Introduction to using instances Based on JSP custom tags

Add a JSP custom tag:

Add a tld file to the WEB-INF folder first
<? Xml version = "1.0" encoding = "UTF-8"?>
<Taglib xmlns = "http://java.sun.com/xml/ns/j2ee" xmlns: xsi = "http://www.w3.org/2001/XMLSchema-instance"
Xsi: schemaLocation = "http://java.sun.com/xml/ns/j2ee web-jsptaglibrary_2_0.xsd"
Version = "2.0">

<Description> myTag </description>
<Display-name> JSTL core </display-name>
<Tlib-version> 1.0 </tlib-version>
<Short-name> cnweb </short-name>
<Uri> http://www.cnweb.cn </uri>

<Tag> <! -- A tag corresponds to a custom tag class -->
<Description> MyTag </description>
<Name> when </name>
<Tag-class> cn. example. when </tag-class>
<Body-content> scriptless </body-content>
<Attribute>
<Name> test </name>
<Required> true </required>
<Rtexprvalue> true </rtexprvalue>
</Attribute>
</Tag>
</Taglib>
Reference rules:
<% @ Taglib uri = "http://www.cnweb.cn" prefix = "cnweb" %>

Define error handling page:

<Error-page>
<Exception-type> java. lang. Exception </exception-type>
<Location>/errors/error. jsp </location>
</Error-page>
<Error-page>
<Error-code> 404 </error-code>
<Location>/errors/error1.jsp </location>
</Error-page>

Custom tag execution process:

SimpleTagSupport

/* The Jsp Engine experiences a simple class, which is instantiated;
* Call setJspContext to pass the page pageContext to the tag processing class;
* Call setParent to pass the parent tag. If no, null is passed.
* Call the setJspBody method to pass the encapsulated label JspFragment to the label processor class.
* The custom tag and doTag () method on the execution page; --> the execution is complete, and the object is destroyed.
*/

JspFragment jf = this. getJspBody ();
Jf. invoke (this. getJspContext (). getOut (); // if not displayed, no processing is performed.

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Public classTagShowOrNotExtends TagSupport {
Public int doStartTag () throws JspException {
Return Tag. EVAL_BODY_INCLUDE; // display the body
// Return Tag. SKIP_BODY; // hide the body
// Tag. EVAL_PAGE; // display page
// Tag. SKIP_PAGE; // hide the page
}}

TagSupport
/* Write a class that implements TagSupport;
* Describe the tag processor class in the tld file (tld File Location: Under the WEB-INF)
* Import and use tags on the jsp page
*
* This class is instantiated when a custom tag is encountered during jsp execution;
* Then run setPageContext () --> setParent () --> doStartTag ()
* If there is a TAG body, the TAG body is generally executed; doEndTag () --> after the entire tag is executed, it is generally executed: release ()
*
* Determines whether the entire jsp page is executed;
* Controls whether a part of the jsp page is executed;
* Control repeated execution of jsp page content;
* Modify jsp page content output;
*/

// After the label body is executed, the method is executed before the doEndTag () method is executed until the method returns IterationTag. SKIP_BODY;
Public int doAfterBody () throws JspException {
Time --;
System. out. println ("repeated" + time );
If (time> 0 ){
Return IterationTag. EVAL_BODY_AGAIN;
} Else
Return IterationTag. SKIP_BODY;
}