本文介绍了如何开发和解析JSP中的自定义条件标签<c:if>和<c:else>。通过创建ChooseTag、WhenTag和OtherWiseTag类实现逻辑判断，当条件满足时执行相应标签体。示例代码展示了如何在JSP页面中使用这些自定义标签。
开发<c:if><c:else>标签解析及其源代码
if else条件判定：
<c:if>aaaa</c:if> :IfTag.java
<c:else>bbb</c:else> ElseTag.java
共享一个boolean变量
<c:choose> 为父标签写一个标签处理器ChooseTag.java
<c:when test=””></c:when> 标签处理器WhenTag.java
<c:otherwise></c:otherwise> 标签处理器OtherWise.java
</c:choose>
为父标签写一个标签处理器ChooseTag.java：
import java.io.IOException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.JspFragment;
import javax.servlet.jsp.tagext.SimpleTagSupport;
public class ChooseTag extends SimpleTagSupport {
private boolean flag=false;
public boolean isFlag() {
return flag;
}
public void setFlag(boolean flag) {
this.flag = flag;
}
@Override
public void doTag() throws JspException, IOException {
JspFragment jf=this.getJspBody();
jf.invoke(null);
}
}
标签处理器WhenTag.java：
import java.io.IOException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;
public class WhenTag extends SimpleTagSupport {
private boolean test1;
public void setTest1(boolean test1) {
this.test1 = test1;
}
@Override
public void doTag() throws JspException, IOException {
//获取父标签对象
ChooseTag parent=(ChooseTag)this.getParent();
if(test1 && !parent.isFlag()){
//处理该标签体
this.getJspBody().invoke(null);
parent.setFlag(true);
}
}
}
标签处理器OtherWise.java：
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 {
ChooseTag parent=(ChooseTag)this.getParent();
if(!parent.isFlag()){
this.getJspBody().invoke(null);
//将父标签的标志设置为true
parent.isFlag();
}
}
}
标签：
<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<%@ taglib uri="http://www.hbsi.edu.com" prefix="c"%>
<%
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 'TestIf.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
</head>
<body>
<c:choose>
<c:when test1="${user!=null}">aaaaa</c:when>
<c:otherwise>bbbbb</c:otherwise>
</c:choose>
</body>
</html>
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