span>
</span><span class='line'> <span class="n">Object</span> <span class="n">result</span> <span class="o">=</span> <span class="n">realInvoker</span><span class="o">.</span><span class="na">invoke</span><span class="o">();</span>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="n">String</span><span class="o">.</span><span class="na">format</span><span class="o">(</span><span class="s">"-- %s tookkkk %s ms"</span><span class="o">,</span> <span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">(),</span> <span class="o">(</span><span class="n">System</span><span class="o">.</span><span class="na">nanoTime</span><span class="o">()</span> <span class="o">-</span> <span class="n">start</span><span class="o">)</span> <span class="o">/</span> <span class="mf">1000000.0</span><span class="o">));</span>
</span><span class='line'> <span class="k">return</span> <span class="n">result</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">});</span>
</span><span class='line'>
</span><span class='line'> <span class="k">return</span> <span class="n">obj</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'><span class="o">}</span>
</span><span class='line'>
</span><span class='line'><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Main</span> <span class="kd">implements</span> <span class="n">Say</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="kd">public</span> <span class="kd">static</span> <span class="kt">void</span> <span class="nf">main</span><span class="o">(</span><span class="n">String</span><span class="o">...</span> <span class="n">args</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">Say</span> <span class="n">main</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Main</span><span class="o">();</span>
</span><span class='line'> <span class="n">main</span> <span class="o">=</span> <span class="n">ProxyFactory</span><span class="o">.</span><span class="na">createProxy</span><span class="o">(</span><span class="n">main</span><span class="o">);</span>
</span><span class='line'>
</span><span class='line'> <span class="k">for</span> <span class="o">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span> <span class="n">i</span> <span class="o"><</span> <span class="mi">10</span><span class="o">;</span> <span class="n">i</span><span class="o">++)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">main</span><span class="o">.</span><span class="na">say</span><span class="o">();</span>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="s">" ##### \n"</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="nd">@Timeit</span>
</span><span class='line'> <span class="nd">@Retry</span>
</span><span class='line'> <span class="kd">public</span> <span class="kt">void</span> <span class="nf">say</span><span class="o">()</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">Random</span> <span class="n">rand</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Random</span><span class="o">();</span>
</span><span class='line'> <span class="kt">int</span> <span class="n">r</span> <span class="o">=</span> <span class="n">rand</span><span class="o">.</span><span class="na">nextInt</span><span class="o">(</span><span class="mi">9</span><span class="o">);</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">r</span> <span class="o">></span> <span class="mi">5</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="k">throw</span> <span class="k">new</span> <span class="nf">RuntimeException</span><span class="o">(</span><span class="s">"CRAP rety!!"</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="s">"Say hello"</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
<figure class='code'><figcaption><span>Cache Aspect</span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
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<span class='line-number'>37</span>
<span class='line-number'>38</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="kd">public</span> <span class="n">CacheAspect</span> <span class="kd">implements</span> <span class="n">Invoker</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="n">ConcurrentMap</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">ConcurrentMap</span><span class="o"><</span><span class="n">Object</span><span class="o">,</span> <span class="n">Object</span><span class="o">>></span> <span class="n">cache</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ConcurrentHashMap</span><span class="o"><>();</span>
</span><span class='line'>
</span><span class='line'> <span class="nd">@Override</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">Object</span> <span class="nf">execute</span><span class="o">(</span><span class="n">Method</span> <span class="n">method</span><span class="o">,</span> <span class="n">Object</span><span class="o">[]</span> <span class="n">args</span><span class="o">,</span> <span class="n">Cache</span> <span class="n">ann</span><span class="o">,</span>
</span><span class='line'> <span class="n">RealInvoker</span> <span class="n">realInvoker</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Throwable</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="s">"@@ Entering cache proxy with "</span> <span class="o">+</span> <span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()</span> <span class="o">+</span> <span class="s">" "</span> <span class="o">+</span> <span class="n">args</span><span class="o">);</span>
</span><span class='line'> <span class="n">ConcurrentMap</span><span class="o"><</span><span class="n">Object</span><span class="o">,</span> <span class="n">Object</span><span class="o">></span> <span class="n">theCache</span> <span class="o">=</span> <span class="n">cache</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">());</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">theCache</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">theCache</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ConcurrentHashMap</span><span class="o"><>();</span>
</span><span class='line'> <span class="n">cache</span><span class="o">.</span><span class="na">put</span><span class="o">(</span><span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">(),</span> <span class="n">theCache</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="n">Object</span> <span class="n">key</span> <span class="o">=</span> <span class="n">args</span><span class="o">;</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">args</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">key</span> <span class="o">=</span> <span class="s">""</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="n">Object</span> <span class="n">result</span> <span class="o">=</span> <span class="n">theCache</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="n">key</span><span class="o">);</span>
</span><span class='line'> <span class="k">if</span> <span class="o">(</span><span class="n">result</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="s">"@@ Cache hit with "</span> <span class="o">+</span> <span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()</span> <span class="o">+</span> <span class="s">" "</span> <span class="o">+</span> <span class="n">args</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="k">else</span>
</span><span class='line'> <span class="o">{</span>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="s">"@@ Cache missed with "</span> <span class="o">+</span> <span class="n">method</span><span class="o">.</span><span class="na">getName</span><span class="o">()</span> <span class="o">+</span> <span class="s">" "</span> <span class="o">+</span> <span class="n">args</span><span class="o">);</span>
</span><span class='line'> <span class="n">result</span> <span class="o">=</span> <span class="n">realInvoker</span><span class="o">.</span><span class="na">invoke</span><span class="o">();</span>
</span><span class='line'> <span class="n">theCache</span><span class="o">.</span><span class="na">put</span><span class="o">(</span><span class="n">key</span><span class="o">,</span> <span class="n">result</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">?</span> <span class="s">""</span> <span class="o">:</span> <span class="n">result</span><span class="o">);</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="s">"@@ Exiting cache proxy"</span><span class="o">);</span>
</span><span class='line'>
</span><span class='line'> <span class="k">return</span> <span class="n">result</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[Building Database Full Text Index with Lucene]]></title>
<link href="http://dmly.github.io/blog/2010/09/14/building-database-full-text-index-with-lucene/"/>
<updated>2010-09-14T14:15:00+00:00</updated>
<id>http://dmly.github.io/blog/2010/09/14/building-database-full-text-index-with-lucene</id>
<content type="html"><![CDATA[<p>I have this client table in Oracle having more than 3 million rows. One of the column is the client name in which our users want to have full text search support.
Originally, Oracle context search feature was choosen by a group of consultants. May be we were maintaining the domain index correctly but its performance sucks.</p>
<!-- more -->
<p>I spend most of my time troubleshooting this issue and found out that we need to run “optimize” to make the index perform well. But anyway I am tired of having to hear users’ complaints
everyday so I got rid of Oracle full text search and refactor the search service to use Apache Lucene.</p>
<p>Here is how is done:</p>
<ol>