java:tag 自定义标签应用

时间：2023-06-28 09:06:20

一，tag类

1.1 TagMy标签类，格式化当前日期并输出  
package com.dkt.tag;

import java.io.IOException;

import java.text.SimpleDateFormat;

import java.util.Date;

import javax.servlet.jsp.JspException;

import javax.servlet.jsp.JspWriter;

import javax.servlet.jsp.tagext.TagSupport;

/*

 * doStartTag()               SKIP_BODY执行doEndTag()跳过标签体

 *                                        EVAL_BODY_INCLUDE 执行标签体

 * doAfterBody()            EVAL_BODY_AGAIN 循环执行标签体

 * 								      SKIP_BODY  不执行标签体，执行doEndTag()

 * doEndTag()                SKIP_PAGE   不执行jsp剩余的页面

 * 							          EVAL_PAGE   执行剩余的页面

 *

 */

public class TagMy  extends TagSupport{

	private String format;

	public int doStartTag() {

		SimpleDateFormat simpleDateFormat = new SimpleDateFormat(format);

		String nowdate =  simpleDateFormat.format(new Date());

		JspWriter out = pageContext.getOut();

		try {

			out.print("Hello 世界！！");

			out.print(nowdate);

		} catch (IOException e) {

			e.printStackTrace();

		}

		return super.SKIP_BODY;

	}

	public int doAfterBody() throws JspException {

		return super.doAfterBody();

	}

	public int doEndTag() throws JspException {

		return super.doEndTag();

	}

	public String getFormat() {

		return format;

	}

	public void setFormat(String format) {

		this.format = format;

	}

}　
1.2 ForTag 标签类，自定义<c:foreach>标签，循环输出 
package com.dkt.tag;

import javax.servlet.jsp.tagext.TagSupport;

public class FroTag  extends TagSupport{

	private int start;

	private int end;

	private String var;

	public int doStartTag(){

		System.out.println("doStartTag()"+start);

		if(start<=end){

			pageContext.setAttribute(var, start);

			start++;

			return super.EVAL_BODY_INCLUDE;

		}else {

			return super.SKIP_BODY;

		}

		//执行doAfterBody()

	}

	public int doAfterBody() {

		if(start<=end){

			pageContext.setAttribute(var, start);

			start++;

			System.out.println("doAfterBody()"+start);

			return super.EVAL_BODY_AGAIN;

		}else {

			return super.SKIP_BODY;

		}

	}

	public int doEndTag(){

		System.out.println("doEndTag()"+start);

		return super.EVAL_PAGE;

	}

	public int getStart() {

		return start;

	}

	public void setStart(int start) {

		this.start = start;

	}

	public int getEnd() {

		return end;

	}

	public void setEnd(int end) {

		this.end = end;

	}

	public String getVar() {

		return var;

	}

	public void setVar(String var) {

		this.var = var;

	}

}
1.3 IteratorTag标签类，迭代集合，全部循环输出显示在页面  
package com.dkt.tag;

import java.util.ArrayList;

import java.util.Iterator;

import javax.servlet.jsp.JspException;

import javax.servlet.jsp.tagext.TagSupport;

public class IteratorTag  extends TagSupport{

	private String scope;

	private String var;

	private ArrayList  list = null;

	Iterator it = null;

	public int doStartTag()  {

		/*if (("page").equals(scope)) {

			list = (ArrayList)pageContext.getAttribute(list,pageContext.PAGE_SCOPE);

		}else if(("request").equals(scope)){

			list = (ArrayList)pageContext.getAttribute(list,pageContext.REQUEST_SCOPE);

		}else if(("session").equals(scope)){

			list = (ArrayList)pageContext.getAttribute(list,pageContext.SESSION_SCOPE);

		}else if(("application").equals(scope)){

			list = (ArrayList)pageContext.getAttribute(list,pageContext.APPLICATION_SCOPE);

		}*/

	    it = list.iterator();

		return super.EVAL_BODY_INCLUDE;

	}

	public int doAfterBody()  {

		if (it.hasNext()) {

			Object next = it.next();

			pageContext.setAttribute(var, next);

			return super.EVAL_BODY_AGAIN;

		}else {

			return super.SKIP_BODY;

		}

	}

	public int doEndTag() throws JspException {

		return super.doEndTag();

	}

	public String getScope() {

		return scope;

	}

	public void setScope(String scope) {

		this.scope = scope;

	}

	public String getVar() {

		return var;

	}

	public void setVar(String var) {

		this.var = var;

	}

	public ArrayList getList() {

		return list;

	}

	public void setList(ArrayList list) {

		this.list = list;

	}

}
1.4 QueryTag 标签类，根据表名，查询数据库，并由表格输出到页面  
package com.dkt.tag;

import java.io.IOException;

import java.sql.Connection;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.ResultSetMetaData;

import java.sql.SQLException;

import javax.servlet.jsp.JspException;

import javax.servlet.jsp.JspWriter;

import javax.servlet.jsp.tagext.TagSupport;

import com.dkt.util.DButil;

public class QueryTag  extends TagSupport{

	private String tableName;

	public int doStartTag() {

		DButil dButil = new DButil();

		Connection conn  = null;

		PreparedStatement ps = null;

		ResultSet rs = null;

		conn = dButil.createConn();

		String sql = "select  *  from  "+tableName;

		try {

			ps = conn.prepareStatement(sql);

			ResultSetMetaData rsmd = ps.getMetaData();//得到表结构

			rs = ps.executeQuery();

			JspWriter out = pageContext.getOut();

			out.print("<table border='1px' width='60%'  align='center'><tr>");

			for (int i = 0; i < rsmd.getColumnCount(); i++) {//字段数量

				out.print("<th>"+rsmd.getColumnName(i+1)+"</th>");//字段名字

			}

			out.print("</tr>");

			while(rs.next()){

				out.print("<tr>");

				for (int i = 0; i < rsmd.getColumnCount(); i++) {

					out.print("<td>"+rs.getObject(i+1)+"</td>");

				}

				out.print("</tr>");

			}

			out.print("</table>");

		} catch (SQLException e) {

			e.printStackTrace();

		} catch (IOException e) {

			e.printStackTrace();

		}

		return super.SKIP_BODY;

	}

	public int doAfterBody() throws JspException {

		return super.doAfterBody();

	}

	public int doEndTag() throws JspException {

		return super.doEndTag();

	}

	public String getTableName() {

		return tableName;

	}

	public void setTableName(String tableName) {

		this.tableName = tableName;

	}

}

二，hellotag.tld

文件 hellotag.tld 放在WEB-INF目录下，与web.xml同级

<?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>1.0</tlib-version>

	 <jsp-version>1.2</jsp-version>

	 <short-name>hello</short-name>

	 <uri>hello</uri>

	 <!-- TagMy自定义标签类 -->

	 <tag>

	 	<name>hello</name>    <!-- 标签名 -->

	 	<tag-class>com.dkt.tag.TagMy</tag-class>

	 	<body-content>empty</body-content> <!-- 是否有标签体 jsp/empty -->

	 	<!-- 有属性的标签定义 -->

	 	<attribute>

	 		<name>format</name>

	 		<required>true</required><!-- 表示标签是否必须 -->

	 		<rtexprvalue>true</rtexprvalue><!-- 表示是否可以使用表达式  el/jsp -->

	 	</attribute>

	 </tag>

	 <!-- FroTag -->

	 <tag>

	 		<name>formy</name>

	 		<tag-class>com.dkt.tag.FroTag</tag-class>

	 		<body-content>jsp</body-content>

	 		<attribute>

	 			<name>start</name>

	 			<required>true</required>

	 			<rtexprvalue>true</rtexprvalue>

	 		</attribute>

	 		<attribute>

	 		    <name>end</name>

	 			<required>true</required>

	 			<rtexprvalue>true</rtexprvalue>

	 		</attribute>

	 		<attribute>

	 			<name>var</name>

	 			<required>true</required>

	 			<rtexprvalue>true</rtexprvalue>

	 		</attribute>

	 </tag>

	 <!-- IteraterTag -->

	 	 <tag>

	 		<name>iteratormy</name>

	 		<tag-class>com.dkt.tag.IteratorTag</tag-class>

	 		<body-content>jsp</body-content>

	 		<attribute>

	 			<name>list</name>

	 			<required>true</required>

	 			<rtexprvalue>true</rtexprvalue>

	 		</attribute>

	 		<attribute>

	 		    <name>scope</name>

	 			<required>true</required>

	 			<rtexprvalue>true</rtexprvalue>

	 		</attribute>

	 		<attribute>

	 			<name>var</name>

	 			<required>true</required>

	 			<rtexprvalue>true</rtexprvalue>

	 		</attribute>

	 </tag>

	 <!-- 查询数据库的表并输出 -->

	 <tag>

	 	<name>query</name>

	 	<tag-class>com.dkt.tag.QueryTag</tag-class>

	    <body-content>empty</body-content>

	 	<attribute>

	 		<name>tableName</name>

	 		<required>true</required>

	 		<rtexprvalue>true</rtexprvalue>

	 	</attribute>

	 </tag>

</taglib>

　三，jsp　

index.jsp  开启服务器，直接访问项目下的index.jsp页面即可显示自定义标签

在jsp页面导入自定义标签

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>

<%@page import="com.dkt.entity.UserInfo"%>

<%@ taglib uri="hello" prefix="hello" %>

<%

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 'index.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">

	<!--

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

	-->

  </head>

  <body>

   <hello:hello format="yyyy-MM-dd HH:mm:ss a"/><br/>

   	<hr/>

	formy:<hello:formy end="10" var="item1" start="1">

				${item1 }----

	</hello:formy>

	<hr/>

		iterator：<%

			ArrayList list = new ArrayList();

			list.add(new UserInfo(0,"小白","123456","",""));

			list.add(new UserInfo(1,"小白111","353456","",""));

			list.add(new UserInfo(2,"小白222","532456","",""));

			list.add(new UserInfo(3,"小白333","532356","",""));

			list.add(new UserInfo(4,"小白444","123536","",""));

			request.setAttribute("list",list);

	 %>

	 <hello:iteratormy var="item2" scope="request" list="${list}">

				${item2.name}+++${item2.password }<br/>

	</hello:iteratormy>

	<hr/>

	<hello:query tableName="goods_table2"/>

	<hr>

  </body>

</html>

四，web.xml

<?xml version="1.0" encoding="UTF-8"?>

<web-app version="2.5"

	xmlns="http://java.sun.com/xml/ns/javaee"

	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee

	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

  <welcome-file-list>

  	<welcome-file>index.jsp</welcome-file>

  </welcome-file-list>

</web-app>

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