Javaweb项目 利用JSP响应浏览器

Posted 2021-02-16 一只初学小菜鸟

一、javaweb  数据访问流程？

1.浏览器 http 访问服务器 找到 servlet（HttpServeltDemo.java文件） 

2.servle 通过dao 访问数据库 数据库将数据返回给servlet

3.servlet找寻指定的JSP文件 将student数据传送给JSP

4.JSP获得数据，展示在网页上。将数据返回给servlet

5.servlet将数据 传送给浏览器。

 

二、将数据库中的student 展示在http页面 。代码体现 ？

 　　装备工作建立四个包。

1.dao

package com.aaa.dao;

import com.aaa.entity.Student;

import java.util.List;
import java.util.Map;

public interface IStudentDAO {
    boolean add(Student s);

    boolean delete(int id);
    boolean update(Student s);

    Map<String ,Object> getStudent(int id);

    List<Map<String,Object>> getAllStudent();
}

dao.Impl  实现一个 供测试使用。

package com.aaa.dao.Impl;

import com.aaa.dao.IStudentDAO;
import com.aaa.entity.Student;
import com.aaa.util.DBUtil;

import java.util.List;
import java.util.Map;

public class StudentDAOImpl implements IStudentDAO {
    @Override
    public boolean add(Student s) {
        return false;
    }

    @Override
    public boolean delete(int id) {
        return false;
    }

    @Override
    public boolean update(Student s) {
        return false;
    }

    @Override
    public Map<String, Object> getStudent(int id) {
        return null;
    }

    @Override
    public List<Map<String, Object>> getAllStudent() {
        String sql="select * from student  ";
        return   DBUtil.executeQuery(sql);

    }
}

2.entity 实体类

package com.aaa.entity;

public class Student {
    private int id;
    private String name;
    private int age;

    public Student(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public Student() {
        super();
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name=‘" + name + ‘‘‘ +
                ", age=" + age +
                ‘}‘;
    }
}

3.封装工具类

package com.aaa.util;

import java.sql.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class DBUtil {
    static {
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    public  static Connection getConnetion(){
        try {
          return   DriverManager.getConnection("jdbc:mysql://localhost:3306/qy66?characterEnconding=UTF-8","root","root");
        } catch (SQLException e) {
            e.printStackTrace();
        }
       return null;
    }
    public  static boolean executeUpdate(String sql,Object... args){
        Connection con=null;
        PreparedStatement ps=null;

        try {
            con=DBUtil.getConnetion();
            ps=con.prepareStatement(sql);

            for (int i = 0; i <args.length ; i++) {
                ps.setObject(i+1,args[i]);
            }
            int i=ps.executeUpdate();
            return  i>0;

        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            close(con,ps,null);
        }
        return  false;
    }

    public static List<Map<String, Object>>  executeQuery(String sql, Object... args){
        Connection con=null;
        PreparedStatement ps=null;
        ResultSet rs=null;


        try {
            con=getConnetion();
            ps=con.prepareStatement(sql);

            for (int i = 0; i <args.length ; i++) {
                ps.setObject(i+1,args[i]);
            }
           rs=ps.executeQuery();

            List<Map<String,Object>>list=new ArrayList<>();

            int count=rs.getMetaData().getColumnCount();

            while (rs.next()){

                Map<String,Object>map= new HashMap<>();

                for (int i = 0; i < count; i++) {
                    String name = rs.getMetaData().getColumnLabel(i + 1);
                    map.put(name,rs.getObject(name));
                }
                list.add(map);
            }
            return list;

        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            close(con,ps,rs);
        }
        return null;
    }

    private static void close(Connection con, PreparedStatement ps, ResultSet rs) {
        if (rs!=null){
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (ps!=null){
            try {
                ps.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (con!=null){
            try {
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

}

4.servlet 测试。

package com.aaa.servlet;

import com.aaa.dao.IStudentDAO;
import com.aaa.dao.Impl.StudentDAOImpl;

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.List;
import java.util.Map;
@WebServlet("/666") //虚拟路径 不用再配置xml文件  快捷
public class HttpServletDemo extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.获取数据库中的数据
        IStudentDAO dao=new StudentDAOImpl();
        List<Map<String, Object>> list = dao.getAllStudent();
        
       /*
            2.请求共享数据 就是需要servlet展示什么数据 
            req.setattribute("01",list)  展示list数据 名字叫01【关键字的作用】 因为这种文件可能
            会有很多  方便servlet找的到  我们所需要的JSP文件
         */
        req.setAttribute("01",list);
        
        //3.请求转发到某个JSP  3.1 新建JSP文件 day01.jsp
        req.getRequestDispatcher("day01.jsp").forward(req,resp);
    }
}

5.JSP 代码部分？

<%@ page import="java.util.List" %>
<%@ page import="java.util.Map" %><%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2019/4/15
  Time: 22:57
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<html>
<head>
    <title>Title</title>
</head>
<body>
    <table border="1" cellspacing="0">
        <tr>
            <th>id</th>
            <th>name</th>
            <th>age</th>
        </tr>
                <!--1. 在JSP中获取数据-->
                <!--6.a:注意JSP写在 web目录下  b:lib目录建立在 WEB-INF下-->
        <% List<Map<String,Object>>list=(List<Map<String,Object>>)request.getAttribute("01");%> <!-- 2.强制装换-->

        <%     for (Map map:list) {      %>  <!--3. java 代码在JSP中书写方式  for循环  获得每一列中的数据     -->
        <tr>
            <td> <%=map.get("id")%> </td>   <!-- 5.‘=‘等于号 是将java代码显示在 网页上-->
            <td> <%=map.get("name")%>> </td>
            <td> <%=map.get("age")%>> </td>
        </tr>


        <%  }  %> <!--4. for循环的结尾-->
    </table>
</body>
</html>