Add JSP custom tags:

Start by adding an tld file to the WEB-INF folder < ?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 > < ! — one tag tag corresponds to one custom tag 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 the 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 label execution process:

SimpleTagSupport

/* Jsp engine encounters a simple class and instantiates it; * call setJspContext, pass the page pageContext to the tag handling class; * call setParent to pass in the parent; if not, pass null * calls the setJspBody method, passing the wrapped tag body JspFragment to the tag handler class * execute the custom tag on the page, doTag() method; — > When execution is complete, the object is destroyed */

JspFragment jf = this.getJspBody(); jf. invoke (this. getJspContext () getOut ()); // if it is not displayed, it is not processed

--------------------------------------------------------------------

public class tagShowOrNot extends TagSupport { public int doStartTag() throws JspException { return Tag. EVAL_BODY_INCLUDE; / / display body / / return Tag. SKIP_BODY; / / hide body / / Tag. EVAL_PAGE; / / display page / / Tag. SKIP_PAGE; / / hide page }}

TagSupport /* write a class that implements TagSupport; * label processor class is described in tld file (location of tld file: WEB-INF) * import and use tags on the jsp page * * when a custom tag is encountered during the execution of jsp, the class is instantiated first; * then execute method: setPageContext()— > setParent()— > doStartTag() * if there is a tag body, 1 will generally execute the tag body; doEndTag () - > After the entire tag is executed, 1 will normally be executed :release() * * controls whether the entire jsp page is executed; * controls whether part 1 of the jsp page is executed; * control the repeated execution of jsp page contents; * modify jsp page content output; */

// this method executes after the tag body, but before doEndTag(), until the method returns IterationTag.SKIP_BODY; public int doAfterBody() throws JspException { time—; System.out.println (” repeat ”+ time); if (time > 0) { return IterationTag.EVAL_BODY_AGAIN; } else return IterationTag.SKIP_BODY; }