自定义标签

Iterate.java#

package customTag;

import java.util.Collection;
import java.util.Iterator;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
/**
 * 迭代
 * @author hzc
 *
 */
public class Iterate extends TagSupport{
	private Object items;
	private String var;
	private Iterator it;
	
	public Object getItems() {
		return items;
	}
	public void setItems(Object items) {
		this.items = items;
	}
	
	public String getVar() {
		return var;
	}
	public void setVar(String var) {
		this.var = var;
	}
	@Override
	public int doAfterBody() throws JspException {
		if(it.hasNext()) {
			//把遍历到的元素用var属性值作为名存放到pageContext中
			this.pageContext.setAttribute(var, it.next());
			return EVAL_BODY_AGAIN;//要求容器重复执行标签主体内容
		}else {
			return SKIP_BODY;
		}
	}
	@Override
	public int doStartTag() throws JspException {
		if(items == null || !(items instanceof Collection)) {
			return SKIP_BODY;
		}
		it = ((Collection)items).iterator();//获取结合迭代器
		if(it.hasNext()) {
			//把遍历到的以第一元素用var属性值作为名存放到pageContext中
			this.pageContext.setAttribute(var, it.next());
			return EVAL_BODY_INCLUDE;//要求容器执行标签体内容
		}else {
			return SKIP_BODY;//如果集合中没有元素就跳过标签体
		}
	}
	

}

TagDemo2.java(小写转大写)#

package customTag;

import java.io.IOException;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
 * 把主体返回的内容转换成大写的自定义标签使用示例
 * 为什么要用BodyTagSupport实例的getPreviousOut()方法来获取JspWriter实例，而不是直接从BodyContent实例中调用getEnclosingWriter()来获取？
 * 这是因为自定义标签有可能会嵌套到其他标签中使用，这时每个标签都会有自己的BodyContent实例，每个内层标签处理类要通过getPreviousOut方法来获取上一层标签处理类的输出对象，这样每个标签的返回内容才能最终通过顶层输出对象写到响应中。
 * @author hzc
 *
 */
public class TagDemo2 extends BodyTagSupport{
	
	private int count = 1; //要循环的次数，默认为1

	public int getCount() {
		return count;
	}

	public void setCount(int count) {
		this.count = count;
	}

	@Override
	public int doAfterBody() throws JspException {
		if(count > 0) {
			//以文本的方式获取标签主体的内容
			String bodyString = getBodyContent().getString();
			try {
				if(bodyString != null) {
					//获取外层标签的输出流对象
					JspWriter out = getPreviousOut();
					out.print(bodyString.toUpperCase());
				}
				bodyContent.clearBody(); //清楚缓存的标签主体内容
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			count--;
			return EVAL_BODY_AGAIN; //继续执行标签主体内容
		}else {
			count = 1;
			return SKIP_BODY;
		}
	}
	
	

}

MySimpleTag.java#

package customTag;

import java.io.IOException;
import java.io.StringWriter;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.JspFragment;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class MySimpleTag extends SimpleTagSupport{
	private int count = 1;
	
	public int getCount() {
		return count;
	}
	public void setCount(int count) {
		this.count = count;
	}
	@Override
	public void doTag() throws JspException, IOException {
		//获取页面输出流
		JspWriter out = this.getJspContext().getOut();
		String str = invokeBody();
		for(int i = 0;i<count;i++) {
			out.println(str.toUpperCase());
		}
	}
//	获取标签主体返回内容
	protected String invokeBody() throws JspException{
		//获取代表该标签主体的JspFragment实例
		JspFragment body = getJspBody();
		StringWriter sw = new StringWriter();
		try {
			if(body != null) {
				//执行标签主体片段，把返回的内容写到字符流中
				//若只想输出标签主体的生成内容，可以使用null参数调用invoke()方法
				body.invoke(sw);
			}
		} catch (JspException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return sw.toString();  //以字符串的形式返回该缓冲区的当前值
		
	}
	

}

iterate.tld#

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN" "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd" >
<taglib>
  <tlib-version>tlib-version</tlib-version>
  <jsp-version>2.0</jsp-version>
  <short-name>short-name</short-name>
  <uri>http://www.hzc.com/tag/iterate</uri>
  <tag>
    <name>iterate</name>
    <tag-class>customTag.Iterate</tag-class>
    <body-content>JSP</body-content>
    <attribute>
    	<name>items</name>
<!--     		此属性是必要的 -->
    	<required>true</required>
<!--     	属性值可以在JSP运行时期动态产生 -->
    	<rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
    	<name>var</name>
    	<required>true</required>
    	<rtexprvalue>true</rtexprvalue>
    </attribute>
    
  </tag>
  <tag>
  	<name>toUpperCase</name>
    <tag-class>customTag.TagDemo2</tag-class>
    <body-content>JSP</body-content>
    
    <attribute>
    	<name>count</name>
    	<required>false</required>
    	<rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
  <tag>
  	<name>SimpleUpperCase</name>
    <tag-class>customTag.MySimpleTag</tag-class>
<!--     主体内容只能是empty、scriptless、tagdeoedent之一 -->
    <body-content>scriptless</body-content>
    
    <attribute>
    	<name>count</name>
    	<required>false</required>
    	<rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
  
</taglib>

web.xml#

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1">
  <display-name>jspdemo</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <jsp-config>
  	<taglib>
  		<taglib-uri>http://www.hzc.com/tag/iterate</taglib-uri>
  		<taglib-location>/WEB-INF/tlds/iterate.tld</taglib-location>
  	</taglib>
  	
  	<taglib>
  		<taglib-uri>http://www.hzc.com/ELFunction</taglib-uri>
  		<taglib-location>/WEB-INF/tlds/ELFunction.tld</taglib-location>
  	</taglib>
  </jsp-config>
</web-app>

iterate.jsp#

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://www.hzc.com/tag/iterate" %>
<%@ page import="java.util.*" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<%
		List<String> list = new ArrayList<String>();
		list.add("hzc");
		list.add("zzl");
		pageContext.setAttribute("list", list);
	%>
	<h2>迭代</h2>
	<c:iterate items="${list }" var="item">${item }<br></c:iterate>
	<c:toUpperCase count="3">hzc<br></c:toUpperCase>
	<c:SimpleUpperCase count="4">zzl<br></c:SimpleUpperCase>
	
</body>
</html>