EL

最新推荐文章于 2024-05-31 16:12:14 发布

Ward_Tian

最新推荐文章于 2024-05-31 16:12:14 发布

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分类专栏： java基础

本文链接：https://blog.youkuaiyun.com/Ward_Tian/article/details/83834705

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本文详细介绍了Java Web应用程序的构建过程，包括实体类设计、Servlet处理逻辑及EL表达式的使用。通过创建Student和Course实体类，演示了如何在Servlet中设置属性，并在JSP页面上使用EL表达式来显示数据，同时展示了EL表达式的多种用法。

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package entity;

import java.io.Serializable;

public class Course implements Serializable {
   private Integer courseId;
   private String courseName;
   private Integer days;

   //对象属性：courseId
   //Bean属性：id
   public Integer getId() {
       return courseId;
   }
   public void setId(Integer courseId) {
       this.courseId = courseId;
   }
   public String getCourseName() {
       return courseName;
   }
   public void setCourseName(String courseName) {
       this.courseName = courseName;
   }
   public Integer getDays() {
       return days;
   }
   public void setDays(Integer days) {
       this.days = days;
   }

}

------------------------------------------------Student---------------------------------------------------------

package entity;

import java.io.Serializable;

public class Student implements Serializable {
           private String name;
           private Integer age;
           private String sex;
           private String[] interests;
           private Course course;


           public String getName() {
               return name;
           }
           public void setName(String name) {
               this.name = name;
           }
           public Integer getAge() {
               return age;
           }
           public void setAge(Integer age) {
               this.age = age;
           }
           public String getSex() {
               return sex;
           }
           public void setSex(String sex) {
               this.sex = sex;
           }
           public String[] getInterests() {
               return interests;
           }
           public void setInterests(String[] interests) {
               this.interests = interests;
           }
           public Course getCourse() {
               return course;
           }
           public void setCourse(Course course) {
               this.course = course;
           }



}

---

---------------------------
---------------------------------------------------------------------DemoServlet-----------------

package web;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import entity.Course;
import entity.Student;

public class DemoServlet extends HttpServlet {

   @Override
   protected void service(HttpServletRequest req,
           HttpServletResponse res) throws ServletException, IOException {
           //模拟查询学生数据
       Student s=new Student();
       s.setName("tian");
       s.setAge(18);
       s.setSex("f");
       s.setInterests(new String[] {"讲课","篮球","羽毛球"});
       Course c=new Course();
       c.setId(1);
       c.setCourseName("JAVA");
       c.setDays(80);
       s.setCourse(c);

       //转发到JSP
       //当前：/Jsp3/demo
       //目标： /Jsp3/demo.jsp
       req.setAttribute("stu", s);
       req.getRequestDispatcher("demo.jsp").forward(req, res);

   }

}

------------------------------------

----------------------------------------------------web.xml-------------------------------------------

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
<display-name>Jsp3</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
 <servlet>
 <servlet-name>demo</servlet-name>
 <servlet-class>web.DemoServlet</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>demo</servlet-name>
 <url-pattern>/demo</url-pattern>
 </servlet-mapping>

</web-app>

-----------------------------------------------------------demo.jsp----------------------------------------

<%@page pageEncoding="utf-8"%>
<!doctype html>
<html>
<head>
 <meta charset="utf-8">
 <title>EL和JSTL</title>
</head>
 <body>
 <h1>EL</h1>
 
 
 姓名：${stu.name}
 年龄：${stu["age"]}
 
 课程：${stu.course.id }
 
 年龄+5=:${stu.age+5 }
 年龄是否大于20?：${stu.age>20 }
 年龄介于10-20之间？${stu.age>10&&stu.age<20 }
 判断是否为空${empty stu }
 判空:${stu==null }
 
 参数：路径/demo?x=5:${param.x}
 
 ${requestScope.stu }

 </body>
</html>