Struts Tag Library in Java: Enhancements and Internationalizatio...

作者：friendcn
日期：2001-2-22 12:50:46
Page changes
The following are the list of changes that occurred using the Struts tag library: 

Imports
<%@ taglib uri="/WEB-INF/struts.tld" prefix="struts" %>
 
The <%@page import? for Java has been replaced by <%@ taglib uri? for the Struts tag library.


Text
<struts:message key="join.title"/>
 
The resource property file contains the text for join.title. In this example, ApplicationResources property file contains the name-value pair. This makes string review and changes for internationalization easier.


Errors
<form:errors/>
 
ActionServlet or ActionForm builds the error message to display. These error messages can also be contained in the property file. ApplicationResources also provides a way of formatting the error by setting error.header and error.footer.


HTML Form
<form:form action="join.do" focus="email" >
 

JSP <form> tags and attributes replace HTML <form> tags and attributes. <form action="join.jsp" name="join"> has changed to <form:form action="join.do" focus="email" >. 
HTML <input> tag has been replaced by <form:text/>. 
HTML <submit> tag has been replaced by <form:submit/>. 

Model -- Session state
JoinForm subclasses ActionForm and contains the form data. The form data in this example is simply the e-mail address. I have added a setter and getter for the e-mail address for the framework to access. For demonstration purposes, I overwrote the validate() method and used the error tracking feature of Struts. Struts will create JoinForm and set the state information.

Model -- Business logic 
As we discussed earlier, Action is the interface between the Controller and the actual business object. JoinAction wraps the calls to the business.jar that was originally in join.jsp. The perform() method for JoinAction is displayed in Listing 5. 

Listing 5. - JoinAction.perform()
public ActionForward perform(ActionMapping mapping,
                             ActionForm form,
                             HttpServletRequest request,
                             HttpServletResponse response)
                             throws IOException, ServletException {
    // Extract attributes and parameters we will need
    JoinForm joinForm = (JoinForm) form;
    String email = joinForm.getEmail();

    ActionErrors errors = new ActionErrors();

    // store input....
    try {
        business.db.MailingList.AddEmail(email);
    } catch (Exception e) {
        // log, print stack


        // display error back to user
        errors.add("email",new ActionError("error.mailing.db.add"));
    }