JSTL表达式的用法（IDEA)

JSTL（Java Server Page Standard Tag Library) JSP标准标签库，用来替代JSP页面脚本，它与EL（Expression Language）配合可以有效地减少JSP页面中的Java代码。

1.通用基本标签（set,out,remove)

<%--var：变量名,value:变量值--%>
<c:set var="count" value="99" />
<c:out value="${count}"/><hr>
<%--如果变量未被定义值，可声明默认值--%>
<c:out value="${happy}" default="我是默认值"/><hr>
<%--移除值--%>
<c:remove var="count"/>
<c:out value="${count}"/><hr>

输出结果：

2.条件标签

<c:if test="${8>4}">
    <h3>你好 2020</h3>
</c:if>

<c:set var="score" value="70"/>
<c:choose>
    <c:when test="${score>=90 }">优秀</c:when>
    <c:when test="${score>=80 }">良好</c:when>
    <c:when test="${score>=70 }">中等</c:when>
    <c:when test="${score>=60 }">及格</c:when>
    <c:otherwise>不及格</c:otherwise>
</c:choose>

其中要注意两点

无<c:else>标签
choose,when组合即Java中Swith语句的效果

3.循环foreach的使用：

一.简单循环：

<c:forEach var="i" begin="0" end="10" step="2">
    ${i}<br>
</c:forEach><hr>

二.集合的遍历：

新建TestServlet.java:

package com.qianqian.practice.servlet;

import com.qianqian.practice.entity.User;

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

@WebServlet(name = "TestServlet", value = "/test")
public class TestServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<User> userList=new ArrayList<>();
        userList.add(new User("4567654","李华","7545","man"));
        userList.add(new User("5452545","张梁","8775","woman"));
        userList.add(new User("6456455","康康","2421","woman"));
        userList.add(new User("1312313","小明","5457","man"));
        request.setAttribute("userList",userList);
        request.getRequestDispatcher("/index.jsp").forward(request, response);
    }
}

index.jsp:

<body>

<table border="1" width="30%" bordercolor="black" cellspacing="0" align="center">
    <tr>
        <th>ID</th>
        <th>NAME</th>
        <th>PASSWORD</th>
        <th>GENDER</th>
    </tr>

    <c:forEach items="${userList}" var="user">
        <tr>
            <td>${user.userId}</td>
            <td>${user.userName}</td>
            <td>${user.userPassword}</td>
            <td>${user.userGender}</td>
        </tr>
    </c:forEach>
</table>
</body>

结果：

关于EL用法，详见博文：https://blog.csdn.net/qq_42013035/article/details/104079926

秋.凝

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JSTL表达式的用法（IDEA)

1.通用基本标签（set,out,remove)

2.条件标签

3.循环foreach的使用：

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