在Struts如何使用Validate（）方法

Steps to using validate() in ActionForm:
1.rewrite the method validate() in ActionForm file;
2.in resource file ApplicationResources.properties create error marks;
3.in struts-config.xml, set validate property of <action> to TRUE, and set <message-resources> element to indicate where the resource file locates;
4.in related jsp files, add <html:errors>.

Example:
1.
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LoginActionForm.java
------------------------

...
public ActionErrors validate(ActionMapping mapping, HttpServletRequest request) {
  ActionErrors errors = new ActionErrors();
  // Validate an attribute named "xxx"
  if( getUsername() == null || getUsername().length() < 3 ){
   errors.add("name",new ActionMessage("error.username.required",username));
  }
  if( getPassword() == null || getPassword().length() < 3 ){
   errors.add("pwd",new ActionMessage("error.password.required",password));
  }
  return errors;
 }
...

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2.
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ApplicationResources.properties
---------------------------------

#Username error
error.username.required=<li>Please input your username again!</li>
#Password error
error.password.required=<li>Please input your password again!</li>

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3.
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struts-config.xml
-----------------

<?xml version="1.0" encoding="ISO-8859-1"?>
<!--
     This is a blank Struts configuration file with an example
     welcome action/page and other commented sample elements.

     Tiles and the Struts Validator are configured using the factory defaults
     and are ready-to-use.

     NOTE: If you have a generator tool to create the corresponding Java classes
     for you, you could include the details in the "form-bean" declarations.
     Otherwise, you would only define the "form-bean" element itself, with the
     corresponding "name" and "type" attributes, as shown here.
-->
<struts-config>
  <form-beans>
    <form-bean name="loginActionForm" type="login.loginActionForm"/>
  </form-beans>
  <global-exceptions/>
  <global-forwards>
    <forward name="welcome" path="/Welcome.do"/>
  </global-forwards>
  <action-mappings>
    <action forward="/pages/Welcome.jsp" path="/Welcome"/>
    <action input="/login/login.jsp" name="loginActionForm" path="/loginAction" scope="request" type="login.loginAction" validate="true">
     <forward name="Success" path="/login/main.jsp" />
     <forward name="Fail" path="/login/register.jsp" />
    </action>
  </action-mappings>
  <controller processorClass="org.apache.struts.tiles.TilesRequestProcessor"/>
  <plug-in className="org.apache.struts.tiles.TilesPlugin">
    <set-property property="definitions-config" value="/WEB-INF/tiles-defs.xml"/>
    <set-property property="moduleAware" value="true"/>
  </plug-in>
  <plug-in className="org.apache.struts.validator.ValidatorPlugIn">
    <set-property property="pathnames" value="/WEB-INF/validator-rules.xml,/WEB-INF/validation.xml"/>
  </plug-in>
  <message-resources parameter="ApplicationResources"></message-resources>
</struts-config>

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4.
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login.jsp
----------

...
html:form action="loginAction" method="post">
  Username: <html:text property="username" size="15" />
 <font color="red"><html:errors property="name" /></font>
 <br/>
 <br/>
  Password: <html:password property="password" size="15" />
 <font color="red"><html:errors property="pwd" /></font>
 <br />
 <br />
 <html:submit property="submit" value="Login" />
</html:form>
...

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