Jakarta Struts Cookbook

9.1. Simplifying Exception Processing in an Action

Problem

You want to reduce the number of try . . . catch blocks within your Action classes.

Solution

Remove the exception-handling code from your Action, and define global and local exception handlers in your struts-config.xml file, as shown in Example 9-1.

Example 9-1. Global and local exception handling (partial)

...
<global-exceptions>
    <exception key="error.unknown.user" 
              type="com.oreilly.strutsckbk.ch09.UnknownUserException"
              path="/securityError.jsp"/>    
</global-exceptions>
...
<action-mappings>
    <action    path="/Login"
               type="com.oreilly.strutsckbk.ch09.LoginAction"
              scope="request"
               name="LoginForm"
            validate="true"
              input="/login.jsp">
        <exception key="error.password.match" 
                  type="com.oreilly.strutsckbk.ch09.PasswordMatchException">
        <forward name="success" path="/login_success.jsp"/>
    </action>
...

Discussion

Prior to Struts 1.1, the handling of exceptions was left to the devloper's devices. Exceptions returned from calls to the business layer from an Action had to be handled individually in your code. Because the perform( ) method of Struts 1.0 only allowed you to throw IOException and ServletException, you didn't have much choice in the matter:

public ActionForward perform( ActionMapping mapping, 
                              ActionForm form,
                              HttpServletRequest request, 
                              HttpServletResponse response)
    throws IOException, ServletException { ...

Any checked exception thrown within the body of perform() had to be caught and handled. In some cases, it was appropriate to catch ...