jsp自定义标签

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
控制标签
数据标签

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

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

                                SKIP_BODY

3.1 实例化标签助手类->doStartTag()------------->doEndTag()
//主要用开发简单标签

                                  EVAL_BODY_INCLUDE        SKIP_BODY

3.2 实例化标签助手类->doStartTag()------------->doAfterBody---------------->doEndTag()…
EVAL_BODY_AGAIN

3.3 …

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
备注：1、标签库的运作离不开tld文件 。 2、标签库的标签是定义在tld中的tag标签内（助手类）

4.实践

set助手

package com.likang.jsp;

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

public class SetTag extends BodyTagSupport{

	private static final long serialVersionUID = -6620809487950787524L;

	private String var;
	private String value;
	public String getVar() {
		return var;
	}
	public void setVar(String var) {
		this.var = var;
	}
	public String getValue() {
		return value;
	}
	public void setValue(String value) {
		this.value = value;
	}
	
	@Override
	public int doStartTag() throws JspException {
		// TODO Auto-generated method stub
		pageContext.setAttribute(var, value);
		return SKIP_BODY;
	}
}

out助手

package com.likang.jsp;

import java.io.IOException;

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

public class OutTag extends BodyTagSupport{

	private static final long serialVersionUID = 7607395783929157755L;

	
	private String value;


	public String getValue() {
		return value;
	}


	public void setValue(String value) {
		this.value = value;
	}
	
	@Override
	public int doStartTag() throws JspException {
		// TODO Auto-generated method stub
		JspWriter out = pageContext.getOut();
		try {
			out.print(value);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return SKIP_BODY;
	}
}

if助手

package com.likang.jsp;

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

public class IfTag extends BodyTagSupport{

	private static final long serialVersionUID = 1L;

	private boolean test;

	public boolean isTest() {
		return test;
	}

	public void setTest(boolean test) {
		this.test = test;
	}
	
	@Override
	public int doStartTag() throws JspException {
		// TODO Auto-generated method stub
		return test ? EVAL_BODY_INCLUDE :SKIP_BODY;
	}
	
}

foreach助手

package com.likang.jsp;

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

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyTagSupport;
/**
 * c:foreach
 * var 指针
 * items 指的是需要遍历的集合对象
 * <c:foreach var="stu" items="stus">
 * ${stu.name}...
 * <c/foreach}
 * @author Hasee
 *
 */
public class ForeachTag extends BodyTagSupport{

	private static final long serialVersionUID = 1L;

	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();
			//默认指针存放的位置是没有指向对象的，现在需要指向对象，那么需要指针下移
			pageContext.setAttribute(var, it.next());
			//因为集合中元素较多，那么指针需要循环的向下移动，那么我们需要将迭代器保存，用于下一次指针下移所用
			pageContext.setAttribute("it", it);
			
		return EVAL_BODY_INCLUDE;
	}
	@Override
	public int doAfterBody() throws JspException {
		// TODO Auto-generated method stub
	//获取已经保存了的迭代器
		Iterator<Object> it= (Iterator<Object>) pageContext.getAttribute("it");
		if(it.hasNext()) {
			//指针下移指向新的元素
			pageContext.setAttribute(var,it.next());
			//再保存正在使用的迭代器
			pageContext.setAttribute("it", it);
			return EVAL_BODY_AGAIN;
		}
		return EVAL_PAGE;
	}
	
}

select助手

package com.likang.jsp;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
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.BeanUtils;

import com.sun.org.apache.xml.internal.serializer.ToHTMLSAXHandler;
import com.sun.org.apache.xml.internal.serializer.ToHTMLStream;

/**
 * <select id='' name=''>
 * <option value='' selected></option>
 * </select>
 * 查询维度:下拉列表
 * 修改页面：下拉列表   数据回显
 * 
 * 
 * 1。id，name
 * 2,数据源，存入数据库中值textKey,展示列textVal
 * 3，加入属性（默认的头部属性值，默认的展示列值）
 * 4，加入属性，能够实现数据回显的功能selectdVal
 * @author Hasee
 *
 */
public class SelectTag extends BodyTagSupport{

	private static final long serialVersionUID = 1L;

	private String id;
	private String name;
	private List<Object> items=new ArrayList<Object>();
	
	private String textKey;
	private String textVal;
	private String headTextKey;
	private String headTextVal;
	private String selectedVal;
	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 getHeadTextKey() {
		return headTextKey;
	}
	public void setHeadTextKey(String headTextKey) {
		this.headTextKey = headTextKey;
	}
	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;
	}
	
	@Override
	public int doStartTag() throws JspException {
		JspWriter out = pageContext.getOut();
		try {
			out.write(toTHML());
		} catch (Exception e) {
			// TODO: handle exception
		}
		return super.doStartTag();
	}
	/**
	 * 拼接出下拉列表对应的select的html代码
	 * @return
	 * @throws NoSuchMethodException 
	 * @throws InvocationTargetException 
	 * @throws IllegalAccessException 
	 * @throws SecurityException 
	 * @throws NoSuchFieldException 
	 */
	private String toTHML() throws IllegalAccessException, InvocationTargetException, NoSuchMethodException, NoSuchFieldException, SecurityException {
		// TODO Auto-generated method stub
		StringBuffer sb=new StringBuffer();
		sb.append("<select id='"+id+"' name='"+name+"'>");
		
		if(!(headTextKey==null || "".equals(headTextKey)  ||  headTextVal==null ||  headTextVal.equals(""))) {
			sb.append("<option value='"+headTextKey+"' selected>"+headTextVal+" </option>   ");
		}
		String val;
		String html;
		for (Object obj : items) {
			//让学生id存入数据库，让学生的名字展示
			Field declaredField = obj.getClass().getDeclaredField(textKey);
			declaredField.setAccessible(true);
			val =(String) declaredField.get(obj);
			html=BeanUtils.getProperty(obj, textVal);
			
			if(val.equals(selectedVal)) {
				sb.append("<option value='"+val+"' selected>"+html+" </option>");
				
			}else {
				sb.append("<option value='"+val+"'  >"+html+"</option> ");
			}
		}
		
		sb.append("</select>");
		return sb.toString();
	}
	
	
}

学生实体类

package com.likang.jsp;

public class Student {
	private String sid;

	private String sname;

	public Integer age;

	public Student() {
		super();
		System.out.println("调用无参构造方法创建了一个学生对象");
	}

	public Student(String sid) {
		super();
		this.sid = sid;
		System.out.println("调用带一个参数的构造方法创建了一个学生对象");
	}

	public Student(String sid, String sname) {
		super();
		this.sid = sid;
		this.sname = sname;
		System.out.println("调用带二个参数的构造方法创建了一个学生对象");
	}

	@SuppressWarnings("unused")
	private Student(Integer age) {
		System.out.println("调用Student类私有的构造方法创建一个学生对象");
		this.age = age;
	}

	public String getSid() {
		return sid;
	}

	public void setSid(String sid) {
		this.sid = sid;
	}

	public String getSname() {
		return sname;
	}

	public void setSname(String sname) {
		this.sname = sname;
	}

	public void hello() {
		System.out.println("你好！我是" + this.sname);
	}

	public void hello(String name) {
		System.out.println(name + "你好！我是" + this.sname);
	}

	@SuppressWarnings("unused")
	private Integer add(Integer a, Integer b) {
		return new Integer(a.intValue() + b.intValue());
	}
}

tld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>zking 1.1 core library</description>
	<display-name>zking core</display-name>
	<tlib-version>1.1</tlib-version>
	<short-name>z</short-name>
	<uri>/lk</uri>
	
	<tag>
	<!-- 标签库中的标签(类似c:set  c:out的定义) -->
	<name>set</name>
	<!-- 是标签运行的具体代码,也就是助手类,下面填写的是助手类的全路径名 -->
	<tag-class>com.likang.jsp.SetTag</tag-class>
	<body-content>JSP</body-content>
	<attribute>
	<!-- 该标签的属性 -->
	<name>var</name>
	<!-- 该属性是否必填 -->
	<required>true</required>
	<!-- 是否支持表达式 -->
	<rtexprvalue>false</rtexprvalue>
	</attribute>
	<attribute>
	<name>value</name>
	<required>true</required>
	<rtexprvalue>true</rtexprvalue>
	</attribute>
	</tag>
	
	
	
	<tag>
	<name>out</name>
	<tag-class>com.likang.jsp.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.likang.jsp.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.likang.jsp.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.likang.jsp.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>headTextKey</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>false</rtexprvalue>
	</attribute>
	
	</tag>
	
	
	
</taglib>

jsp页面

<%@page import="com.likang.jsp.Student"%>
<%@page import="java.util.ArrayList"%>
<%@page import="java.util.List"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
    <%@ taglib  uri="/lk"  prefix="x"%>
<!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=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<x:set var="name" value="无极剑圣"></x:set>
<x:out value="${name}"></x:out>

<x:if test="true">你好</x:if>
<x:if test="false">去世</x:if>

<%
List list=new ArrayList();
list.add(new Student("s001","无极剑圣"));
list.add(new Student("s004","无双剑姬"));
list.add(new Student("s003","暗裔剑魔"));
list.add(new Student("s002","疾风剑豪"));
request.setAttribute("stus", list);
%>
<br>
<x:foreach items="${stus }" var="stu">
${stu.sid },${stu.sname}<br>
</x:foreach>


<x:select textVal="sname" selectedVal="s004" headTextKey="-1" headTextVal="请选择" items="${stus }" textKey="sid"></x:select>

</body>
</html>

结果如下