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  • JavaEE EL & JSTL 学习笔记

    1. EL表达式(特别重要)

     

    1.1 EL简介

      不是一种语言,只是一个表达式而已,是JSP中专门用于显示数据用的,SinceJSP2.0

    主要作用:获取数据并显示到页面上。

    简单易用:

    <%
    List<Book> cart = (List<Book>)request.getSession.getAttribute(“cart”);
    out.write(cart.get(0).getName());
    %>
    

      EL:${cart[0].name}  简单,写起来方便。

      实际开发:不要在JSP中使用Java表达式,而要使用EL表达式。

    1.2 EL表达式的基本语法

    ${EL表达式}

    EL表达式,是从四大域对象中取数据的。

    EL表达式中没有空指针异常,也没有数组越界,没有字符串连接。

    1.3 EL获取数据

    1.3.1 获取对象的属性

    例子用到的类:

    package com.itheima.domain;
    
    import java.io.Serializable;
    
    public class Student implements Serializable {
    	private String name = "牛骞";
    	private String gender;
    	private int age;
    	private Address address = new Address();
    	
    	public Student(){}
    	
    	public Student(String name, String gender, int age) {
    		super();
    		this.name = name;
    		this.gender = gender;
    		this.age = age;
    	}
    	public String getName() {
    		return name;
    	}
    	public void setName(String name) {
    		this.name = name;
    	}
    	public String getGender() {
    		return gender;
    	}
    	public void setGender(String gender) {
    		this.gender = gender;
    	}
    	public int getAge() {
    		return age;
    	}
    	public void setAge(int age) {
    		this.age = age;
    	}
    
    	public Address getAddress() {
    		return address;
    	}
    
    	public void setAddress(Address address) {
    		this.address = address;
    	}
    	
    }
    
    package com.itheima.domain;
    
    public class Address {
    	private String province = "山东省";
    	private String city = "济南市";
    	public String getProvince() {
    		return province;
    	}
    	public void setProvince(String province) {
    		this.province = province;
    	}
    	public String getCity() {
    		return city;
    	}
    	public void setCity(String city) {
    		this.city = city;
    	}
    	
    }
    
    <%@page import="com.itheima.domain.Student"%>
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>EL获取数据</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
          <br/>-------EL是从四个域范围中查找数据的(不要忘记)---------<br/>
        <%
        Student s1 = new Student();
        request.setAttribute("s", s1);
        %>
        ${s}
        <%--模拟原理
        Student s = (Student)pageContext.findAttribute("s");
        out.write(s);
        --%>
        <br/>-------EL获取JavaBean的属性---------<br/>
        ${s.name}=${s["name"]}=${s['name']}
        <br/>-------EL获取JavaBean的关联对象的属性---------<br/>
        ${s.address.province}=${s.address.city}
        <hr/>
        <br/>-------EL获取数组中的元素---------<br/>
        <%
        String strs[] = {"陈冠希","钟欣桐","张白痴","谢霆锋"};
        pageContext.setAttribute("strs", strs);
        %>
        ${strs[1]}${strs[100]}
        <br/>-------EL获取List的元素---------<br/>
        <%
        List<String> list = new ArrayList<String>();
        list.add("aaa");
        list.add("bbb");
        list.add("ccc");
        pageContext.setAttribute("list", list);
         %>
        ${list[1]}
        <br/>-------EL获取Map的数据:Map.Entry   getKey  getValue---------<br/>
        <%
        Map map = new HashMap();//根据key获取value
        map.put("a", "aaaa");
        map.put("b", "bbbb");
        map.put("c", "cccc");
        pageContext.setAttribute("map", map);
        %>
        ${map.b}
        <%--
        map.getKey("b");
        --%>
      </body>
    </html>

    1.3.2 EL运算符

    算数、逻辑、关系

     

    l  empty运算符:

    判断一个字符串是否为””或其他对象是否为null,同时还能判断集合中是否有元素。

    l  三元运算符:

    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>EL运算</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
          <br/>------empty运算符--------<br/>
          <%
          pageContext.setAttribute("s1", "");
          pageContext.setAttribute("s2", null);
          List list = new ArrayList();
          list.add("aa");
          pageContext.setAttribute("list", list);
          String strs[] = {};
          pageContext.setAttribute("strs", strs);
           %>
        ${empty s1}<br/>
        ${empty s2}<br/>
        ${empty list}<br/>
        ${empty strs}<br/>
        <br/>------三元运算符--------<br/>
        <%
        pageContext.setAttribute("gender", "female");
         %>
         <input type="radio" name="gender" value="male" ${gender=='male'?'checked="checked"':''}/><input type="radio" name="gender" value="female" ${gender=='female'?'checked="checked"':''}/></body>
    </html>

    1.3.3 EL中的隐含对象

    PS:(难点:不要和JSP的隐含对象混淆)

    这小节的视频是更换过的。

    <%JSP隐含对象%>

    ${EL隐含对象}

    EL隐含对象名称

    类型

    JSP隐含对象名称

    备注

    pageContext

    javax.servlet.jsp.PageContext

    pageContext

    这个完全一样

    pageScope

    java.util.Map

    没有

    页面范围中的数据

    requestScope

    java.util.Map

    没有

    请求范围中的数据

    sessionScope

    java.util.Map

    没有

    会话范围中的数据

    applicationScope

    java.util.Map

    没有

    应用范围中的数据

    Param

    java.util.Map

    没有

    请求参数。key:请求参数名,value:请求参数值

    paramValues

    java.util.Map

    没有

    请求参数。key:请求参数名,value:请求参数值数组

    Header

    java.util.Map

    没有

    请求消息头。key:消息头名称,value:消息头值String

    headerValues

    java.util.Map

    没有

    请求消息头。key:消息头名称,value:消息头值数组

    initParam

    java.util.Map

    没有

    全局参数配置。

    Cookie

    java.util.Map

    没有

    key:是Cookie对象的name,value是Cookie对象本身

    <%@page import="com.it.domain.Person"%>
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>EL的隐含对象</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
          <%--=pageContext --%><br/>
          ${pageContext}<br/>
          当前应用名称:${pageContext.request.contextPath}<br/>
          ${pageContext.response.characterEncoding}<br/>
          HttpSession的ID:<%=session.getId() %><br/>
          HttpSession的ID:${pageContext.session.id}<br/>
          <br/>
          <%
          pageContext.setAttribute("p", "pp");
        request.setAttribute("p", "rp");
        session.setAttribute("p", "sp");
        application.setAttribute("p", "ap");
          %>
          ${p}<br/><!-- pageContext.findAttribute("p") -->
          ${pageScope.p }<br/><!-- pageContext.findAttribute("p",page_Scope) -->
          ${requestScope.p }<br/>
          ${sessionScope.p }<br/>
          ${applicationScope.p }<br/>
          <%
              //pageContext.setAttribute("user", "haha");
              session.setAttribute("user", new Person());
          %>
          ${user.name }<br/>
          ${sessionScope.user.name }<br/>
          <hr/>
          获取消息头的值:ACcept-Encoding<br/>
          JSP:<%=request.getHeader("ACcept-Encoding") %><br/>
          EL: ${header['ACcept-Encoding']} <br/> <!-- 不能使用点号  --> 
          ${headerValues['ACcept-Encoding'][0] }<br/>
          <!-- http://localhost/day11_00_el/3el.jsp?name=abc&password=456&password=123 -->
          ${param.name}:${param.password}<br/>
          ${paramValues.name[0]}:${paramValues.password[0]}:${paramValues.password[1]}<br/>
          ${cookie.JSESSIONID.value }<br/>
          ${initParam.wuj}
      </body>
    </html>

    1.3.4 定义和使用EL函数

    EL不支持字符串操作

    a、定义EL函数的开发步骤

    1、定义一个普通类,提供实现功能的静态方法(EL函数只能调用静态方法)

    package com.itheima.jsp;
    
    public class MyFunctions {
    	public static String toUppercase(String s){
    		return s.toUpperCase();
    	}
    }
    

    2、EL函数进行配置:在WEB-INF目录下建立一个扩展名为tld(Tag Libary Definition)的xml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">
        <tlib-version>1.0</tlib-version>
        <short-name>myfn</short-name>
        <uri>http://www.itheima.com/jsp/functions</uri>
        <function>
            <name>toUppercase</name>
            <function-class>com.itheima.jsp.MyFunctions</function-class>
            <function-signature>java.lang.String toUppercase( java.lang.String )</function-signature>
        </function>
    </taglib>

    3、在JSP中使用自定义的EL函数

    首先:通过taglib指令引入外部的函数库

    <%@ taglib uri="http://www.itheima.com/jsp/functions" prefix="myfn"%>

    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://www.itheima.com/jsp/functions" prefix="myfn"%>
    <%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn"%>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>使用EL函数</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
          <%
          pageContext.setAttribute("s", "abcdefg");
           %>
           ${myfn:toUppercase(s)}
           <hr/>
           ${fn:contains("Tomcat","cat")}
           <hr/>
           ${fn:split("2008-09-08","-")[0] }<br/>
           ${fn:split("2008-09-08","-")[1] }<br/>
           ${fn:split("2008-09-08","-")[2] }<br/>
           <hr/>
           <%
           pageContext.setAttribute("data", "<h1>黑马真好</h1>");
            %>
            ${fn:escapeXml(data)}
      </body>
    </html>

    2. 自定义标签:简单标签

    2.1 标签的作用

    控制JSP中的逻辑处理。替换掉JSP中的Java脚本。

    2.2 标签的编写步骤

    javax.servlet.jsp.tagext.SimpleTag中的方法:

      void doTag():遇到自定义标签时由服务器调用执行。

      JspTag getParent():得到父标签的引用。

      void setJspBody(JspFragment jsp):由服务器调用,传出JSP的片段

      void setJspContext(JspContext jc):由服务器调用,传入当前页面的PageContext

      void setParent(JspTag parent):由服务器调用,传入他的父标签

     

    a、编写一个类,实现javax.servlet.jsp.tagext.SimpleTag,或者继承javax.servlet.jsp.tagext.SimpleTagSupport

    package com.itheima.tag;
    
    import java.io.IOException;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.PageContext;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class ShowRemoteIpSimpleTag extends SimpleTagSupport {
    	public ShowRemoteIpSimpleTag(){
    		System.out.println("实例化了");
    	}
    	public void doTag() throws JspException, IOException {
    		PageContext pc = (PageContext)getJspContext();
    		String ip = pc.getRequest().getRemoteAddr();
    	    pc.getOut().write(ip);
    	}
    	
    }
    

    b、对标签处理类进行配置

    在WEB-INF目录下建立一个扩展名为tld的xml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">
        <tlib-version>1.0</tlib-version>
        <short-name>itheima</short-name>
        <uri>http://www.itheima.com/jsp/tags</uri>
        <tag>
            <name>showRemoteIp</name>
            <tag-class>com.itheima.tag.ShowRemoteIpSimpleTag</tag-class>
            <!-- 说明标签的主体内容 :没有就写empty-->
            <body-content>empty</body-content>
        </tag> 
    </taglib>

    c、在JSP中使用

    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://www.itheima.com/jsp/tags" prefix="itheima"%>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>输出来访者的IP地址</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
          您的IP是:
        <%--
        String ip = request.getRemoteAddr();
        out.write(ip);
         --%>
         <itheima:showRemoteIp/>
      </body>
    </html>
    
    

    2.3 标签具体的作用:4个方面

    a、控制主体内容是否显示。

    package com.itheima.tag;
    
    import java.io.IOException;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.JspWriter;
    import javax.servlet.jsp.PageContext;
    import javax.servlet.jsp.tagext.JspFragment;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class Demo1SimpleTag extends SimpleTagSupport {
    	//主体内容不需要显示,就什么都不写
    //	public void doTag() throws JspException, IOException {
    //	}
    	//让主体内容显示:得到主体内容,用字符流输出即可
    	public void doTag() throws JspException, IOException {
    //		JspFragment jf = getJspBody();//代表标签的主体内容
    //		PageContext pc = (PageContext)getJspContext();
    //		JspWriter out = pc.getOut();
    //		jf.invoke(out);
    		
    		getJspBody().invoke(null);
    	}
    }
    
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://www.itheima.com/jsp/tags" prefix="itheima"%>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>控制主体内容是否显示</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
          我喜欢
         <itheima:demo1>good</itheima:demo1>
      </body>
    </html>

    b、控制结束标签后的JSP内容不执行。

    package com.itheima.tag;
    
    import java.io.IOException;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.JspWriter;
    import javax.servlet.jsp.PageContext;
    import javax.servlet.jsp.SkipPageException;
    import javax.servlet.jsp.tagext.JspFragment;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class Demo2SimpleTag extends SimpleTagSupport {
    	public void doTag() throws JspException, IOException {
    		throw new SkipPageException();
    	}
    }
    
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://www.itheima.com/jsp/tags" prefix="itheima"%>
    
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>控制结束标签后的JSP内容不执行</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body><itheima:demo2/>喜欢男人
      </body>
    </html>

    c、控制主体内容重复执行

    package com.itheima.tag;
    
    import java.io.IOException;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.JspWriter;
    import javax.servlet.jsp.PageContext;
    import javax.servlet.jsp.SkipPageException;
    import javax.servlet.jsp.tagext.JspFragment;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class Demo3SimpleTag extends SimpleTagSupport {
    	
    	private int count;//自动转换
    	
    	
    	public void setCount(int count) {
    		this.count = count;
    	}
    
    
    	public void doTag() throws JspException, IOException {
    		for(int i=0;i<count;i++){
    			getJspBody().invoke(null);
    		}
    	}
    }
    
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://www.itheima.com/jsp/tags" prefix="itheima"%>
    
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>控制主体内容重复执行</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
      
          <% int i = 3; %>
          <itheima:demo3 count="${1+4}">
              girl<br/>
          </itheima:demo3>
      </body>
    </html>

    d、改变主体内容后再输出

    package com.itheima.tag;
    
    import java.io.IOException;
    import java.io.StringWriter;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.JspWriter;
    import javax.servlet.jsp.PageContext;
    import javax.servlet.jsp.SkipPageException;
    import javax.servlet.jsp.tagext.JspFragment;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class Demo4SimpleTag extends SimpleTagSupport {
    	
    	public void doTag() throws JspException, IOException {
    		StringWriter sw = new StringWriter();
    		//得到主体内容
    		JspFragment jf =getJspBody();
    		jf.invoke(sw);
    		//变为大写后输出
    		String content = sw.toString();
    		content = content.toUpperCase();
    		
    		PageContext pc = (PageContext)getJspContext();
    		pc.getOut().write(content);
    	}
    }
    
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://www.itheima.com/jsp/tags" prefix="itheima"%>
    
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>改变主体内容后再输出</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
      
          <itheima:demo4>
              abcdefg${1+1}
          </itheima:demo4>
      </body>
    </html>

    4个 demo tld 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">
        <tlib-version>1.0</tlib-version>
        <short-name>itheima</short-name>
        <uri>http://www.itheima.com/jsp/tags</uri>
        <tag>
            <name>demo1</name>
            <tag-class>com.itheima.tag.Demo1SimpleTag</tag-class>
            <!-- 说明标签的主体内容 :有就写scriptless.简单标签时使用-->
            <body-content>scriptless</body-content>
        </tag>
        <tag>
            <name>demo2</name>
            <tag-class>com.itheima.tag.Demo2SimpleTag</tag-class>
            <body-content>empty</body-content>
        </tag>
        <tag>
            <name>demo3</name>
            <tag-class>com.itheima.tag.Demo3SimpleTag</tag-class>
            <body-content>scriptless</body-content>
            <attribute>
                <name>count</name>
                <required>true</required>
                <!-- rt:RunTime expr:Expression value  是否支持表达式:java表达式或EL表达式-->
                <rtexprvalue>true</rtexprvalue>
            </attribute>
        </tag>
        <tag>
            <name>demo4</name>
            <tag-class>com.itheima.tag.Demo4SimpleTag</tag-class>
            <body-content>scriptless</body-content>
        </tag>
    </taglib>

    2.4 标签的详细配置

    <body-content>取值:

    JSP:jsp中能出现啥,标签主体内容就能出现啥。给传统标签用的。简单标签一用就报错。

    empty:没有主体内容。简单和传统标签都能用。

    scriptless:给简单标签用的,说明主体内容是非脚本。

    tagdependent:把主体内容的EL表达式当做普通字符串对待。

     

    2.5 自定义标签案例:4个

    1.实现if

    package com.itheima.examples;
    
    import java.io.IOException;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class IfSimpleTag extends SimpleTagSupport {
    	private boolean test;
    
    	public void setTest(boolean test) {
    		this.test = test;
    	}
    
    	public void doTag() throws JspException, IOException {
    		if(test){
    			getJspBody().invoke(null);
    		}
    	}
    	
    }
     
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://www.itheima.com/jsp/examples" prefix="h"%>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>实现if语句的功能</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
        <%
        List list = new ArrayList();
        list.add("abc");
        pageContext.setAttribute("cart", list);
        %>
        <h:if test="${empty cart}">
            对不起!您没有购买任何商品
        </h:if>
        <h:if test="${!empty cart}">
            您购买的商品如下
        </h:if>
      </body>
    </html>

     2.实现if else语句的功能

    package com.itheima.examples;
    
    import java.io.IOException;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class ChooseSimpleTag extends SimpleTagSupport {
    	private boolean flag;
    	
    	public boolean isFlag() {
    		return flag;
    	}
    
    	public void setFlag(boolean flag) {
    		this.flag = flag;
    	}
    
    	public void doTag() throws JspException, IOException {
    		getJspBody().invoke(null);
    	}
    	
    }
    
    package com.itheima.examples;
    
    import java.io.IOException;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class WhenSimpleTag extends SimpleTagSupport {
    	private boolean test;
    	
    
    	public void setTest(boolean test) {
    		this.test = test;
    	}
    
    
    	public void doTag() throws JspException, IOException {
    		if(test){
    			getJspBody().invoke(null);
    			//把父标签的标记改一下
    			ChooseSimpleTag p = (ChooseSimpleTag)getParent();
    			p.setFlag(true);
    		}
    	}
    	
    }
    
    package com.itheima.examples;
    
    import java.io.IOException;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class OtherwiseSimpleTag extends SimpleTagSupport {
    
    	public void doTag() throws JspException, IOException {
    		ChooseSimpleTag p = (ChooseSimpleTag)getParent();
    		if(!p.isFlag()){
    			getJspBody().invoke(null);
    		}
    	}
    	
    }
    
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://www.itheima.com/jsp/examples" prefix="h"%>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>实现if else语句的功能</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
        <%
        pageContext.setAttribute("grade", "A");
        %>
        <h:choose>
               <h:when test="${grade=='A'}">
                   优秀
               </h:when>
               <h:otherwise>
                   尚需努力
               </h:otherwise>
           </h:choose>
      </body>
    </html>

    3.实现forEach语句的功能

    package com.itheima.examples;
    
    import java.io.IOException;
    import java.util.List;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.PageContext;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class ForEach1SimpleTag extends SimpleTagSupport {
    	private List items;
    	private String var;//类型写String
    	public void setItems(List items) {
    		this.items = items;
    	}
    	public void setVar(String var) {
    		this.var = var;
    	}
    	public void doTag() throws JspException, IOException {
    		PageContext pc = (PageContext)getJspContext();
    		for(Object obj:items){
    			pc.setAttribute(var, obj);
    			getJspBody().invoke(null);
    		}
    	}
    	
    }
    
    package com.itheima.examples;
    
    import java.io.IOException;
    import java.lang.reflect.Array;
    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.Collection;
    import java.util.List;
    import java.util.Map;
    import java.util.Set;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.PageContext;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class ForEach2SimpleTag extends SimpleTagSupport {
    	private Object items;
    	private String var;//类型写String
    	
    	private Collection collection = new ArrayList();
    	
    	public void setItems(Object items) {
    		//向collection中放数据
    		if(items instanceof List){
    			collection = (List)items;
    		}else if(items instanceof Set){
    			collection = (Set)items;
    		}else if(items instanceof Map){
    			collection = ((Map)items).entrySet();
    //		}else if(items instanceof Object[]){
    //			collection = Arrays.asList((Object[])items);
    //		}else if(items instanceof int[]){
    //			int[] ii = (int[])items;
    //			for(int i:ii){
    //				collection.add(i);
    //			}
    //		}
    //		
    		//反射数组:Class.isArray()只要是数组,返回true
    		}else if(items.getClass().isArray()){
    			//是一个数组
    			int len = Array.getLength(items);// items数组的长度
    			for(int i=0;i<len;i++){
    				collection.add(Array.get(items, i));
    			}
    		}else{
    			throw new RuntimeException("不支持的类型");
    		}
    	}
    	public void setVar(String var) {
    		this.var = var;
    	}
    	public void doTag() throws JspException, IOException {
    		PageContext pc = (PageContext)getJspContext();
    		for(Object obj:collection){
    			pc.setAttribute(var, obj);
    			getJspBody().invoke(null);
    		}
    	}
    	
    }
    
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://www.itheima.com/jsp/examples" prefix="h"%>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>实现forEach语句的功能</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
        <%
        List list = new ArrayList();
        list.add("aaa");
        list.add("bbb");
        list.add("ccc");
        pageContext.setAttribute("list", list);
        %>
           <h:forEach1 items="${list}" var="l">
               ${l}<br/>
           </h:forEach1>
      </body>
    </html>
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://www.itheima.com/jsp/examples" prefix="h"%>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>实现forEach语句的功能</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
        <%
        List list = new ArrayList();
        list.add("aaa");
        list.add("bbb");
        list.add("ccc");
        pageContext.setAttribute("list", list);
        %>
           <h:forEach2 items="${list}" var="l">
               ${l}<br/>
           </h:forEach2>
           <hr/>
           <%
           Set set = new HashSet();
           set.add("aa");
           set.add("bb");
           set.add("cc");
           pageContext.setAttribute("set", set);
            %>
            <h:forEach2 items="${set}" var="l">
               ${l}<br/>
           </h:forEach2>
           <hr/>
           <%
           Map map = new HashMap();
           map.put("a", "aaaa");
           map.put("b", "bbbb");
           map.put("c", "cccc");
           pageContext.setAttribute("map", map);
            %>
            <h:forEach2 items="${map}" var="me">
               ${me.key}=${me.value}<br/>
           </h:forEach2>
           <hr/>
           <%
       String strs[] = {"aaaaa","bbbbb","ccccc"};
           pageContext.setAttribute("strs", strs);
            %>
            <h:forEach2 items="${strs}" var="s">
               ${s}<br/>
           </h:forEach2>
           <hr/>
           <%
       int ii[] = {1,2,3,4,5};
           pageContext.setAttribute("ii", ii);
            %>
            <h:forEach2 items="${ii}" var="s">
               ${s}<br/>
           </h:forEach2>
      </body>
    </html>

    4.html标记过滤的标签

    package com.itheima.examples;
    
    import java.io.IOException;
    import java.io.StringWriter;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.PageContext;
    import javax.servlet.jsp.tagext.SimpleTagSupport;
    
    public class HtmlFilterSimpleTag extends SimpleTagSupport {
    	public void doTag() throws JspException, IOException {
    		StringWriter sw = new StringWriter();//带有缓存功能的字符输出流
    		getJspBody().invoke(sw);
    		String content = sw.toString();//<h1>你好</h1>
    		content = filter(content);// <h1>你好</h1>
    		PageContext pc = (PageContext)getJspContext();
    		pc.getOut().write(content);
    	}
    
    	private String filter(String message) {
    		if (message == null)
                return (null);
    
            char content[] = new char[message.length()];
            message.getChars(0, message.length(), content, 0);
            StringBuffer result = new StringBuffer(content.length + 50);
            for (int i = 0; i < content.length; i++) {
                switch (content[i]) {
                case '<':
                    result.append("<");
                    break;
                case '>':
                    result.append(">");
                    break;
                case '&':
                    result.append("&");
                    break;
                case '"':
                    result.append(""");
                    break;
                default:
                    result.append(content[i]);
                }
            }
            return (result.toString());
    	}
    	
    }
    
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://www.itheima.com/jsp/examples" prefix="h"%>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>html标记过滤的标签</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
        <h:htmlFilter>
            <h1>你好</h1>
        </h:htmlFilter>
      </body>
    </html>

    以上自定义 EL 函数的 配置 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">
        <tlib-version>1.0</tlib-version>
        <short-name>h</short-name>
        <uri>http://www.itheima.com/jsp/examples</uri>
        
        <tag>
            <name>if</name>
            <tag-class>com.itheima.examples.IfSimpleTag</tag-class>
            <body-content>scriptless</body-content>
            <attribute>
                <name>test</name>
                <required>true</required>
                <rtexprvalue>true</rtexprvalue>
            </attribute>
        </tag>
        <tag>
            <name>choose</name>
            <tag-class>com.itheima.examples.ChooseSimpleTag</tag-class>
            <body-content>scriptless</body-content>
        </tag>
        <tag>
            <name>when</name>
            <tag-class>com.itheima.examples.WhenSimpleTag</tag-class>
            <body-content>scriptless</body-content>
            <attribute>
                <name>test</name>
                <required>true</required>
                <rtexprvalue>true</rtexprvalue>
            </attribute>
        </tag>
        <tag>
            <name>otherwise</name>
            <tag-class>com.itheima.examples.OtherwiseSimpleTag</tag-class>
            <body-content>scriptless</body-content>
        </tag>
        <tag>
            <name>forEach1</name>
            <tag-class>com.itheima.examples.ForEach1SimpleTag</tag-class>
            <body-content>scriptless</body-content>
            <attribute>
                <name>items</name>
                <required>true</required>
                <rtexprvalue>true</rtexprvalue>
            </attribute>
            <attribute>
                <name>var</name>
                <required>true</required>
                <rtexprvalue>false</rtexprvalue>
            </attribute>
        </tag>
        <tag>
            <name>forEach2</name>
            <tag-class>com.itheima.examples.ForEach2SimpleTag</tag-class>
            <body-content>scriptless</body-content>
            <attribute>
                <name>items</name>
                <required>true</required>
                <rtexprvalue>true</rtexprvalue>
            </attribute>
            <attribute>
                <name>var</name>
                <required>true</required>
                <rtexprvalue>false</rtexprvalue>
            </attribute>
        </tag>
        <tag>
            <name>htmlFilter</name>
            <tag-class>com.itheima.examples.HtmlFilterSimpleTag</tag-class>
            <body-content>scriptless</body-content>
        </tag>
    </taglib>

    3. JSTL标签库

    3.1 JSTL简介

      JSP Standard Tag Libary:JSP中标准的标签库。

      Apache实现的。

      导入jar包:JavaEE的jar包中包含。

    3.2 JSTL的组成

      Core:核心标签库。通用逻辑处理

      Fmt:国际化有关。

      Functions:EL函数

      SQL:操作数据库。不用

      XML:操作XML。不用

    3.3 JSTL中Core

    例子中用到的类: Person

    package com.itheima.domain;
    
    import java.io.Serializable;
    
    public class Person implements Serializable {
    	private String name;
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    	
    }
    
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>开发中不常用</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
          <br/>-------c:out输出内容到页面上-------------<br/>
          <%
          pageContext.setAttribute("d1", "<h1>abcdefg</h1>");
           %>
        <c:out value="${d1}" default="木有" escapeXml="true"></c:out><br/>
        ${d1}<br/>
        <br/>-------c:set不经常用。能把某个值存到指定的域范围中设置JavaBean的属性、设置Map的key和value-------------<br/>
        <c:set var="p" value="ppp" scope="request"></c:set>
        ${requestScope.p}<br/>
        <jsp:useBean id="person" class="com.itheima.domain.Person" scope="page"></jsp:useBean>
        Name:${person.name}<br/>
        <c:set value="牛骞" property="name" target="${person}"></c:set>
        Name:${person.name}<br/>
        <%
        pageContext.setAttribute("map", new HashMap());
         %>
         <c:set value="aaa" property="a" target="${map}"></c:set>
         ${map.a}
         <br/>----------c:remove 从指定范围删除属性,没有指定范围,则四个范围全删----------<br/>
         <%
         pageContext.setAttribute("s", "ps");
         request.setAttribute("s", "rs");
         session.setAttribute("s", "ss");
         application.setAttribute("s", "as");
          %>
          <c:remove var="s"/>
          page:${pageScope.s}<br/>
          request:${requestScope.s}<br/>
          session:${sessionScope.s}<br/>
          application:${applicationScope.s}<br/>
      </body>
    </html>
    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
    <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <title>title</title>
        
        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <!--
        <link rel="stylesheet" type="text/css" href="styles.css">
        -->
    
      </head>
      
      <body>
          <br/>----------如同catch代码块-----------<br/>
          <c:catch var="e">
            <jsp:useBean id="p1" class="com.itheima.domain.Person"></jsp:useBean>
            ${p1.gender}
        </c:catch>
        <hr/>
        ${e.message}
      </body>
    </html>

    foreach:

    <body>
        <%
        pageContext.setAttribute("strs", new String[]{"a","b"});
        %>
        <c:forEach items="${strs}" var="s">
            ${s}<br/>
        </c:forEach>
        <hr/>
        <%
        List list = new ArrayList();
        list.add("aa");
        list.add("bb");
        pageContext.setAttribute("list", list);
        %>
        <c:forEach items="${list}" var="s">
            ${s}<br/>
        </c:forEach>
        <hr/>
        <%
        Map map = new HashMap();
        map.put("a", "aaa");
        map.put("b", "bbb");
        pageContext.setAttribute("map", map);
        %>
        <c:forEach items="${map}" var="me">
            ${me.key}=${me.value}<br/>
        </c:forEach>
        <hr/>
        <c:forEach begin="1" end="100" var="num">
            ${num}
        </c:forEach>
        <hr/>
        <%
        pageContext.setAttribute("strs1", new String[]{"a","b","c","d","e","f","g"});
        %>
        <c:forEach items="${strs1}" begin="1" end="5" step="2" var="s">
            ${s}<br/>
        </c:forEach>
        <hr/>
        <br/>-------开发中------<br/>
        <%
        List students = new ArrayList();
        students.add(new Student("牛骞","female",19));
        students.add(new Student("织万","male",29));
        students.add(new Student("薛振宇","male",39));
        students.add(new Student("刘飞","female",39));
        pageContext.setAttribute("stus", students);
        %>
        <table border="1" width="438">
            <tr>
                <th>序号</th>
                <th>姓名</th>
                <th>性别</th>
                <th>年龄</th>
            </tr>
            <!-- 
            varStatus:取值为一个字符串,就是一个变量名,引用一个对象
                该对象记录着当前遍历的元素的信息。
                int getIndex():当前元素的索引。
                int getCount():当前元素计数。
                boolean isFirst():是否第一个
                boolean isLast():
            
             -->
            <c:forEach items="${stus}" var="s" varStatus="vs">
                <tr class="${vs.index%2==0?'odd':'even'}">
                    <td>${vs.count}</td>
                    <td>${s.name}</td>
                    <td>${s.gender=='male'?'男':'女'}</td>
                    <td>${s.age}</td>
                </tr>
            </c:forEach>
        </table>
      </body>

    import:

    <br/>--------包含:多了能包含任何页面的功能-----------<br/>
        <c:import url="/forEach.jsp"></c:import>
        <hr/>
        <c:import url="http://www.baidu.com"></c:import>

    url:

    <br/>-------url构建一个地址:URL重写;地址服务器用的,value的/就表示当前应用-----------<br/>
          <br/>-------url和param一同使用,可以对中文参数进行URL编码-----------<br/>
        <c:url value="/url.jsp"></c:url><br/>
        <c:url value="/forEach.jsp" var="forEachUrl1"></c:url>
        <a href="${forEachUrl1}">猛戳1</a><br/>
        <c:url value="/forEach.jsp" var="forEachUrl2">
            <c:param name="username" value="王昭珽"></c:param>
            <c:param name="password" value="123"></c:param>
        </c:url>
        <a href="${forEachUrl2}">猛戳2</a><br/>

    3.4 JSTL中的Functions

    taglib指令导入:

    l  fn:contains函数:用于判断在源字符串中是否包含目标字符串。

    l  fn:containsIgnoreCase函数:用于判断在源字符串中是否包含目标字符串,并且在判断时忽略大小写。

    l  fn:startsWith函数:用于判断源字符串是否以指定的目标字符串开头。

    l  fn: endsWith函数:用于判断源字符串是否以指定的目标字符串结尾。

    l  fn:indexOf函数:用于在源字符串中查找目标字符串,并返回源字符串中最先与目标字符串匹配的第一个字符的索引。

    l  fn:replace函数:用于把源字符串中的一部分替换为另外的字符串,并返回替换后的字符串。

    l  fn:substring函数:用于获取源字符串中的特定子字符串。

    l  fn:substringBefore函数:用于获取源字符串中指定子字符串之前的子字符串。

    l  fn: substringAfter函数:用于获取源字符串中指定子字符串之后的子字符串

    l  fn:split函数:用于将源字符串拆分为一个字符串数组。

    l  fn:join函数:用于将源字符串数组中的所有字符串连接为一个字符串。

    l  fn:toLowerCase函数:用于将源字符串中的所有字符改为小写。

    l  fn: toUpperCase函数:用于将源字符串中的所有字符改为大写。

    l  fn:trim函数:用于将源字符串中的开头和末尾的空格删除。

    l  fn:escapeXml函数:用于将源字符串中的字符“<”、“>”、“””和“&”等转换为转义字符。

    l  fn:length函数:用于返回字符串中的字符的个数,或者集合和数组的元素的个数

    总结

    一、EL表达式
    作用:替换掉JSP中的Java表达式。
    1、基本语法:
    ${p}    从四个域范围中查找数据
    2、获取数据:
        JavaBean的属性、List中的元素、Map中的数据(根据key找value)
    3、运算:逻辑、关系、empty、三元运算。
        empty:如果一个集合不是null,其中没有元素,也是空的。
    4、EL的隐含对象
        pageContext
        pageScope
        requestScope
        sessionScope
        applicationScope
        
        param
        paramValues
        header
        headerValues
        initParam
        cookie:  Map,key:是cookie的name;value:cookie对象
    5、自定义EL函数
        a、定义一个普通类,类的方法必须是静态的
        b、建立tld文件,定义函数
        c、在JSP中通过taglib指令导入,使用
    二、自定义简单标签
    1、标签的作用:替换JSP中的Java脚本
    2、编码步骤
    3、四个具体作用
    4、自定义几个标签,发行自己的标签库
    三、JSTL
        Core Functions Format SQL XML
    1、Functions:字符串操作有关。
    2、JSTL中的核心标签

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  • 原文地址:https://www.cnblogs.com/loveincode/p/EL_JSTL.html
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