Great stuff... Thx <- waiting for Tip #3
Daniel -----Original Message----- From: Galbreath, Mark [mailto:[EMAIL PROTECTED]] Sent: Friday, May 31, 2002 7:40 PM To: 'Struts Users Mailing List' Subject: RE: [Struts Tips] #2 - Use DispatchAction to organize related operations Way excellent response, Ted - thanks for the knowledge xfer. This is really useful stuff! Mark -----Original Message----- From: Ted Husted [mailto:[EMAIL PROTECTED]] Sent: Friday, May 31, 2002 7:12 AM Any software application is defined by the things it can do for you. In a Struts Web application, the things an application does is usually defined by its action-mapping elements. An action-mapping is designed to be the target of an HTML form, and is often used with hyperlinks as well. Each action-mapping can specify a Struts Action class as its handler. In larger applications, developers can find themselves managing dozens or even hundreds of Action classes. In practice, many of these Action classes handle related operations, often evidenced by their name. A package might include separate RegCreate, RegSave, and RegDelete Actions, which just perform different operations on the same RegBean object. Since all of these operations are usually handled by the same JSP page, it would be handy to also have them handled by the same Struts Action. A very simple way to do this is to have the submit button modify a field in the form which indicates which operation to perform. <SCRIPT> function set(target) { document.forms[0].dispatch.value=target; } </SCRIPT> <html:hidden property="dispatch" value="error"/> <html:submit onclick="set('save');">SAVE</html:submit> <html:submit onclick="set('create');">SAVE AS NEW</html:submitl> <html:submit onclick="set('delete);">DELETE</html:submit> Then, in the Action you can setup different methods to handle the different operations, and branch to one or the other depending on which value is passed in the dispatch field. String dispatch = myForm.getDispatch(); if ("create".equals(dispatch)) { ... if ("save".equals(dispatch)) { ... The Struts Dispatch Action is designed to do exactly the same thing, but without messy branching logic. The base perform method will check a dispatch field for you, and invoke the indicated method. The only catch is that the dispatch methods must use the same signature as perform. This is a very modest requirement, since in practice you usually end up doing that anyway. To convert an Action that was switching on a dispatch field to a DispatchAction, you simply need to create methods like this public ActionForward create(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { ... public ActionForward save(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { ... Cool. But do you have to use a property named dispatch? No, you don't. The other step is to specify the name of of the "dispatch" property as the "parameter" property of the action-mapping. So a mapping for our example might look like this: <action path="/reg/dispatch" type="app.reg.RegDispatch" name="regForm" scope="request" validate="true" parameter="dispatch"/> // Which parameter to use If you wanted to use the property "o" instead, as in o=create, you would change the mapping to <action path="/reg/dispatch" type="app.reg.RegDispatch" name="regForm" scope="request" validate="true" parameter="o"/> // Look for o=dispatchMethod Again, very cool. But why use a JavaScript button in the first place? Why not use several buttons named "dispatch" and use the values to specify the operation. You can, but the value of the button is also its label. This means if the page designers want to label the button something different, they have to coordinate with the Action programmer. Worse, localization becomes virtualy impossible. If you prefer not to use JavaScript buttons, you can use the DispatchLookup Action instead. This works much like the DispatchAction, but requires more setup. We'll explore the DispatchLookup Action in Tip #3. HTH, Ted. --- Struts Tips premiere twice weekly on the MVC-Programmers List. To subscribe, visit BaseBean Engineering < http://www.basebeans.com >. An archive of past tips, like this one, is available at < http://jguru.com/faq/subtopic.jsp?topicID=893704 >. About Ted. Ted Husted is an active Struts Committer. He also moderates the Struts mailing list and the JGuru Struts FAQ. Copyright Ted Husted 2002. 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