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Let's get started with Gradle and Bck2Brwsr VM!!

The way to create new projects in Gradle is to initialize an empty skeleton. Execute (with Gradle 7.0 and JDK8 or JDK11):

$ mkdir demo
$ cd demo
demo$ gradle init --type java-application
demo$ find *
app/build.gradle
app/src/main/java/mytest/App.java
app/src/test/java/mytest/AppTest.java
gradle/wrapper/gradle-wrapper.properties
gradle/wrapper/gradle-wrapper.jar
gradlew
gradlew.bat
settings.gradle

That command gives you the skeletal structure of your project, together with ./gradlew launcher. Use it to run the sample App in the regular way:

demo$ ./gradlew run
...
:run
Hello world.

BUILD SUCCESSFUL

Now let's run it in a browser! Apply following change to your project build.gradle configuration file:

diff --git a/app/build.gradle b/app/build.gradle
index 2259ee7..adf3461 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -6,11 +6,22 @@
  * User Manual available at https://docs.gradle.org/7.0/userguide/building_java_projects.html
  */
 
+buildscript {
+    repositories {
+        mavenCentral()
+    }
+    dependencies {
+        classpath "org.apidesign.bck2brwsr:bck2brwsr-maven-plugin:0.51"
+    }
+}
+
 plugins {
     // Apply the application plugin to add support for building a CLI application in Java.
     id 'application'
 }
 
+apply plugin: 'bck2brwsr'
+
 repositories {
     // Use Maven Central for resolving dependencies.
     mavenCentral()
@@ -20,8 +31,8 @@ dependencies {
     // Use JUnit test framework.
     testImplementation 'junit:junit:4.13.1'
 
-    // This dependency is used by the application.
-    implementation 'com.google.guava:guava:30.0-jre'
+    // No need for such a huge dependency in browser
+    // implementation 'com.google.guava:guava:30.0-jre'
 }
 
 application {
jarda@xps:~/tmp/x$ git diff
diff --git a/app/build.gradle b/app/build.gradle
index 2259ee7..adf3461 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -6,11 +6,22 @@
  * User Manual available at https://docs.gradle.org/7.0/userguide/building_java_projects.html
  */
 
+buildscript {
+    repositories {
+        mavenCentral()
+    }
+    dependencies {
+        classpath "org.apidesign.bck2brwsr:bck2brwsr-maven-plugin:0.50"
+    }
+}
+
 plugins {
     // Apply the application plugin to add support for building a CLI application in Java.
     id 'application'
 }
 
+apply plugin: 'bck2brwsr'
+
 repositories {
     // Use Maven Central for resolving dependencies.
     mavenCentral()
@@ -20,8 +31,8 @@ dependencies {
     // Use JUnit test framework.
     testImplementation 'junit:junit:4.13.1'
 
-    // This dependency is used by the application.
-    implementation 'com.google.guava:guava:30.0-jre'
+    // No need for such a huge dependency in browser
+    // implementation 'com.google.guava:guava:30.0-jre'
 }
 
 application {

Now verify your build.gradle project changes are correct and your project can still be executed from a command line. Run:

demo$ ./gradlew run

> Task :app:run
Hello World!

BUILD SUCCESSFUL in 1s
2 actionable tasks: 2 executed

again. If it succeeds, your project should also be ready to be executed in a browser:

demo$ $ ./gradlew bck2brwsrShow
Starting a Gradle Daemon, 2 incompatible Daemons could not be reused, use --status for details
[INFO] Started listener bound to [0.0.0.0:28099]
[INFO] [HttpServer] Started.
[INFO] Showing http://localhost:28099/index.html
[INFO] Trying Desktop.browse on OpenJDK 64-Bit Server VM 11.0.8+10-LTS by Azul Systems, Inc.
[INFO] Desktop.browse not supported: The BROWSE action is not supported on the current platform!
[INFO] Launching [xdg-open, http://localhost:28099/index.html]

> Task :app:bck2brwsrShow
Avaiting HTTP server...
Started listener bound to [0.0.0.0:28099]
[HttpServer] Started.
Showing http://localhost:28099/index.html
Launching [xdg-open, http://localhost:28099/index.html]
Hello World!

A browser is opened and a Hello World. message gets printed into its console and also console of your terminal window.

Interacting with Java

While in browser console (press F12 to open it), you can interact with the Java virtual machine by loading public Java class and invoking its public static methods:

vm.loadClass("java.lang.System", function(System) {
  System.exit(0)
});

Coding

Your Java code is in src/main/java/App.java open it in your editor, change it and run again

demo$ ./gradlew bck2brwsrShow

Well done!

The next step is to interact with JavaScript. For that purpose Bck2Brwsr VM uses Apache HTML/Java @JavaScriptBody annotation. See the package tutorial for list of examples.

There are some ready to use libraries built around this annotation: Charts, canvas, maps. Include their coordinates in the dependency in your pom.xml and you are ready to use them all!