SFMF4J

SFMF4J is a simple file monitoring facade for Java. It attempts to do for file monitoring what SLF4J does for logging, which is to abstract away the API from the interface, such that library developers can write code against a file monitoring solution without forcing an application developer to choose a particular file monitoring implementation.

Developing Libraries

To add file monitoring support to your library, simply declare a dependency on sfmf4j-api. In Maven:

<dependency>
    <groupId>sfmf4j</groupId>
    <artifactId>sfmf4j-api</artifactId>
    <version>${sfmf4j.version}</version>
</dependency>

Then you need to write a class that implements DirectoryListener, in order to take a particular action when a folder's contents have changed. For convenience, you may extend DirectoryListenerAdapter and override its no-op methods instead.

Developing Applications

In addition to sfmf4j-api, an application will also require a dependency on one of the SFMF4J implementations in order to support file monitoring. SFMF4J offers several out-of-the-box implementations:

• Commons IO, which uses a dedicated file system polling thread on a fixed interval.
• NIO2, the new file system API introduced in Java 7 (requires Java 7 or later).
• jpathwatch, essentially a backport of NIO2 to earlier versions of Java (uses native operating system features with a fallback to simple polling).

SPI

All of SFMF4J's provided implementations support the java.util.ServiceLoader mechanism. This means that applications can obtain FileMonitorServiceFactory instances without dodgy classpath hacks. The following code snippet demonstrates how to obtain a reference to a FileMonitorServiceFactory using the SPI approach:

public static FileMonitorServiceFactory loadFromSpi() {
    FileMonitorServiceFactory factory = null;
    ServiceLoader<FileMonitorServiceFactory> serviceLoader = ServiceLoader.load(FileMonitorServiceFactory.class);
    Iterator<FileMonitorServiceFactory> implementations = serviceLoader.iterator();
    if (iterator.hasNext()) {
        factory = iterator.next();
    }
    return factory;
}

OSGi

SFMF4J is designed to be OSGi-friendly. The sfmf4j-api module exports the package sfmf4j.api, which is imported by the implementation modules (your own bundle must also import this package). The provided implementations expose default instances of the sfmf4j.api.FileMonitorServiceFactory interface using Blueprint.