jsp开发迭代标签二

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该例注意实现对不同集合的迭代

看例子

第一步：编写标签处理器类
public class ForeachTag2 extends SimpleTagSupport {

private Object items;
private String var;
//把所有的集合和数组转换成单列集合
private Collection collection;

public void setVar(String var) {
this.var = var;
}

public void setCollection(Collection collection) {
this.collection = collection;
}

public void setItems(Object items) {
this.items = items;

if(items==null)
collection=null;
//双列集合
if(items instanceof Collection)
{
collection=(Collection) items;
}
//单列集合
if(items instanceof Map){
Map map=(Map)items;
collection=map.entrySet();
}
//数组不能用instanceof 因为如果是基本数据类型就会报错
if(items.getClass().isArray()){
this.collection=new ArrayList();
int len=Array.getLength(items);
for(int i=0;i<len;i++)
this.collection.add(Array.get(items, i));
}

}

public void doTag() throws JspException, IOException {

if( collection==null) return;
Iterator it=collection.iterator();
while(it.hasNext()){
Object value=it.next();
this.getJspContext().setAttribute(var, value);
this.getJspBody().invoke(null);
}
}
}

第二步：编写标签描述文件

<?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>SimpleTagLibrary</short-name>
 <uri>http://www.liyong.foreach1tag</uri>
 <tag>
 <tag>
 <name>foreach2</name>
 <tag-class>com.liyong.foreach.ForeachTag2</tag-class>
 <body-content>scriptless</body-content>
 <attribute>
 <name>items</name>
 <required>true</required>
 <rtexprvalue>true</rtexprvalue>
 </attribute>
 <attribute>
 <name>var</name>
 <required>true</required>
 <rtexprvalue>false</rtexprvalue>
 </attribute>
</tag>

</taglib>

第三步：编写jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib uri="http://www.liyong.foreach1tag" prefix="foreach"%>
<%
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 'foreach1.jsp' starting page</title>



</head>

<body>  

<foreach:foreach2 items="${list}" var="str">
${str } 
</foreach:foreach2>

______map_____ 
<%
Map map=new HashMap();
map.put("aa","111");
map.put("bb","222");
map.put("cc","333");
request.setAttribute("map",map);
%>
<foreach:foreach2 items="${map}" var="entry">
${entry.key } :${entry.value } 
</foreach:foreach2>

______Integer_____ 
<%
Integer num[]={new Integer(1),new Integer(2),new Integer(3),new Integer(4)};
request.setAttribute("num",num);
 %>
<foreach:foreach2 items="${num}" var="i">
${i } 
</foreach:foreach2>

______String_____ 
<%
String strs[]={"sss","mmm"};
request.setAttribute("strs",strs);
 %>
<foreach:foreach2 items="${strs}" var="str">
${str } 
</foreach:foreach2>
______int_____ 
<%
int num2[]={11,22,33,44};
request.setAttribute("num2",num2);
 %>
<foreach:foreach2 items="${num2}" var="i">
${i }
</foreach:foreach2>
</body>
</html>

第四步：测试...

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jsp开发迭代标签一 | 开发防盗链标签

2012-06-05 14:29
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