Result Types

Most use cases can be divided into two phases. First, we need to change or query the application’s state, and then we need to present an updated view of the application. The Action class manages the application’s state, and the Result Type manages the view.

• Predefined Result Types
• How to use results
• Default result type
• Default result name
• Default parameters
• Registering result types
• Extending

Predefined Result Types

The framework provides several implementations of the com.opensymphony.xwork2.Result interface, ready to use in your own applications.

Additional Result Types can be created and plugged into an application by implementing the com.opensymphony.xwork2.Result interface. Custom Result Types might include generating an email or JMS message, generating images, and so forth.

How to use results

Once your action has been executed it must either return a result name (as java.lang.String) or instance of com.opensymphony.xwork2.Result and then the result will be executed directly.

If a String has been returned, the framework will try to find a matching result in the configuration and then it will execute the result of a given type, see example:

<result name="success" type="dispatcher">/WEB-INF/index.jsp</result>

You can define many results per action distinguishing them by different names:

<result name="success" type="dispatcher">/WEB-INF/index.jsp</result>
<result name="input" type="dispatcher">/WEB-INF/form.jsp</result>
<result name="error" type="dispatcher">/WEB-INF/error.jsp</result>

Default result type

In struts-default.xml the Dispatcher result type is registered as a default result type, which means you don’t have to specify the type attribute if you want to use it:

<result name="success">/WEB-INF/index.jsp</result>

Default result name

If you action method returns success, which is a default name of the result, you don’t have specify the name attribute as well:

<result>/WEB-INF/index.jsp</result>

Default parameters

To minimize configuration, Results can be configured with a single value, which will be converted into a parameter, and each Result can specify which parameter this value should be set as. For example, here is a result defined in XML that uses a default parameter:

<result type="freemarker">foo.fm</result>

That is the equivalent to this:

<result type="freemarker">
  <param name="location">foo.vm</param>
</result>

Since probably 95% of your actions won’t need results that contain multiple parameters, this little shortcut saves you a significant amount of configuration. It also follows that if you have specified the default parameter, you don’t need to set the same parameter as a specifically-named parameter.

Registering result types

All Result Types are plugged in via the Result Configuration.

Extending

You can always extend defined result types and implement whatever logic you need. To simplify process of that, you can define your custom ResultFactory and use it with connection with custom interface which your Result implements. Check Define dedicated factory to see how to do it.

Struts 2 provides one such extension for you:

ParamNameAwareResult interface when used with StrutsResultBuilder can limit parameters assigned to the result. So you can simply extend existing result with such a functionality as below:

public class MyResult extends ServletDispatcherResult implements ParamNameAwareResult {

    public boolean acceptableParamName(String name, String value) {
        return "accept".equals(name);
    }

}

and then register it and use instead of default dispatcher result.