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Struts 2 plugins
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A Struts 2 plugin is a single JAR that class and/or contain classes and configuration that extend, replace, or add to existing Struts framework functionality. A plugin can be installed by adding a its JAR file to the application's class path, in addition to the JAR files to fulfill whatever dependencies the plugin itself may have. To configure the plugin, the JAR may should contain a
struts-plugin.xml file, which follows the same format as an ordinary struts.xml file.
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Packages defined in a plugin can have parent packages that are defined in another plugin. Plugins may define configuration elements with classes not contained in the plugin. Any classes not included in the plugin's JAR must be on the application's classpath at runtime. As from Struts 2.3.5
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struts-default.xml(bundled in the Core JAR)struts-plugin.xml(as many as can be found in other JARs)struts.xml(provided by the your application)
Since the struts.xml file is always loaded last, it can make use of any resources provided by the plugins bundled with the distribution, or any other plugins available to an application.
Static resources
To include static resources in your plugins add them under "/static" in your jar. And include them in your page using "/struts" as the path, like in the following example:
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Read also StaticContentLoader JavaDoc.
Extension Points
Extension points allow a plugin to override a key class in the Struts framework with an alternate implementionimplementation. For example, a plugin could provide a new class to create Action classes or map requests to Actions.
The following extension points are available in Struts 2:
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Plugin Examples
Let's look at two similar but different plugins bundled with the core distribution.
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The sitemesh-plugin.jar contains several classes, a standard JAR manifest, and a plugin configuration file.
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While the SiteMesh Plugin doesn't provide any new results, interceptors, or actions, or even extend any Struts integration points, it does need to know what settings have been enabled in the Struts framework. Therefore, its struts-plugin.xml looks like this:
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The two bean elements, with the "static" flag enabled, tell Struts to inject the current settings and framework objects into static property setters on startup. This allows, for example, the FreeMarkerPageFilter class to get an instance of the Struts FreemarkerManager and the current encoding setting.
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The tiles-plugin.jar contains several classes, a standard JAR manifest, and a configuration file.
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Since the Tiles Plugin does need to register configuration elements, a result class, it provides a struts-plugin.xml file.
Plugin Registry
For a list of bundled plugins, see the Plugin Reference Documentation. For more about bundled and third-party plugins, visit the Apache Struts Plugin Registry.
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