30.JSTL與EL表達(dá)式

1.初識(shí)EL表達(dá)式

image.png

1.1 簡(jiǎn)單認(rèn)識(shí)EL

//Stduent.java
package com.imooc.el;

public class Student {
    public String name;
    public String mobile;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getMobile() {
        return mobile;
    }
    public void setMobile(String mobile) {
        this.mobile = mobile;
    }
    
    
}
//StduentServlet.java
package com.imooc.el;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class StduentServlet
 */
@WebServlet("/StduentServlet")
public class StduentServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public StduentServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Student stu = new Student();
        stu.setName("hachiman");
        stu.setMobile(null);
        String grade = "A";
        request.setAttribute("student", stu);
        request.setAttribute("grade", grade);
        request.getRequestDispatcher("/el_info.jsp").forward(request, response);
        
    }

}

用普通的jsp表達(dá)式

//info.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" import="com.imooc.el.Student"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <% 
        Student stu = (Student)request.getAttribute("student");
        String grade = (String)request.getAttribute("grade");
        out.println("<h1>姓名："+stu.getName()+"</h1>");
        out.println("<h2>手機(jī)："+stu.getMobile()+"</h2>");
        out.println("<h2>教師評(píng)級(jí)："+grade+"</h2>");
    %>
</body>
</html>

注意需要導(dǎo)入類(lèi)import="com.imooc.el.Student"
用el表達(dá)式，則無(wú)需導(dǎo)入類(lèi)，而且輸出也簡(jiǎn)化很多

//el_info.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <h1>姓名:${requestScope.student.name}</h1>
    <h2>手機(jī):${requestScope.student.mobile }</h2>
    <h2>評(píng)級(jí):${requestScope.grade}</h2>
</body>
</html>

1.2EL作用域?qū)ο?/h2>
image.png
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Student stu = new Student();
        stu.setName("hachiman");
        stu.setMobile(null);
        String grade = "A";
        HttpSession session = request.getSession();
        session.setAttribute("student", stu);
        session.setAttribute("grade", grade);
        /*在不同的作用域設(shè)置同名屬性*/
        request.setAttribute("grade", "A");//request作用域
        session.setAttribute("grade", "B");//session作用域
        request.getServletContext().setAttribute("grade", "C");//context全局作用域
        
        //request.setAttribute("student", stu);
        //request.setAttribute("grade", grade);
        request.getRequestDispatcher("/el_info.jsp").forward(request, response);
        
    }
//jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <h1>姓名:${sessionScope.student.name}</h1>
    <h2>手機(jī):${sessionScope.student.mobile }</h2>
    <h2>評(píng)級(jí):${sessionScope.grade}</h2>
    
    <h1>姓名:${student.name}</h1>
    <h2>手機(jī):${student.mobile }</h2>
    <h2>評(píng)級(jí):${grade}</h2>
</body>
</html>

1.3 EL表達(dá)式輸出

image.png

image.png

zh

注意：
1.對(duì)于直接輸出類(lèi)，本質(zhì)上是執(zhí)行類(lèi)的toString方法，因此重寫(xiě)toString方法可以修改輸出內(nèi)容
2.對(duì)于EL輸出時(shí)，EL人性化將輸出為null的對(duì)象，輸出為空，在頁(yè)面上就看不到null了

1.4EL輸出參數(shù)

image.png

http://localhost:8080/ServletProj/StduentServlet?teacher=andy
可以用<h2>講師:${param.teacher}</h2>直接獲取

2.JSTL標(biāo)簽庫(kù)

2.1簡(jiǎn)介

JSTL標(biāo)簽庫(kù)

*JSTL(JSP Standard Tag Library),JSP標(biāo)準(zhǔn)標(biāo)簽庫(kù)
*JSTL用于簡(jiǎn)化JSP開(kāi)發(fā)，提高代碼的可讀性和可維護(hù)性

JSTL的標(biāo)簽庫(kù)種類(lèi)
JSTL按功能劃分為五類(lèi)標(biāo)簽庫(kù)
核心標(biāo)簽庫(kù) -core
格式化輸出標(biāo)簽庫(kù) -fmt
SQL操作標(biāo)簽庫(kù) -sql
XML操作標(biāo)簽庫(kù) -xml
函數(shù)標(biāo)簽庫(kù) -functions

引用JSTL核心庫(kù)
核心標(biāo)簽庫(kù)（Core）是JSTL最重要的標(biāo)簽庫(kù) 提供了JSTL的基礎(chǔ)功能
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
JSTL核心標(biāo)簽庫(kù)在taglib-standard-impl.jar由META-INF/c.tld定義

image.png

2.2判斷標(biāo)簽

image.png

注意：?jiǎn)畏种?lt;c:if>是沒(méi)有else的，多分支就不要寫(xiě)這個(gè)

//ServletJstl.java
package com.imooc.jstl;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ServletJstl
 */
@WebServlet("/jstl")
public class ServletJstl extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public ServletJstl() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setAttribute("score",58);
        request.setAttribute("grade", "B");
        request.getRequestDispatcher("/core.jsp").forward(request, response);
    }

}

//core.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>    

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <!-- 單分支 -->
    <h1>${requestScope.score}</h1>
    <c:if test = "${ score >= 60}">
        <h1 style = "color:green">恭喜，通過(guò)測(cè)試</h1>
    </c:if>
    <c:if test = "${requestScope.score < 60}">
        <h1 style="color:red">抱歉，請(qǐng)?jiān)俳釉賲?lt;/h1>
    </c:if>
    
    <!-- 多分支 -->
    <h1>${grade}</h1>
    <c:choose>
        <c:when test = "${grade == 'A' }">
            <h2>你很優(yōu)秀</h2>
        </c:when>
        <c:when test = "${grade == 'B' }">
            <h2>不錯(cuò)哦</h2>
        </c:when>
        <c:when test = "${grade == 'C' }">
            <h2>水平一般，需要提高</h2>
        </c:when>
        <c:when test = "${grade == 'D'}">
            <h2>需要努力啦，不要?dú)怵H</h2>
        </c:when>
        <c:otherwise>
            <h2>一切隨緣吧</h2>
        </c:otherwise>
    </c:choose>
    
</body>
</html>

2.3 遍歷標(biāo)簽

image.png
//Company.java
package com.imooc.jstl;

public class Company {
    private String cname;
    private String url;
    public Company(String cname,String url) {
        this.cname = cname;
        this.url = url;
    }
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public String getUrl() {
        return url;
    }
    public void setUrl(String url) {
        this.url = url;
    }
    
}


//ServletJstl.java
@WebServlet("/jstl")
public class ServletJstl extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public ServletJstl() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<Company> list = new ArrayList();
        list.add(new Company("騰訊","www.tencent.com"));
        list.add(new Company("百度","www.baidu.com"));
        list.add(new Company("慕課網(wǎng)","www.imooc.com"));
        request.setAttribute("companies", list);
        request.getRequestDispatcher("/core.jsp").forward(request, response);
    }

}

//core.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>    

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>

   <!-- 遍歷標(biāo)簽 --> 
    <c:forEach items="${requestScope.companies}" var="c" varStatus="idx">
        <h2>${idx.index+1}.${c.cname}-${c.url }</h2>
    </c:forEach>
    
</body>
</html>

2.4 fmt標(biāo)簽

image.png
//fmt.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
    <%
        request.setAttribute("amt", 19876543.567);
        request.setAttribute("now",new java.util.Date());
        request.setAttribute("html","<a href='index.html'>index</a>");
        request.setAttribute("nothing", null);
    %>
    <h1>${requestScope.now}</h1>
    
    <!-- formatDate pattern 
        yyyy - 四位年
        MM - 兩位月
        dd - 兩位日
        HH - 24小時(shí)制
        hh - 12小時(shí)制
        mm - 分鐘
        ss - 秒
        SSS - 毫秒
    -->
    <h1>
        <fmt:formatDate value="${requestScope.now }" pattern="yyyy年MM月dd日HH時(shí)mm分ss秒SSS毫秒"/>
    </h1>
    
    <h1>${requestScope.amt}</h1>
    <h1>
        <!-- 保留小數(shù)點(diǎn)后兩位 -->
        <fmt:formatNumber value="${requestScope.amt}" pattern="0.00"></fmt:formatNumber>
    </h1>
    <h1>
        <!-- 增加分割逗號(hào) -->
        ￥<fmt:formatNumber value="${requestScope.amt}" pattern="0,000.00"></fmt:formatNumber>元
    </h1>
    <!-- c:out 與 `uri="http://java.sun.com/jsp/jstl/core" prefix="c" `標(biāo)簽庫(kù)有關(guān) -->
    <h1>
        <!-- 修改null輸出為空的情況，該為自定義 -->
        null默認(rèn)值：<c:out value="${nothing}" default="無(wú)"></c:out>
    </h1>
    <h1>
        <!-- 輸出帶有特殊字符，選擇是否需要進(jìn)行轉(zhuǎn)譯，保證原樣輸出 -->
        <c:out value="${html}" escapeXml="true"></c:out>
    </h1>
</body>
</html>
image.png
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