自定义JSP标签实现-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_45105634/article/details/96510125

1.标签语言特点

<开始标签属性=“属性值”>标签体</结束标签>

2.三大类标签

2.1 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

2.2 控制标签 if /foreach/c
特点是控制的对象是标签体

2.3 数据标签 set
特点是存储数据，没有任何的页面效果

3.自定义标签的开发及使用步骤

3.1 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

3.2 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

3.3 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

4.了解标签的生命周期图

在这里插入图片描述
SKIP_BODY：跳过主体
EVAL_BODY_INCLUDE：计算标签主体内容并[输出]
EVAL_BODY_BUFFERED：计算标签主体内容并[缓存]
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

自定义set、out、if、foreach和select标签

需要导入的jar包
在这里插入图片描述
out实体类

package com.BK_201.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(字符流)
 * @author Felling
 *
 */
public class OutTag extends BodyTagSupport{

	
	private static final long serialVersionUID = 945411142513491165L;
   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实体类

package com.BK_201.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valuer值赋给变量var
 * @author Felling
 *
 */
public class SetTag extends BodyTagSupport{

	
	private static final long serialVersionUID = 1041544171110156814L;
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实体类

package com.BK_201.jsp.tag;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
 * if属于控制标签(页面展示效果依赖的是标签体)
 * 
 * @author Felling
 *
 */
public class IfTag extends BodyTagSupport{
	private static final long serialVersionUID = 2836447501254595341L;
    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实体类

*package com.BK_201.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 = -565443049132898531L;
   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,而非创建一个迭代器
	   Iterator<Object> it=(Iterator<Object>) pageContext.getAttribute("it");
	   if (it.hasNext()) {
		   pageContext.setAttribute(var, it.next());
		   return EVAL_BODY_AGAIN;
	}else {
		return EVAL_PAGE;
	}
}
}

select
自定义select标签应该具备的功能
1、新增查询页面，只要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的展示，以及默认选中指定项

工具包
在这里插入图片描述

package com.BK_201.jsp.tag;
import java.io.IOException;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;

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

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，只要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的展示，以及默认选中指定项
 *   
 * 思考（需要定义那些属性）
 *   1、要往后台传值       ID,name
 *   2、定义数据库存储的对应的标签属性、前台页面展示的标签属性     textKey,textVal
 *   3、定一下拉框的默认值headerTextKey,headTextVal 
 *   4、下拉框需要加载数据   items
 *   5、属性值接受数据库中保存的  value值 	   selectedVal
 *   
 * 属性UI标签
 *   
 * @author QWF
 *
 */
public class SelectTag extends BodyTagSupport {

	private static final long serialVersionUID = 8328355733675214804L;
	private String id;
	private String name;
	private List<Object> items = new ArrayList<>();
	private String textKey;
	private String textVal;
	private String headerTextKey;
	private String headTextVal;
	private String selectedVal;
	
	@Override
	public int doStartTag() throws JspException {
		JspWriter out = pageContext.getOut();
		try {
//			之所以能够在页面上看到下拉框的效果，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 (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return super.doStartTag();
	}
	
	private String toHTML() throws Exception {
		StringBuilder sb = new StringBuilder();
		String value = "";
		String html = "";
		sb.append("<select id='"+id+"' name='"+name+"' >");
		if(!(headerTextKey == null || "".equals(headerTextKey) || headTextVal == null || "".equals(headTextVal))) {
			sb.append("<option selected value='"+headerTextKey+"'>"+headTextVal+"</option>");
		}
//		items=teas,textKey=tid,textVal=tname
		for (Object obj : items) {
//			底层代码
			Field f = obj.getClass().getDeclaredField(textKey);
			f.setAccessible(true);
			value = (String) f.get(obj);
//			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库所存储的值
			if(value.equals(selectedVal)) {
				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 List<Object> getItems() {
		return items;
	}
	public void setItems(List<Object> items) {
		this.items = items;
	}
	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 getHeadTextVal() {
		return headTextVal;
	}
	public void setHeadTextVal(String headTextVal) {
		this.headTextVal = headTextVal;
	}
	public String getSelectedVal() {
		return selectedVal;
	}
	public void setSelectedVal(String selectedVal) {
		this.selectedVal = selectedVal;
	}

}

tld 文件
将每个助手类进行配置

<?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>BK_201 1.1 core library</description>
	<display-name>BK_201 core</display-name>
	<tlib-version>1.1</tlib-version>
	<short-name>c</short-name>
	<uri>/BK_201</uri>

	<tag>
		<!-- 填写的是标签库中的标签名 -->
		<name>demo</name>
		<!-- 标签对应后台助手类 -->
		<tag-class>com.BK_201.jsp.tag.DemoTag</tag-class>
		<!-- 标签类别 -->
		<body-content>JSP</body-content>
		<attribute>
		<!-- 自定义标签中属性 -->
			<name>test</name>
			<!-- 属性值是否必填 -->
			<required>true</required>
			<!-- 是否支持表达式EL表达式/ognl表达式 -->
			<rtexprvalue>false</rtexprvalue>
		</attribute>
	</tag>
	
	
	<tag>
		<name>set</name>
		<tag-class>com.BK_201.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>false</rtexprvalue>
		</attribute>
	</tag>
	
	
	
	<tag>
		<name>out</name>
		<tag-class>com.BK_201.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.BK_201.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.BK_201.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>
	
	
	<tag>
    <name>select</name>
    <tag-class>com.BK_201.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>headTextVal</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <name>selectedVal</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>


</taglib>

页面展示源码

<%@page import="com.BK_201.jsp.entity.Teacher"%>
<%@page import="java.util.List"%>
<%@page import="java.util.ArrayList"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
     <%@ taglib prefix="z" uri="/BK_201" %>
<!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案例2</title>
</head>
<body>
<z:set var="name" value="ls"></z:set>
<z:out value="${name}"></z:out>
<z:if test="true">zl</z:if>
<z:if test="false">ww</z:if>
<%
List list=new ArrayList();
list.add(new Teacher("1","张三"));
list.add(new Teacher("2","李四"));
list.add(new Teacher("3","往往i"));
list.add(new Teacher("4","找了"));
list.add(new Teacher("5","圣骑"));
pageContext.setAttribute("teas", list);
%>
<z:foreach items="${teas }" var="t">
${t.tid },${t.tname }<br>
</z:foreach>
<h2>新增查询页面下拉框</h2>
	<z:select textVal="tname" items="${teas }" textKey="tid"></z:select>
	<z:select headerTextKey="-1" headTextVal="请选择" textVal="tname" items="${teas }" textKey="tid"></z:select>
	<h2>修改页面下拉框</h2>
	<z:select textVal="tname" items="${teas }" textKey="tid"></z:select>
	<z:select headerTextKey="-1" headTextVal="请选择" textVal="tname" items="${teas }" textKey="tid" selectedVal="3"></z:select>
	<z:select headerTextKey="-1" headTextVal="请选择" textVal="tname" items="${teas }" textKey="tid" selectedVal="4"></z:select>

</body>
</html>