Unit05： WEB项目的开发模式 、转发 和 Unit09： EL、JSTL

Unit05： WEB项目的开发模式 、转发   和  Unit09： EL、JSTL

dao

package dao;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import entity.Emp;

public class EmpDao implements Serializable {

    public List<Emp> findAll() {
        List<Emp> list = new ArrayList<Emp>();
        
        Emp e1 = new Emp();
        e1.setEmpno(1);
        e1.setEname("唐僧");
        e1.setJob("师父");
        e1.setSal(9000.0);
        list.add(e1);
        
        Emp e2 = new Emp();
        e2.setEmpno(2);
        e2.setEname("悟空");
        e2.setJob("徒弟");
        e2.setSal(5000.0);
        list.add(e2);
        
        Emp e3 = new Emp();
        e3.setEmpno(3);
        e3.setEname("八戒");
        e3.setJob("徒弟");
        e3.setSal(6000.0);
        list.add(e3);
        
        return list;
    }

    public void save(Emp e) {
        System.out.println(
            "增加员工:" + e.getEname());
    }
    
}
EmpDao.java

entity

package entity;

import java.io.Serializable;

public class Course implements Serializable {

    //对象的属性
    private Integer courseId;
    private String name;
    private Integer days;
    
    //Bean的属性
    //1.通过get/set方法所观察出来的属性
    //2.将get/set去掉后得到的单词首字母小写
    public Integer getId() {
        return courseId;
    }
    public void setId(Integer courseId) {
        this.courseId = courseId;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getDays() {
        return days;
    }
    public void setDays(Integer days) {
        this.days = days;
    }
    
}
Course.java
package entity;

import java.io.Serializable;

public class Emp implements Serializable {

    private Integer empno;
    private String ename;
    private String job;
    private Double sal;
    
    public Integer getEmpno() {
        return empno;
    }
    public void setEmpno(Integer empno) {
        this.empno = empno;
    }
    public String getEname() {
        return ename;
    }
    public void setEname(String ename) {
        this.ename = ename;
    }
    public String getJob() {
        return job;
    }
    public void setJob(String job) {
        this.job = job;
    }
    public Double getSal() {
        return sal;
    }
    public void setSal(Double sal) {
        this.sal = sal;
    }
    
}
Emp.java
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;
    }
    
}
Student.java

Model 1模式

　　WEB组件：Servlet/JSP

　　使用一个组件处理请求，处理业务，返回响应信息，耦合度过高，不利于代码维护

<%@page pageEncoding="utf-8"
 import="dao.*,entity.*,java.util.*"%>
<!doctype html>
<html>
    <head>
        <meta charset="utf-8"/>
        <title>查询员工</title>
        <style>
            table {
                border: 1px solid red;
                border-collapse: collapse;
                width: 30%;
            }
            td {
                border: 1px solid red;
            }
        </style>
    </head>
    <body>
        <table>
            <tr>
                <td>编号</td>
                <td>姓名</td>
                <td>职位</td>
                <td>薪资</td>
            </tr>
            <%
                EmpDao dao = new EmpDao();
                List<Emp> list = dao.findAll();
                if(list != null) {
                    for(Emp e : list) {
            %>
                    <tr>
                        <td><%=e.getEmpno() %></td>
                        <td><%=e.getEname() %></td>
                        <td><%=e.getJob() %></td>
                        <td><%=e.getSal() %></td>
                    </tr>
            <%            
                    }
                }
            %>
        </table>
    </body>
</html>
find_emp.jsp

 

Model 2模式

　　Model2引用了MVC模式对代码解耦。(重要)

　　MVC模式是经典的设计模式，是代码的分层思想：

　　　　1.M：model，即业务层，用来处理业务；

　　　　2.V：View，即视图层，用来显示数据；

　　　　3.C：controller，即控制层，负责调度，是M和V的桥梁，其作用是对代码解耦，便于团队开发及维护；

<?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>jsp2</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>findEmp</servlet-name>
      <servlet-class>web.FindEmpServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>findEmp</servlet-name>
      <url-pattern>/findEmp</url-pattern>
  </servlet-mapping>
  
  <servlet>
      <servlet-name>findStudent</servlet-name>
      <servlet-class>web.FindStudentServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>findStudent</servlet-name>
      <url-pattern>/findStudent</url-pattern>
  </servlet-mapping>
  
</web-app>
web.xml
package web;

import java.io.IOException;
import java.util.List;

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

import dao.EmpDao;
import entity.Emp;

public class FindEmpServlet extends HttpServlet {

    @Override
    protected void service(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        //查询所有员工
        EmpDao dao = new EmpDao();
        List<Emp> list = dao.findAll();
        //转发到JSP
        //1)将数据绑定到request上
        req.setAttribute("emps", list);
        //2)将请求转发给JSP
        //当前:/jsp2/findEmp
        //目标:/jsp2/emps.jsp
        req.getRequestDispatcher("emps.jsp")
            .forward(req, res);
    }

}
FindEmpServlet.java
<%@page pageEncoding="utf-8"
 import="entity.*,java.util.*"%>
<!doctype html>
<html>
    <head>
        <meta charset="utf-8"/>
        <title>查询员工</title>
        <style>
            table {
                border: 1px solid red;
                border-collapse: collapse;
                width: 30%;
            }
            td {
                border: 1px solid red;
            }
        </style>
    </head>
    <body>
        <table>
            <tr>
                <td>编号</td>
                <td>姓名</td>
                <td>职位</td>
                <td>薪资</td>
            </tr>
            <%
                List<Emp> list = (List<Emp>) 
                    request.getAttribute("emps");
                if(list != null) {
                    for(Emp e : list) {
            %>
                    <tr>
                        <td><%=e.getEmpno() %></td>
                        <td><%=e.getEname() %></td>
                        <td><%=e.getJob() %></td>
                        <td><%=e.getSal() %></td>
                    </tr>
            <%            
                    }
                }
            %>
        </table>
    </body>
</html>
emps.jsp

转发和重定向的对比(*)

1.它们的相同点

  • 　　它们都是用来解决2个WEB组件之间的跳转问题

2.它们的区别(*)

  • 　　依赖用转发
  • 　　不依赖用重定向

3.建议

  • 一般查询时用转发
  • 一般增加、修改、删除后，要重定向到查询

 　　　　Unit09： EL、JSTL　　　　

3.JSTL导包

  • 使用maven搜索jstl
  • 结果中选择1.2[jar]

4.JSTL原理

　　

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 FindStudentServlet extends HttpServlet {

    @Override
    protected void service(
        HttpServletRequest req, 
        HttpServletResponse res) throws ServletException, IOException {
        //模拟查询一个学生
        Student stu = new Student();
        stu.setName("zhangsan");
        stu.setAge(23);
        stu.setSex("M");
        stu.setInterests(
            new String[]{"篮球","足球","排球"});
        Course c = new Course();
        c.setId(1);
        c.setName("Java");
        c.setDays(82);
        stu.setCourse(c);
        //转发
        req.setAttribute("stu", stu);
        req.getRequestDispatcher("student.jsp")
            .forward(req, res);
    }

}
FindStudentServlet.java
<%@page pageEncoding="utf-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!doctype html>
<html>
    <head>
        <meta charset="utf-8"/>
        <title>查询学生</title>
    </head>
    <body>
        <!-- 2.JSTL标签 -->
        <!-- 2.1 if标签 -->
        <p>
            <c:if test="${stu.sex=='M' }">男</c:if>
            <c:if test="${stu.sex=='F' }">女</c:if>
        </p>
        <!-- 2.2 choose标签 -->
        <p>
            <c:choose>
                <c:when test="${stu.sex=='M' }">男</c:when>
                <c:otherwise>女</c:otherwise>
            </c:choose>
        </p>
        <!-- 2.3 forEach标签 -->
        <p>
            <c:forEach items="${stu.interests }" var="i">
                ${i }
            </c:forEach>
        </p>
        
        <!-- 1.EL表达式 -->
        <!-- 1.1访问Bean属性 -->
        <!-- request.getAttribute("stu").getName() -->
        <p>姓名:${stu.name }</p>
        <p>年龄:${stu.age }</p>
        <!-- 等价于stu.sex -->
        <p>性别:${stu["sex"] }</p>
        <!-- request.getAttribute("stu")
                .getCourse().getId() -->
        <p>课程ID:${stu.course.id }</p>
        <!-- 
            EL表达式的取值范围:
            1)EL默认从4个隐含对象中依次取值
              page->request->session->application
            2)默认依次取值的规则,其意义在于简化EL
               表达式,在取值时可以不用写对象名.
            3)若希望打破默认规则,明确从某对象中取值,
               则需要在表达式前面增加对象名.
              requestScope.stu.name
              sessionScope.stu.name
         -->
        <p>兴趣:${requestScope.stu.interests }</p>
        <!-- 1.2访问时可以直接运算 -->
        <p>年龄+5:${stu.age+5 }</p>
        <p>介于20-30间:${stu.age>20 && stu.age<30 }</p>
        <p>是否为空:${empty stu.interests }</p>
        <!-- 1.3直接获取请求参数 -->
        <p>参数:${param.user }</p>
    </body>
</html>
student.jsp
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原文地址：https://www.cnblogs.com/tangshengwei/p/6431532.html