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Chaining actions in Struts

By: Apache Foundation in Struts Tutorials on 2008年09月20日 [フレーム]

Chaining actions can be done by simply using the proper mapping in your forward entries in the struts-config.xml file. Assume you had the following two classes:


 /* com/AAction.java */
 ...
 public class AAction extends Action
 {
 public ActionForward
 execute(ActionMapping mapping,
 ActionForm form,
 HttpServletRequest request,
 HttpServletResponse response) throws
 Exception
 {
 // Do something
 return mapping.findForward("success");
 }
 }


 /* com/BAction.java */
 ...
 public class BAction extends Action
 {
 public ActionForward
 execute(ActionMapping mapping,
 ActionForm form,
 HttpServletRequest request,
 HttpServletResponse response) throws
 Exception
 {
 // Do something else
 return mapping.findForward("success");
 }
 }

Then you can chain together these two actions with the Struts configuration as shown in the following excerpt:


 ...
 <action-mappings type="org.apache.struts.action.ActionMapping">
 <action path="/A"
 type="com.AAction"
 validate="false">
 <forward name="success" path="/B.do" />
 </action>
 <action path="/B"
 type="com.BAction"
 scope="session"
 validate="false">
 <forward name="success" path="/result.jsp" />
 </action>
 </action-mappings>
 ...

Here we are assuming you are using a suffix-based (.do) servlet mapping, which is recommended since module support requires it. When you send your browser to the web application and name the action A.do (i.e. http://localhost:8080/app/A.do) it will execute AAction.execute(), which will then forward to the "success" mapping.

This causes the execution of BAction.execute() since the <forward> entry for "success" in the configuration file uses the .do suffix.

Of course it is also possible to chain actions programmatically, but the power and ease of being able to "reroute" your web application's structure using the XML configuration file is much easier to maintain.

As a rule, chaining Actions is not recommended. If your business classes are properly factored, you should be able to call whatever methods you need from any Action, without splicing them together into a cybernetic Rube Goldberg device.

If you must chain Actions, be aware of the following: calling the second Action from the first Action has the same effect as calling the second Action from scratch. If both of your Actions change the properties of a formbean, the changes made by the first Action will be lost because Struts calls the reset() method on the formbean when the second Action is called.

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