jsp标签

1、jsp标签

JSP标签也称之为Jsp Action(JSP动作)元素，它用于在Jsp页面中提供业务逻辑功能，避免在JSP页面中直接编写java代码，造成jsp页面难以维护。

2. 自定义标签开发步骤

1、助手类　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

2、 tld

创建标签库描述文件（tld）添加自定义标签的配置，tld文件必须保存到WEB_INF目录或其子目录

3、 taglib

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

注意导包：

commons-beanutils-1.8.0.jar

commons-logging.jar

一、助手类

com.huangyucan.jsp.SetTag

package com.huangyucan.jsp;

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

public class SetTag extends BodyTagSupport{

    private static final long serialVersionUID = 6412356344625170505L;
    

    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 {
        pageContext.setAttribute(var, value);
        return SKIP_BODY;
    }
    
    
}

com.huangyucan.jsp.OutTag

package com.huangyucan.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 = 1502984121374458742L;

    private String value;

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }
    
    @Override
    public int doStartTag() throws JspException {
        JspWriter out=pageContext.getOut();
        try {
            out.print(value);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return SKIP_BODY;
    }
}

com.huangyucan.jsp.IFTag

package com.huangyucan.jsp;

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

public class IFTag extends BodyTagSupport {

    private static final long serialVersionUID = 622073552521997125L;

        
    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;
    }
    
}

com.huangyucan.jsp.ForeachTag

package com.huangyucan.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 Admin
 *
 */


public class ForeachTag extends BodyTagSupport {

    private static final long serialVersionUID = -9078639899233104183L;

    private String var;
    private List<Object> items=new ArrayList<Object>();
    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，那么指针需要循坏向下移动，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 {
//        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;
    }
    
}

com.huangyucan.jsp.SelectTag

package com.huangyucan.jsp;

import java.io.IOException;
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;

/**
 * <select id='' name=''>
         <option value='-1' selected>===请选择===</option>
         </select>
         
         <z:select...></z: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、存入数据库中的值testkey、展示列testVal
         3、加入属性(默认的头部属性值headTextKey、默认的展示列值headTextVal)
         4、加入属性，能够实现数据回显的功能selectedVal
 * @author Admin
 *
 */
public class SelectTag extends BodyTagSupport{

    private static final long serialVersionUID = 3905214201820858296L;

    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(toHTML());
        } catch (IOException | NoSuchFieldException | SecurityException | IllegalArgumentException | IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
            e.printStackTrace();
        }
        return super.doStartTag();
    }
    /**
     * 拼接出下拉列表所对应的select的html代码
     * <select id='' name=''>
         <option value='-1' selected>===请选择===</option>
         </select>
     * @return
     * @throws SecurityException 
     * @throws NoSuchFieldException 
     * @throws IllegalAccessException 
     * @throws IllegalArgumentException 
     * @throws NoSuchMethodException 
     * @throws InvocationTargetException 
     */
    private String toHTML() throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException, InvocationTargetException, NoSuchMethodException {
        StringBuilder sb=new StringBuilder();
        sb.append("<select id='"+id+"' name='"+name+"'>");
        
        if(headTextKey==null||"".equals(headTextKey)||HeadTextVal==null||"".equals(HeadTextVal)) {
            sb.append("<option value='"+headTextKey+"' selected>"+HeadTextVal+"</option> ");
        }
        String val;
        String html;
        for (Object obj : items) {
//            要让学生id存入数据，让学生的名字展示在jsp页面
//            <option value='s001'>zs</opyion>
//            obj     sid    sname
            Field textKeyField= obj.getClass ().getDeclaredField(textKey);
            textKeyField.setAccessible(true);
            val=(String) textKeyField.get(obj);
            html=BeanUtils.getProperty(obj, textVal);
            if(val.equals(selectedVal)) {
                sb.append("<option value='"+val+"' selected>"+html    +"</opyion>");
            }
            else {
                sb.append("<option value='"+val+"' >"+html    +"</opyion>");
            }
        }
        
        sb.append("</select>");
        return sb.toString();
    } 
    
}

二、tld

set、out、if、foreach、select标签的定义

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

jsp实现类

<%@page import="com.huangyucan.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="/huang" prefix="my" %>
<!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>Insert title here</title>
</head> 
<body>
        
        <my:set var="name" value="jhkhk"></my:set>
        <my:out value="${name }"></my:out> <br>
        -------------------------------
        <br><my:if test="true">hh</my:if>
        <my:if test="false">jk</my:if><br>
        -------------------------------
        <%
        List list=new ArrayList();
        list.add(new Student("s001","旺财"));
        list.add(new Student("s002","肥波"));
        list.add(new Student("s003","小明"));
        request.setAttribute("stus", list);
        %>
        <br><my:foreach items="${stus }" var="stu">
        ${stu.sid },${stu.sname }<br>
        
        </my:foreach>
        --------------------------------
        <br><my:select textVal="sname" items="${stus }" textKey="sid"></my:select>
        
        
</body>
</html>