开发类似sun公司提供的<c:if> <c:else>标签

实现步骤：

第一步：编写一个父标签处理器Choose.java

public class Choose extends SimpleTagSupport {

//标记执行那个标签
private boolean isDo;

public boolean isDo() {
return isDo;
}

public void setDo(boolean isDo) {
this.isDo = isDo;
}
//父标签控制标签体执行
public void doTag() throws JspException, IOException {

getJspBody().invoke(null);
}


}

第二步：编写一个 子标签WhenTag.java 、OtherwithTag.java 类似 if else
public class WhenTag extends SimpleTagSupport {

private boolean test;

public void setTest(boolean test) {
this.test = test;
}

public void doTag() throws JspException, IOException {

Choose parent=(Choose) getParent();
if(test && !parent.isDo())
{
getJspBody().invoke(null);
parent.setDo(true);
}
}
}


public class OtherwithTag extends SimpleTagSupport {

public void doTag() throws JspException, IOException {

Choose parent=(Choose) this.getParent();
if(!parent.isDo())
{
getJspBody().invoke(null);
parent.setDo(true);
}
}
}

第三步：编写一个*.tld文件描述标签处理器


<?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>SimpleTagLibrary</short-name>
<uri>http://www.liyong.nesttag</uri>
<tag>
<description>show client IP</description>
<name>choose</name>
<tag-class>com.liyong.nestTag.Choose</tag-class>
<!-- 标签体不为空 这与传统标签不同 JSP -->
<body-content>scriptless</body-content>
</tag>
<tag>
<description>show client IP</description>
<name>when</name>
<tag-class>com.liyong.nestTag.WhenTag</tag-class>
<body-content>scriptless</body-content>
<attribute>
<name>test</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>

<tag>
<description>show client IP</description>
<name>otherwith</name>
<tag-class>com.liyong.nestTag.OtherwithTag</tag-class>
<body-content>scriptless</body-content>

</tag>
</taglib>

第四步：编写一个jsp 使用标签并且导入自定义标签

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib uri="http://www.liyong.nesttag" prefix="fix" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">

<title>My JSP 'nestTag.jsp' starting page</title>

<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->

</head>

<body>
<br>
<%request.setAttribute("user","user"); %>
<fix:choose>
<fix:when test="${user==null }">
未登陆. <br>
</fix:when>
<fix:otherwith>
welcome用户已经登录. <br>
</fix:otherwith>
</fix:choose>

</body>
</html>

第五步：测试...