JSP系列：(6)JSP进阶-模仿JSTL核心（core）标签库
1、if标签
IfTag.java文件
package com.rk.tag;
import java.io.IOException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.JspFragment;
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
{
//根据test的返回值决定是否输出标签体内容
if(test == true)
{
//JspFragment jspBody = getJspBody();
//jspBody.invoke(null);
this.getJspBody().invoke(null);
}
}
}
.tld文件配置：
<tag> <name>if</name> <tag-class>com.rk.tag.IfTag</tag-class> <body-content>scriptless</body-content> <attribute> <name>test</name> <required>true</required> <rtexprvalue>true</rtexprvalue> <type>boolean</type> </attribute> </tag>
jsp文件
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>控制重复输出标签体内容</title>
</head>
<body>
标签前的内容==========================<br>
<rk:if test="true">条件成立</rk:if> <br/>
<%
boolean value = true;
pageContext.setAttribute("flag", value);
%>
<rk:if test="${flag }">flag为true</rk:if>
<rk:if test="${not flag }">flag为false</rk:if><br/>
标签后的内容========================== <br>
</body>
</html>
2、choose、when、otherwise标签
ChooseTag.java文件
package com.rk.tag;
import java.io.IOException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;
public class ChooseTag extends SimpleTagSupport
{
//不是属性，而是临时变量,用于在子标签中间传递“状态”
private boolean executed = false;
public boolean isExecuted()
{
return executed;
}
public void setExecuted(boolean executed)
{
this.executed = executed;
}
@Override
public void doTag() throws JspException, IOException
{
this.getJspBody().invoke(null);
}
}
.tld文件配置：
<tag> <name>choose</name> <tag-class>com.rk.tag.ChooseTag</tag-class> <body-content>scriptless</body-content> </tag>
WhenTag.java文件
package com.rk.tag;
import java.io.IOException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.JspTag;
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
{
//获取父标签
ChooseTag parent = (ChooseTag)this.getParent();
//如果父标签中的内容还没有执行过，并且当前的判断条件（test）为true，那么就执行输出
if(!parent.isExecuted() && test==true)
{
this.getJspBody().invoke(null);
parent.setExecuted(true);
}
}
}
.tld文件配置：
<tag> <name>when</name> <tag-class>com.rk.tag.WhenTag</tag-class> <body-content>scriptless</body-content> <attribute> <name>test</name> <required>true</required> <rtexprvalue>true</rtexprvalue> <type>boolean</type> </attribute> </tag>
OtherWiseTag.java文件
package com.rk.tag;
import java.io.IOException;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.JspTag;
import javax.servlet.jsp.tagext.SimpleTagSupport;
public class OtherWiseTag extends SimpleTagSupport
{
@Override
public void doTag() throws JspException, IOException
{
//获取父标签
ChooseTag parent = (ChooseTag)this.getParent();
if(!parent.isExecuted())
{
this.getJspBody().invoke(null);
}
}
}
.tld文件配置：
<tag> <name>otherwise</name> <tag-class>com.rk.tag.OtherWiseTag</tag-class> <body-content>scriptless</body-content> </tag>
jsp文件
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@taglib uri="http://www.lsieun.com/rk" prefix="rk" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>控制重复输出标签体内容</title>
</head>
<body>
标签前的内容==========================<br/>
<rk:choose>
<rk:when test="${10>5 }">
10>5
</rk:when>
<rk:when test="${10>6 }">
10>6
</rk:when>
<rk:otherwise>
otherwise
</rk:otherwise>
</rk:choose><br/>
标签后的内容========================== <br/>
</body>
</html>
3、forEach标签
ForEachTag.java文件
package com.rk.tag;
import java.io.IOException;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.SimpleTagSupport;
public class ForEachTag extends SimpleTagSupport
{
private Object items;
private String var;
public void setItems(Object items)
{
this.items = items;
}
public void setVar(String var)
{
this.var = var;
}
@Override
public void doTag() throws JspException, IOException
{
PageContext pageContext = (PageContext)this.getJspContext();
Collection colls = null;
if(items instanceof List){
colls = (List)items;
}
if(items instanceof Map){
Map map = (Map)items;
colls = map.entrySet();
}
for(Object object:colls){
//把每个对象放入域对象中(pageContext)
pageContext.setAttribute(var, object);
//显示标签体内容
this.getJspBody().invoke(null);
}
}
}
.tld文件配置：
<tag> <name>forEach</name> <tag-class>com.rk.tag.ForEachTag</tag-class> <body-content>scriptless</body-content> <attribute> <name>items</name> <required>true</required> <rtexprvalue>true</rtexprvalue> <type>java.lang.Object</type> </attribute> <attribute> <name>var</name> <required>true</required> <rtexprvalue>false</rtexprvalue> <type>java.lang.String</type> </attribute> </tag>
jsp文件
<%@ page language="java" import="java.util.*,com.rk.entity.Student" pageEncoding="utf-8"%>
<%@taglib uri="http://www.lsieun.com/rk" prefix="rk" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>控制重复输出标签体内容</title>
</head>
<body>
标签前的内容==========================<br/>
<%
List<Student> listOfStudent = new ArrayList<Student>();
listOfStudent.add(new Student("lucy",10));
listOfStudent.add(new Student("lily",10));
listOfStudent.add(new Student("tom",10));
pageContext.setAttribute("list", listOfStudent);
Map<String,Student> mapOfStudent = new HashMap<String,Student>();
mapOfStudent.put("100",new Student("lucy",11));
mapOfStudent.put("101",new Student("lily",11));
mapOfStudent.put("102",new Student("tom",12));
pageContext.setAttribute("map", mapOfStudent);
%>
<rk:forEach items="${list }" var="stu">
姓名：${stu.name }--年龄：${stu.age }<br/>
</rk:forEach>
<br/>
<hr/>
<rk:forEach items="${map }" var="entry">
编号：${entry.key}--姓名：${entry.value.name }--年龄：${entry.value.age }<br/>
</rk:forEach>
<br/>
标签后的内容========================== <br/>
</body>
</html>