引言

通过上一篇博客JavaWeb学习之三层架构实例（二）我们基本上已经实现了对学生信息列表的增删改查操作（UI除外），但是不难看出，代码冗余度太高了，尤其是StudentDao这个类，其中的增删改查四个方法，同样都要连接数据库、获取statement等等。为此，我又对这个项目进行了有点点优化。

优化日志

1、增加了两个接口 IStudentDao.java 、 IStudentService.java ；

2、 StudentDao.java 和 StudentService.java 分别实现以上两个接口，并加入Impl后缀；

3、 增加一个数据库帮助类 DBUtil.java，目的是简化Dao层代码量；

代码

代码结构

数据库帮助类DBUtil.java

这是一个通用的类，任何的数据库操作（增删改查），都可以通过这各类来实现（不仅仅是对student表的增删改查）；



	package com.ajy.util;

	import java.sql.*;

	//通用的数据库操作方法

	public class DBUtil {

	    private static String URL="jdbc:mysql://localhost:3306/anjiyubase?&serverTimezone=UTC&useSSL=false&allowPublicKeyRetrieval=false";

	    private static String DRIVER="com.mysql.cj.jdbc.Driver";

	    private static String NAME="root";

	    private static String PWD="121181";

	    public static Connection con = null;

	    public static PreparedStatement pstmt = null;

	    public static ResultSet rs = null;

	    /***

	     *增删改查四个功能，分两大块

	     *  第一块：增删改

	     *  第二块：查询

	     */

	    //实现增删改功能

	    public static boolean executeUpdate(String sql,Object[] objects){

	        try {

	            createPreparedStatement(sql,objects).executeUpdate();

	            shutDownDB(null,pstmt,con);

	            return true;

	        } catch (SQLException | ClassNotFoundException e) {

	            e.printStackTrace();

	            return false;

	        }

	    }

	    //实现查询功能

	    public static ResultSet executeQuery(String sql,Object[] objects){

	        try {

	            rs = createPreparedStatement(sql,objects).executeQuery();

	            return rs;

	        } catch (SQLException | ClassNotFoundException e) {

	            e.printStackTrace();

	            return null;

	        }

	    }

	    public static void shutDownDB(ResultSet rs,Statement stmt,Connection con) throws SQLException {

	        if (rs!=null)rs.close();

	        if (stmt!=null)stmt.close();

	        if (con!=null)con.close();

	    }

	    public static Connection getConnection() throws SQLException, ClassNotFoundException {

	        Class.forName(DRIVER);

	        return DriverManager.getConnection(URL,NAME,PWD);

	    }

	    public static PreparedStatement createPreparedStatement(String sql,Object[] objects) throws SQLException, ClassNotFoundException {

	        pstmt = getConnection().prepareStatement(sql);

	        if (objects != null) {

	            for (int i = 0; i < objects.length; i++) {

	                pstmt.setObject(i + 1, objects[i]);

	            }

	        }

	        return pstmt;

	    }

	}

学生类Student.java



package com.ajy.entity;

public class Student {

    private int stuNo;

    private String stuName;

    private int stuAge;

    private String stuAddress;

    public Student(int stuNo,String stuName,int stuAge,String stuAddress){

        this.stuNo = stuNo;

        this.stuName = stuName;

        this.stuAge = stuAge;

        this.stuAddress = stuAddress;

    }

    public Student(String stuName,int stuAge,String stuAddress){

        this.stuNo = stuNo;

        this.stuName = stuName;

        this.stuAge = stuAge;

        this.stuAddress = stuAddress;

    }

    public int getStuNo() {

        return stuNo;

    }

    public void setStuNo(int stuNo) {

        this.stuNo = stuNo;

    }

    public String getStuName() {

        return stuName;

    }

    public void setStuName(String stuName) {

        this.stuName = stuName;

    }

    public int getStuAge() {

        return stuAge;

    }

    public void setStuAge(int stuAge) {

        this.stuAge = stuAge;

    }

    public String getStuAddress() {

        return stuAddress;

    }

    public void setStuAddress(String stuAddress) {

        this.stuAddress = stuAddress;

    }

    @Override

    public String toString() {

        return getStuNo()+"--"+getStuName()+"--"+getStuAge()+"--"+getStuAddress();

    }

}

数据访问层

接口IStudentDao.java



package com.ajy.dao;

import com.ajy.entity.Student;

import java.util.List;

public interface IStudentDao {

    public boolean addStudent(Student stu);

    //查询学生是否存在

    public boolean isExits(int stuNo);

    //查询学生

    public Student queryStudent(int stuNo);

    //查询全部学生

    public List<Student> queryAll();

    //根据学号删除学生

    public boolean deleteStudentBySno(int Sno);

    //根据学号修改学号对应的学生信息

    public boolean updateStudentBySno(int sno,Student stu);

}

实现类StudentDaoImpl.java



package com.ajy.dao.impl;

import com.ajy.dao.IStudentDao;

import com.ajy.entity.Student;

import com.ajy.util.DBUtil;

import java.sql.*;

import java.util.ArrayList;

import java.util.List;

public class StudentDaoImpl implements IStudentDao {

    //增加学生信息

    public boolean addStudent(Student stu){

        String sql = "insert into student values(?,?,?,?)";

        Object[] objects = {stu.getStuNo(),stu.getStuName(),stu.getStuAge(),stu.getStuAddress()};

        return DBUtil.executeUpdate(sql,objects);

    }

    //查询学生是否存在

    public boolean isExits(int stuNo){

        return queryStudent(stuNo)==null?false:true;

    }

    //查询学生

    public Student queryStudent(int stuNo){

        String sql = "select *from student where sno=?";

        Object[] objects = {stuNo};

        ResultSet rs = DBUtil.executeQuery(sql,objects);

        try {

            if (rs.next()){

                int sno = rs.getInt("sno");

                String sname = rs.getString("sname");

                int sage = rs.getInt("sage");

                String saddress= rs.getString("saddress");

                return new Student(sno,sname,sage,saddress);

            }else{

                return null;

            }

        } catch (SQLException e) {

            e.printStackTrace();

            return null;

        }

    }

    //查询全部学生

    public List<Student> queryAll(){

        String sql = "select*from student";

        ResultSet rs = DBUtil.executeQuery(sql,null);

        try{

            List<Student> list = new ArrayList<>();

            while (rs.next()){

                int sno = rs.getInt("sno");

                String sname = rs.getString("sname");

                int sage = rs.getInt("sage");

                String saddress= rs.getString("saddress");

                list.add(new Student(sno,sname,sage,saddress));

            }

            return list;

        } catch (SQLException e) {

            e.printStackTrace();

            return null;

        }finally {

            try {

                DBUtil.shutDownDB(DBUtil.rs,DBUtil.pstmt,DBUtil.con);

            } catch (SQLException e) {

                e.printStackTrace();

                return null;

            }

        }

    }

    //根据学号删除学生

    public boolean deleteStudentBySno(int Sno){

        String sql = "delete from student where sno=?";

        Object[] objects = {Sno};

        return DBUtil.executeUpdate(sql,objects);

    }

    //根据学号修改学号对应的学生信息

    public boolean updateStudentBySno(int sno,Student stu){

        String sql = "update student set sname=?,sage=?,saddress=? where sno=?";

        Object[] objects = {stu.getStuName(),stu.getStuAge(),stu.getStuAddress(),sno};

        return DBUtil.executeUpdate(sql,objects);

    }

}

业务逻辑层

接口IStudentService.java



package com.ajy.service;

import com.ajy.entity.Student;

import java.util.List;

public interface IStudentService {

    //增加学生

    public boolean addStudent(Student stu);

    //根据学号删除学生

    public boolean deleteStudentBySno(int sno);

    //根据学号查询学生

    public Student queryStudentBySno(int sno);

    //根据学号，更新对应的学生

    public boolean updateStudentBySno(int sno,Student stu);

    //查询全部学生

    public List<Student> queryStudentAll();

}

实现类StudentServiceImpl.java



package com.ajy.service.impl;

import com.ajy.dao.IStudentDao;

import com.ajy.dao.impl.StudentDaoImpl;

import com.ajy.entity.Student;

import com.ajy.service.IStudentService;

import java.util.List;

public class StudentServiceImpl implements IStudentService {

    IStudentDao studentDao = new StudentDaoImpl();

    //增加学生

    public boolean addStudent(Student stu){

        if (!studentDao.isExits(stu.getStuNo())){

            return studentDao.addStudent(stu);

        }else{

            return false;

        }

    }

    //根据学号删除学生

    public boolean deleteStudentBySno(int sno){

        //先判断学生是否存在

        if(!studentDao.isExits(sno)){

            return false;

        }else{

            return studentDao.deleteStudentBySno(sno);

        }

    }

    //根据学号查询学生

    public Student queryStudentBySno(int sno){

        return studentDao.queryStudent(sno);

    }

    //根据学号，更新对应的学生

    public boolean updateStudentBySno(int sno,Student stu){

        //先判断此学号对应的学生是否存在

        if(!studentDao.isExits(sno)){

            return false;

        }else{

            return studentDao.updateStudentBySno(sno,stu);

        }

    }

    //查询全部学生

    public List<Student> queryStudentAll(){

        return studentDao.queryAll();

    }

}

视图层

后端代码

AddStudentServlet.java



package com.ajy.servlet;

import com.ajy.entity.Student;

import com.ajy.service.IStudentService;

import com.ajy.service.impl.StudentServiceImpl;

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;

@WebServlet(name = "AddStudentServlet",value = "/AddStudentServlet")

public class AddStudentServlet 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 {

        request.setCharacterEncoding("utf-8");

        int stuNo = Integer.parseInt(request.getParameter("stuNo"));

        String stuName = request.getParameter("stuName");

        int stuAge = Integer.parseInt(request.getParameter("stuAge"));

        String stuAddress = request.getParameter("stuAddress");

        Student stu = new Student(stuNo,stuName,stuAge,stuAddress);

        IStudentService addStudentService = new StudentServiceImpl();

        boolean res = addStudentService.addStudent(stu);

        if (res){

            request.setAttribute("res","添加成功");

        }else{

            request.setAttribute("res","添加失败");

        }

        request.getRequestDispatcher("QueryAllStudents").forward(request,response);

    }

}

DeleteStudentServlet.java



package com.ajy.servlet;

import com.ajy.service.IStudentService;

import com.ajy.service.impl.StudentServiceImpl;

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.io.PrintWriter;

@WebServlet(name = "DeleteStudentServlet",value = "/DeleteStudentServlet")

public class DeleteStudentServlet 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 {

        request.setCharacterEncoding("utf-8");

        //根据学号删除学生

        int sno = Integer.parseInt(request.getParameter("sno"));

        IStudentService studentService = new StudentServiceImpl();

        boolean res = studentService.deleteStudentBySno(sno);

        if (res){

            request.setAttribute("res","删除成功");

        }else{

            request.setAttribute("res","删除失败");

        }

        request.getRequestDispatcher("QueryAllStudents").forward(request,response);

    }

}

QueryAllStudents.java



package com.ajy.servlet;

import com.ajy.entity.Student;

import com.ajy.service.IStudentService;

import com.ajy.service.impl.StudentServiceImpl;

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;

@WebServlet(name = "QueryAllStudents",value = "/QueryAllStudents")

public class QueryAllStudents 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 {

        request.setCharacterEncoding("utf-8");

        IStudentService studentService = new StudentServiceImpl();

        List<Student> studentList = studentService.queryStudentAll();

        request.setAttribute("students",studentList);

        request.getRequestDispatcher("studentlist.jsp").forward(request,response);

    }

}

QueryStudentBySno.java



package com.ajy.servlet;

import com.ajy.entity.Student;

import com.ajy.service.IStudentService;

import com.ajy.service.impl.StudentServiceImpl;

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;

@WebServlet(name = "QueryStudentBySno",value = "/QueryStudentBySno")

public class QueryStudentBySno 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 {

        request.setCharacterEncoding("utf-8");

        IStudentService studentService = new StudentServiceImpl();

        int sno = Integer.parseInt(request.getParameter("sno"));

        Student stu = studentService.queryStudentBySno(sno);

        request.setAttribute("student",stu);

        request.getRequestDispatcher("updateinfo.jsp").forward(request,response);

    }

}

UpdateStudentBySnoServlet.java



package com.ajy.servlet;

import com.ajy.entity.Student;

import com.ajy.service.IStudentService;

import com.ajy.service.impl.StudentServiceImpl;

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;

@WebServlet(name = "UpdateStudentBySnoServlet",value = "/UpdateStudentBySnoServlet")

public class UpdateStudentBySnoServlet 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 {

        request.setCharacterEncoding("utf-8");

        IStudentService studentService = new StudentServiceImpl();

        int sno = Integer.parseInt(request.getParameter("sno"));

        String sname = request.getParameter("sname");

        int sage = Integer.parseInt(request.getParameter("sage"));

        String saddress = request.getParameter("saddress");

        Student student = new Student(sname,sage,saddress);

        boolean res = studentService.updateStudentBySno(sno,student);

        if (res){

            request.setAttribute("res","修改成功");

        }else{

            request.setAttribute("res","修改失败");

        }

        request.getRequestDispatcher("QueryAllStudents").forward(request,response);

    }

}
前端代码

前端代码没有改动,这里就不贴了.

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