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Googler edited this page May 5, 2023 · 6 revisions

Struts 2 Integration

Important: The struts2 plugin is only supported up until Guice 6.0. It is not included in Guice 7.0+, because struts2 does not support the jakarta namespaces.

To install the Guice Struts 2 plugin with Struts 2.2 or later, simply include guice-struts2-plugin-<version>.jar in your web application's classpath, create a subclass of GuiceServletContextListener that implements getInjector and adds any servlets and filters (using ServletModule) and the Struts2GuicePluginModule, and a web.xml file that references your GuiceServletContextListener subclass as a listener. For examples, look at the example web.xml and GuiceServletContextListener subclass.

Guice will inject all of your Struts 2 objects including actions and interceptors. You can even scope your actions.

A Counting Example

Say for example that we want to count the number of requests in a session. Define a Counter object which will live on the session:

@SessionScoped
public class Counter {

  int count = 0;

  /** Increments the count and returns the new value. */
  public synchronized int increment() {
    return count++;
  }
}

Next, we can inject our counter into an action:

public class Count {

  final Counter counter;

  @Inject
  public Count(Counter counter) {
    this.counter = counter;
  }

  public String execute() {
    return SUCCESS;
  }

  public int getCount() {
    return counter.increment();
  }
}

Then create a mapping for our action in our struts.xml file:

<action name="Count"
    class="mypackage.Count">
  <result>/WEB-INF/Counter.jsp</result>
</action>

And a JSP to render the result:

<%@ taglib prefix="s" uri="/struts-tags" %>

<html>
  <body>
    <h1>Counter Example</h1>
    <h3><b>Hits in this session:</b>
      <s:property value="count"/></h3>
  </body>
</html>

We actually made this example more complicated than necessary in an attempt to illustrate more concepts. In reality, we could have done away with the separate Counter object and applied @SessionScoped to our action directly.

Struts2 support in earlier versions of Guice

In Guice 1.0, the struts2 extension supports struts 2.0.6 or later, and is included using the guice-struts2-plugin-1.0.jar. The struts2 extension included in Guice 2.0 did not work properly.

You must select Guice as your ObjectFactory implementation in your struts.xml file:

<constant name="struts.objectFactory" value="guice" />

You can optionally specify a Module for Guice to install in your struts.xml file:

<constant name="guice.module" value="mypackage.MyModule"/>

If all of your bindings are implicit, you can get away without defining a module at all.

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