JSP标签案例----开发If-else和单独的if标签

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首先是开发一个if标签，先是实现类

package com.bird.web.tag.example; import java.io.IOException; import javax.servlet.jsp.JspException; import javax.servlet.jsp.tagext.SimpleTagSupport; public class IfTag extends SimpleTagSupport{ private boolean test; public void setTest(boolean test) { this.test = test; } @Override public void doTag() throws JspException, IOException { if(test){ this.getJspBody().invoke(null); } } }
然后是TLD描述文件

<?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 http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd" version="2.0"> <description>A tag library exercising SimpleTag handlers.</description> <tlib-version>1.0</tlib-version> <short-name>Bird</short-name> <uri>/example</uri> <tag> <name>referer</name> <tag-class>com.bird.web.tag.example.RefererTag</tag-class> <body-content>empty</body-content> <attribute> <name>site</name> <required>true</required> <rtexprvalue>true</rtexprvalue> </attribute> <attribute> <name>page</name> <required>true</required> <rtexprvalue>true</rtexprvalue> </attribute> </tag> <tag> <name>if</name> <tag-class>com.bird.web.tag.example.IfTag</tag-class> <body-content>scriptless</body-content> <attribute> <name>test</name> <required>true</required> <rtexprvalue>true</rtexprvalue> </attribute> </tag> <tag> <name>chose</name> <tag-class>com.bird.web.tag.example.ChoseTag</tag-class> <body-content>scriptless</body-content> </tag> <tag> <name>when</name> <tag-class>com.bird.web.tag.example.WhenTag</tag-class> <body-content>scriptless</body-content> <attribute> <name>test</name> <required>true</required> <rtexprvalue>true</rtexprvalue> </attribute> </tag> <tag> <name>otherwise</name> <tag-class>com.bird.web.tag.example.OtherWiseTag</tag-class> <body-content>scriptless</body-content> </tag> </taglib>
然后使用

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8" contentType="text/html; charset=UTF-8"%> <%@taglib uri="/example" prefix="c" %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>开发IF标签</title> </head> <body> <% request.setAttribute("user","aaaa"); %> <c:if test="${user==null }"> aaaaaa </c:if> <c:if test="${user!=null }"> bbbbb </c:if> </body> </html>
下面是开发嵌套标签，if--else 标签

首先还是三个实现类

package com.bird.web.tag.example; import java.io.IOException; import javax.servlet.jsp.JspException; import javax.servlet.jsp.tagext.SimpleTagSupport; public class ChoseTag extends SimpleTagSupport { private boolean isDo; public boolean isDo() { return isDo; } public void setDo(boolean isDo) { this.isDo = isDo; } @Override public void doTag() throws JspException, IOException { this.getJspBody().invoke(null); } }
然后是when标签

package com.bird.web.tag.example; import java.io.IOException; import javax.servlet.jsp.JspException; import javax.servlet.jsp.tagext.SimpleTagSupport; public class WhenTag extends SimpleTagSupport{ private boolean test; public void setTest(boolean test) { this.test = test; } @Override public void doTag() throws JspException, IOException { ChoseTag parent = (ChoseTag) this.getParent(); if(test && parent.isDo()==false){ this.getJspBody().invoke(null); parent.setDo(true); } } }
然后是else

package com.bird.web.tag.example; import java.io.IOException; import javax.servlet.jsp.JspException; import javax.servlet.jsp.tagext.SimpleTagSupport; public class OtherWiseTag extends SimpleTagSupport{ @Override public void doTag() throws JspException, IOException { ChoseTag parent = (ChoseTag) this.getParent(); if(parent.isDo() == false){ this.getJspBody().invoke(null); parent.setDo(true); } } }最后是使用<%@ page language="java" import="java.util.*" pageEncoding="UTF-8" contentType="text/html; charset=UTF-8"%> <%@taglib uri="/example" prefix="c" %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>开发嵌套标签，if-else</title> </head> <body> <%session.setAttribute("user","aaa"); %> <c:chose> <span style="white-space: pre;"> </span><c:when test="${user==null }">aaaaaaaaaaaa</c:when> <span style="white-space: pre;"> </span><c:otherwise>bbbbbbbbbbbb</c:otherwise> </c:chose> </body> </html>

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