Writing a plugin for Freenet 0.7 is not that complicated.
The Code
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The Packaging
Plugins are normal JAR files that can be found everywhere in Java-speaking world. But in order for the Freenet Node to be able to load your plugin correctly you have to take care of a couple of things:
Your plugin should not use any external dependencies. Alternatively, you have to bundle the external dependency right into your JAR file. Please make sure that the license of the external dependency allows repackaging.
The JAR manifest has to include a “Plugin-Main-Class” attribute which, analog to the common “Main-Class” attribute, tells the node which class is the main class of your plugin.
Getting People to Use It
Okay, your plugin is ready, you have tested it and it works. Now you want other people to be able to use it, right? Right.
Enter the URL you gave them into the textfield in the box labelled “Add Unofficial Plugin” and click the Load button.
Now your plugin will be downloaded and stored locally to reduce load on your server. Then the manifest is searched for the “Plugin-Main-Class” attribute and the given class will be loaded. If everything worked out, your plugin will now be listed in the “Running Plugins” section of the Plugins page and will in fact be running in the background.