Struts里的html:Cancel标签是在Form中经常运用的一个标签主要功能就是cancel当前Form一般写法如下
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<html:cancel>
<bean:message key=createusercancelbutton/>
</html:cancel>
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这个标签将生成如下的HTML代码
<input type=submit name=orgapaclCANCEL value=返回 onclick=bCancel=true;>
bCancel=true是一段javascriptbCancel是在使用Struts的Validator时Struts自动为我们加的一段Javascript代码里的一个变量
这段Javascript简略摘要如下
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<script type=text/javascript language=Javascript>
<! Begin
var bCancel = false;
function validateCreateUserForm(form) {
if (bCancel)
return true;
else
return validateMaxLength(form) && validateRequired(form) && validateMinLength(form);
}
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由上可以看到这个bCancel=true时Javascript将自动将表单提交（return true）也就是说如果我们在后台Action的代码里
没有对这个Cancel动作写特定代码的话这个Cancel标签产生的效果和submit按钮产生的动作完全一致！！（因为这个按钮的
type也等于submit）
这一点需要非常的注意！所以一般来说我们在Action类的execute方法里面会加上如下的一段代码来处理这个Cancel动作
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// Was this transaction cancelled?
if (isCancelled(request)) {
return (mappingfindForward(createusersuccess));
}
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有了以上的代码Cancel动作就有了相应的处理代码转到相关的页面了
本来事情已经解决但本着对Struts源码研究的精神我们还需要对以上代码研究一下
OK让我们来看一下isCancelled这个方法在什么地方被定义了内容是什么？
首先发现这个方法被定义在Action类里面代码如下
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/**
* <p>Returns <code>true</code> if the current forms cancel button was
* pressed This method will check if the <code>GlobalsCANCEL_KEY</code>
* request attribute has been set which normally occurs if the cancel
* button generated by <strong>CancelTag</strong> was pressed by the user
* in the current request If <code>true</code> validation performed
* by an <strong>ActionForm</strong>s <code>validate()</code> method
* will have been skipped by the controller servlet</p>
*
* @param request The servlet request we are processing
* @see orgapaclCancelTag
*/
protected boolean isCancelled(HttpServletRequest request) {
return (requestgetAttribute(GlobalsCANCEL_KEY) != null);
}
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哦原来是在request对象中查找GlobalsCANCEL_KEY这个key值是否绑定了一个对象如果是那么就代表按下Cancel按钮后
Struts会在request对象中绑定一个对象并以这个key值来命名
那Struts是在什么地方绑定了这个对象呢？很自然的让我们从头找起
从ActionServlet的process方法开始找起历经多次方法调用终于找到了根源原来是在RequestProcessorjava中代码如下
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/**
* <p>Process an <code>HttpServletRequest</code> and create the
* corresponding <code>HttpServletResponse</code></p>
*
* @param request The servlet request we are processing
* @param response The servlet response we are creating
*
* @exception IOException if an input/output error occurs
* @exception ServletException if a processing exception occurs
*/
public void process(HttpServletRequest request
HttpServletResponse response)
throws IOException ServletException {
//省略代码若干
// Process any ActionForm bean related to this request
ActionForm form = processActionForm(request response mapping);
//答案就在这个processPopulate方法中
processPopulate(request response form mapping);
if (!processValidate(request response form mapping)) {
return;
}
/**
* Populate the properties of the specified ActionForm instance from
* the request parameters included with this request In addition
* request attribute <code>GlobalsCANCEL_KEY</code> will be set if
* the request was submitted with a button created by
* <code>CancelTag</code>
*
* @param request The servlet request we are processing
* @param response The servlet response we are creating
* @param form The ActionForm instance we are populating
* @param mapping The ActionMapping we are using
*
* @exception ServletException if thrown by RequestUtilspopulate()
*/
protected void processPopulate(HttpServletRequest request
HttpServletResponse response
ActionForm form
ActionMapping mapping)
throws ServletException {
if (form == null) {
return;
}
// Populate the bean properties of this ActionForm instance
if (logisDebugEnabled()) {
logdebug( Populating bean properties from this request);
}
formsetServlet(thisservlet);
formreset(mapping request);
if (mappinggetMultipartClass() != null) {
requestsetAttribute(GlobalsMULTIPART_KEY
mappinggetMultipartClass());
}
RequestUtilspopulate(form mappinggetPrefix() mappinggetSuffix()
request);
// Set the cancellation request attribute if appropriate
if ((requestgetParameter(ConstantsCANCEL_PROPERTY) != null) ||
(requestgetParameter(ConstantsCANCEL_PROPERTY_X) != null)) {
requestsetAttribute(GlobalsCANCEL_KEY BooleanTRUE);
}
}
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OK看最后几行代码Struts从request中取得ConstantsCANCEL_PROPERTY这个参数如果这个参数不为空那么他就将
TRUE这个对象以GlobalsCANCEL_KEY为key值放到了request对象中
至于这个ConstantsCANCEL_PROPERTY这个值是什么现在都可以猜到了显然就是html:Cancel这个标签生成的HTML代码
中Cancel这个按钮的名称嘛！查了一下果然是
<input type=submit name=orgapaclCANCEL value=返回 onclick=bCancel=true;>
而ConstantsCANCEL_PROPERTY这个值就是orgapaclCANCEL
