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JSP自定义标签

程序员文章站 2022-03-11 11:06:13
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JSP自定义标签

一、基础标签介绍
1. 标签语言特点
<开始标签 属性=“属性值”>标签体</结束标签>

   空标签
   <br/><hr/>

<开始标签></结束标签>
<开始标签/>

ui标签 c:out
特点是显示数据，并且数据不是来源于标签体的，而是来源于jsp标签本身
控制标签 if /foreach
特点是控制的对象是标签体
数据标签 set
特点是存储数据，没有任何的页面效果

2. 自定义标签的开发及使用步骤
2.1 创建一个标签助手类(继承BodyTagSupport)
标签属性必须助手类的属性对应、且要提供对应get/set方法
rtexprvalue
代码演示：

package com.wangjing.jsp.Tag;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;

public class DemoTag extends BodyTagSupport {

	/**
	 * ***的作用是方便对象进行序列化，序列化实际上就是将对象按照特定的规则持久化到硬盘
	 * 反序列化：把硬盘的对象读到内存当中
	 */
	private static final long serialVersionUID = -645661699234557954L;
private String test;
	
	
	public String getTest() {
		return test;
	}

	public void setTest(String test) {
		this.test = test;
	}

	@Override
		public int doStartTag() throws JspException {
			System.out.println(test);
			System.out.println("doStartTag-----------------------");
			return EVAL_BODY_INCLUDE;
		}
	
	@Override
		public int doEndTag() throws JspException {
			System.out.println("doEndTag-------------------------");
			return super.doEndTag();
		}
	
	@Override
		public int doAfterBody() throws JspException {
			System.out.println("doAfterBody----------------------");
			boolean flag = true;
			
			return flag ? EVAL_BODY_AGAIN : EVAL_PAGE;
		}
	
}

2.2 创建标签库描述文件(tld)，添加自定义标签的配置
注：tld文件必须保存到WEB-INF目录或其子目录
2.3 在JSP通过taglib指令导入标签库，并通过指定后缀
访问自定义标签

3. 标签生命周期JSP自定义标签
SKIP_BODY：跳过主体
EVAL_BODY_INCLUDE：计算标签主体内容并[输出]
EVAL_PAGE:计算页面的后续部分
SKIP_PAGE:跳过页面的后续部分
EVAL_BODY_AGAIN:再计算主体一次
二、自定义标签
1. 自定义标签开发步骤
1.1 助手类
1.2 tld
1.3 taglib
2. UI标签
z:out 1
m:select 5

 <h1 value="xxx"></h1>

注1：JspWriter writer = pageContext.getOut();
3. 控制标签
m:if 2
m:forEach 3

<h1 >xxxx </h1>

注1：page(pageContext)|request(…)|session(…)|application(…)
存储和交换数据
B compare
4. 数据标签
m:set 4
数据标签就是用来存储数据的
c:set

  <h1></h1>

ehcache
仿写c标签：
out标签：

package com.wangjing.jsp.Tag;

import java.io.IOException;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;

/**
 * out属于ui标签（需要展示效果，是依靠标签属性展示页面效果）
 * JspWriter
 * @author wj
 *
 */
public class OutTag extends BodyTagSupport {

	private static final long serialVersionUID = -4776951280538816832L;
	private Object value;
	public Object getValue() {
		return value;
	}
	public void setValue(Object value) {
		this.value = value;
	}
	@Override
	public int doStartTag() throws JspException {
		 JspWriter out = pageContext.getOut();
		 try {
			out.print(value);
		} catch (IOException e) {
			e.printStackTrace();
		}
		return super.doStartTag();
	}
}

set标签：

package com.wangjing.jsp.Tag;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;

/**
 * 数据标签（不需要展示内容）
 * 作用：
 * 	是将value赋给变量var
 * @author wj
 *
 */
public class SetTag extends BodyTagSupport {
	private static final long serialVersionUID = -2130898555302253651L;
	private String var;
	private Object value;
	public String getVar() {
		return var;
	}
	public void setVar(String var) {
		this.var = var;
	}
	public Object getValue() {
		return value;
	}
	public void setValue(Object value) {
		this.value = value;
	}
	@Override
	public int doStartTag() throws JspException {
		pageContext.setAttribute(var, value);
		return SKIP_BODY;
	}
}

if标签：

package com.wangjing.jsp.Tag;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;

/**
 * if属于控制标签(页面展示效果依赖于标签体)
 * @author wj
 *
 */
public class IfTag extends BodyTagSupport {
	private static final long serialVersionUID = -8075622033288162446L;
	private boolean test;
	public boolean isTest() {
		return test;
	}
	public void setTest(boolean test) {
		this.test = test;
	}
	@Override
	public int doStartTag() throws JspException {
		return test ? EVAL_BODY_INCLUDE : SKIP_BODY;
	}
}

foreach标签:

package com.wangjing.jsp.Tag;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;

public class ForeachTag extends BodyTagSupport {

	private static final long serialVersionUID = -6048931116591412523L;
	private String var;
	private List<Object> items=new ArrayList<>();
	public String getVar() {
		return var;
	}
	public void setVar(String var) {
		this.var = var;
	}
	public List<Object> getItems() {
		return items;
	}
	public void setItems(List<Object> items) {
		this.items = items;
	}
	@Override
	public int doStartTag() throws JspException {
		Iterator<Object> it = items.iterator();
		pageContext.setAttribute(var, it.next());
		pageContext.setAttribute("it", it);
		return EVAL_BODY_INCLUDE;
	}
	
	@Override
	public int doAfterBody() throws JspException {
		//获取原来状态的迭代器，而非新创建一个迭代器
		Iterator<Object> it = (Iterator<Object>) pageContext.getAttribute("it");
		if(it.hasNext()){
			pageContext.setAttribute(var, it.next());
			pageContext.setAttribute("it", it);
			return EVAL_BODY_AGAIN;
		}else{
			return EVAL_PAGE;
		}
		
	}
}

wangjing.tid:

<?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>wj 1.1 core library</description>
  <display-name>wj core</display-name>
  <tlib-version>1.1</tlib-version>
  <short-name>c</short-name>
  <uri>/wangjing</uri>

   <tag>
    <name>set</name>
    <tag-class>com.wangjing.jsp.Tag.SetTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <name>var</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
     <attribute>
        <name>value</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
  
   <tag>
    <name>out</name>
    <tag-class>com.wangjing.jsp.Tag.OutTag</tag-class>
    <body-content>JSP</body-content>
     <attribute>
        <name>value</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
  
  <tag>
    <name>if</name>
    <tag-class>com.wangjing.jsp.Tag.IfTag</tag-class>
    <body-content>JSP</body-content>
     <attribute>
        <name>test</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
  
   <tag>
    <name>foreach</name>
    <tag-class>com.wangjing.jsp.Tag.ForeachTag</tag-class>
    <body-content>JSP</body-content>
     <attribute>
        <name>var</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>items</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
</taglib>

显示代码：

<%@page import="com.wangjing.jsp.emtity.Teacher"%>
<%@page import="java.util.ArrayList"%>
<%@page import="java.util.List"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@taglib uri="/wangjing" prefix="w" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>jsp第一堂课案例</title>
</head>
<body>
	
  <!--  ui标签	c:out -->
  
   <!-- 数据标签	set -->
	<c:set value="zs" var="name"></c:set>
	 <!--  ui标签	c:out -->
	<c:out value="${name}"></c:out>
	 <!-- 控制标签 if /foreach/c  -->
	<c:if test="true">ls</c:if>
	<c:if test="false">ww</c:if>
	<%
  		List list=new ArrayList();
  	list.add(new Teacher("1","胡"));
  	list.add(new Teacher("2","宇"));
  	list.add(new Teacher("3","飞"));
  	pageContext.setAttribute("teas", list);
  	%>
  	<w:foreach items="${teas}" var="t">
  		${t.tid},${t.tname}<br>
  	</w:foreach>
</body>
</html>

显示结果：
JSP自定义标签

自定义select标签：

package com.wangjing.jsp.Tag;

import java.io.IOException;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
import javax.swing.JEditorPane;

import org.apache.commons.beanutils.PropertyUtils;

/**
 * 自定义select标签应该具备的功能
 * 	1、新增查询页面，只能通过一个标签就可以完成数据的绑定，而并非使用c:foreach去循环绑定数据
 * 	2、修改页面同样通过一个自定义标签完成数据的遍历展示，以及默认选中指定
 * 	
 * 
 * 	思考(需要定义哪些属性)：
 * 		1、要往后台传值  id,name
 * 		2、定义数据库存的对应的属性、前台页面展示的标签属性 textKey,textVal
 * 		3、定义下拉框的默认值  headerTextKey,headerTextVal
 * 		4、下拉框需要加载数据  itmes
 * 		5、属性值接收数据库中保存的value值   selectVal
 * @author wj
 *
 */

public class SelectTag extends BodyTagSupport {
	private static final long serialVersionUID = -1850468059778163175L;
	private String id;
	private String name;
	private String textKey;
	private String textVal;
	private String headerTextKey;
	private String headerTextVal;
	private List<Object> items =new ArrayList<>();
	private String selectVal;
	
	@Override
	public int doStartTag() throws JspException {
		JspWriter out = pageContext.getOut();
		try {
//			之所以能够在页面上看到select下拉框，原因在于后台做了HTML代码的拼接
			out.print(toHTML());
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchFieldException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return super.doStartTag();
	}
	
	private String toHTML() throws NoSuchFieldException, SecurityException, Exception, Exception {
		
		StringBuilder sb=new StringBuilder();
		String value = "";
		String html ="";
		sb.append("<select id='"+id+"' name='"+id+"'>");
		if(!(headerTextKey == null || "".equals(headerTextKey) || headerTextVal==null || "".equals(headerTextVal))) {
			sb.append("<option selected value='"+headerTextKey+"'>"+headerTextVal+"</option>");
		}
		for (Object obj : items) {
//			底层代码
			Field f= obj.getClass().getDeclaredField(textKey);
			f.setAccessible(true);
			value=(String) f.get(obj);
//			sb.append("<option value='"+value+"'></option>");
//			第三方工具包方法
			html=(String) PropertyUtils.getProperty(obj, textVal);
//			考虑如果是修改页面需要下拉框回选数据所存储的值
			if(selectVal == null || "".equals(selectVal)) {
				sb.append("<option value='"+value+"'>"+html+"</option>");
			}else {
				if(value.equals(selectVal)) {
				sb.append("<option selected value='"+value+"'>"+html+"</option>");
				}else {
					sb.append("<option  value='"+value+"'>"+html+"</option>");
				}
			}
		}
		sb.append("</select>");
		return sb.toString();
	}

	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getTextKey() {
		return textKey;
	}
	public void setTextKey(String textKey) {
		this.textKey = textKey;
	}
	public String getTextVal() {
		return textVal;
	}
	public void setTextVal(String textVal) {
		this.textVal = textVal;
	}
	public String getHeaderTextKey() {
		return headerTextKey;
	}
	public void setHeaderTextKey(String headerTextKey) {
		this.headerTextKey = headerTextKey;
	}
	public String getHeaderTextVal() {
		return headerTextVal;
	}
	public void setHeaderTextVal(String headerTextVal) {
		this.headerTextVal = headerTextVal;
	}
	public List<Object> getItems() {
		return items;
	}
	public void setItems(List<Object> items) {
		this.items = items;
	}
	public String getSelectVal() {
		return selectVal;
	}
	public void setSelectVal(String selectVal) {
		this.selectVal = selectVal;
	}
}

wangjing.tld：

<?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>wj 1.1 core library</description>
  <display-name>wj core</display-name>
  <tlib-version>1.1</tlib-version>
  <short-name>c</short-name>
  <uri>/wangjing</uri>

	 <tag>
    <name>select</name>
    <tag-class>com.wangjing.jsp.Tag.SelectTag</tag-class>
    <body-content>JSP</body-content>
     <attribute>
        <name>id</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>name</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>items</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
     <attribute>
        <name>textKey</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>textVal</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>headerTextKey</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
     <attribute>
        <name>headerTextVal</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
     <attribute>
        <name>selectVal</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>
</taglib>

显示页码：

<%@page import="com.wangjing.jsp.emtity.Teacher"%>
<%@page import="java.util.ArrayList"%>
<%@page import="java.util.List"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@taglib uri="/wangjing" prefix="w" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>jsp第二堂课案例</title>
</head>
<body>
<%--  <w:set var="name" value="zs"></w:set>
	<w:out value="${name}"></w:out>
  	<w:if test="true">ls</w:if>
  	<w:if test="false">ww</w:if>  --%>
  	
  	<%
  		List list=new ArrayList();
  	list.add(new Teacher("1","胡"));
  	list.add(new Teacher("2","宇"));
  	list.add(new Teacher("3","飞"));
  	pageContext.setAttribute("teas", list);
  	%>
  	<w:foreach items="${teas}" var="t">
  		${t.tid},${t.tname}<br>
  	</w:foreach>
  	<h2>新增查询页面下拉框</h2>
  	<w:select textVal="tname" items="${teas}" textKey="tid"></w:select>
  	<w:select textVal="tname" items="${teas}" textKey="tid" headerTextKey="-1" headerTextVal="---请选择---"></w:select>
  	<h2>修改页面下拉框</h2>
  	<w:select textVal="tname" items="${teas}" textKey="tid" headerTextKey="-1" headerTextVal="---请选择---" selectVal="3"></w:select>
</body>
</html>

显示结果：

JSP自定义标签

相关标签： 自定义jsp

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