引言

这个实例是上一个实例JavaWeb学习 三层架构实例（一）的加强版，实现的是在前端对数据库中student表的 增、删、改、查 操作。关于三层组成云云，这里就不再叙述。

实例

效果图

先来看一下主页，将student表中的数据列出来，这里隐藏了地址信息（saddress）。

这是添加学生信息的页面

这是修改学生信息的页面（学号不可修改）

由于删除学生信息不需要跳转，所以没有删除学生信息的页面。这几个功能的操作结果都会在主页的左上角显示。

项目结构

如图,自上到下,

StudentDao.java 是直接对数据库进行增删改查操作的,属于原子性的操作,没有逻辑性,只是简单的增删改查.比如,它并不会在删除某条信息之前先判断这条信息是否存在.

Student.java 是"学生"类,此类拥有诸如学号、姓名、年龄、地址等信息以及对应的getter和setter方法。

StudentService.java 这个类，名子含义有点模糊，属于service层，同样是对数据库进行增删改查操作，与上面的Dao类不同的是，service层的操作具有逻辑性，就拿添加学生信息来说，service会先调用Dao类的查询方法，先判断这个学生是否存在，根据结果进行信息插入操作。

Servlet包 易发现,这个包中存放的都是Servlet类,属于视图层的后端,每一个类每一个类对应一个视图层前端的功能(增删改查);

代码

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();        }    }

StudentDao.java

package com.ajy.dao;        import com.ajy.entity.Student;        import java.sql.*;    import java.util.ArrayList;    import java.util.List;        public class StudentDao {        private final String URL="jdbc:mysql://localhost:3306/anjiyubase?&serverTimezone=UTC&useSSL=false&allowPublicKeyRetrieval=true";        private final String DRIVER="com.mysql.cj.jdbc.Driver";        private final String NAME="root";        private final String PWD="121181";            //增加学生信息        public boolean addStudent(Student stu){            Connection con = null;            PreparedStatement pstmt = null;            int count = 0;            try {                Class.forName(DRIVER);                con = DriverManager.getConnection(URL,NAME,PWD);                String sql = "insert into student values(?,?,?,?)";                pstmt = con.prepareStatement(sql);                pstmt.setInt(1,stu.getStuNo());                pstmt.setString(2,stu.getStuName());                pstmt.setInt(3,stu.getStuAge());                pstmt.setString(4,stu.getStuAddress());                count = pstmt.executeUpdate();            } catch (ClassNotFoundException e) {                e.printStackTrace();                return false;            } catch (SQLException e) {                e.printStackTrace();                return false;            }finally {                try {                    if (pstmt!=null)pstmt.close();                    if (con!=null)con.close();                } catch (SQLException e) {                    e.printStackTrace();                    return false;                }            }            if(count==0){                return false;            }else{                return true;            }        }            //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){            Connection con = null;            PreparedStatement pstmt = null;            ResultSet rs = null;            Student stu = null;            int count = 0;            try {                Class.forName(DRIVER);                con = DriverManager.getConnection(URL,NAME,PWD);                String sql = "select * from student where sno=?";                pstmt = con.prepareStatement(sql);                pstmt.setInt(1,stuNo);                rs = pstmt.executeQuery();                if (rs.next()){                    stu = new Student(rs.getInt("sno"),                            rs.getString("sname"),                            rs.getInt("sage"),                            rs.getString("saddress"));                }            } catch (ClassNotFoundException e) {                e.printStackTrace();                return null;            } catch (SQLException e) {                e.printStackTrace();                return null;            }finally {                try {                    if (rs!=null)rs.close();                    if (pstmt!=null)pstmt.close();                    if (con!=null)con.close();                } catch (SQLException e) {                    e.printStackTrace();                    return null;                }            }            return stu;        }            //查询全部学生        public List
    
      queryAll(){            Connection con = null;            Statement stmt = null;            ResultSet rs = null;            List
     
       list = new ArrayList<>();            try {                Class.forName(DRIVER);                con = DriverManager.getConnection(URL,NAME,PWD);                String sql = "select *from student";                stmt = con.createStatement();                rs = stmt.executeQuery(sql);                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));                }            } catch (ClassNotFoundException e) {                e.printStackTrace();                return null;            } catch (SQLException e) {                e.printStackTrace();                return null;            }finally {                try {                    if (rs!=null)rs.close();                    if (stmt!=null)stmt.close();                    if (con!=null)con.close();                    return list;                } catch (SQLException e) {                    e.printStackTrace();                    return null;                }            }        }            //根据学号删除学生        public boolean deleteStudentBySno(int Sno){            Connection con = null;            PreparedStatement pstmt = null;            int count = 0;            try {                Class.forName(DRIVER);                con = DriverManager.getConnection(URL,NAME,PWD);                String sql = "delete from student where sno=?";                pstmt = con.prepareStatement(sql);                pstmt.setInt(1,Sno);                count = pstmt.executeUpdate();            } catch (ClassNotFoundException e) {                e.printStackTrace();                return false;            } catch (SQLException e) {                e.printStackTrace();                return false;            }finally {                try {                    if (pstmt!=null)pstmt.close();                    if (con!=null)con.close();                } catch (SQLException e) {                    e.printStackTrace();                    return false;                }            }            if(count==0){                return false;            }else{                return true;            }        }            //根据学号修改学号对应的学生信息        public boolean updateStudentBySno(int sno,Student stu){            Connection con = null;            PreparedStatement pstmt = null;            int count = 0;            try {                Class.forName(DRIVER);                con = DriverManager.getConnection(URL,NAME,PWD);                String sql = "update student set sname=?,sage=?,saddress=? where sno=?";                pstmt = con.prepareStatement(sql);                //要修改的人                pstmt.setInt(4,sno);                //修改该后的内容                pstmt.setString(1,stu.getStuName());                pstmt.setInt(2,stu.getStuAge());                pstmt.setString(3,stu.getStuAddress());                count = pstmt.executeUpdate();            } catch (ClassNotFoundException e) {                e.printStackTrace();                return false;            } catch (SQLException e) {                e.printStackTrace();                return false;            }finally {                try {                    if (pstmt!=null)pstmt.close();                    if (con!=null)con.close();                } catch (SQLException e) {                    e.printStackTrace();                    return false;                }            }            if(count==0){                return false;            }else{                return true;            }        }    }
     
    

StudentService

package com.ajy.service;        import com.ajy.dao.StudentDao;    import com.ajy.entity.Student;        import java.util.List;        public class StudentService {        StudentDao studentDao = new StudentDao();            //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
    
      queryStudentAll(){            return studentDao.queryAll();        }    }
    

QueryAllStudents.java

package com.ajy.servlet;        import com.ajy.entity.Student;    import com.ajy.service.StudentService;        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;    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");            StudentService studentService = new StudentService();            List
    
      studentList = studentService.queryStudentAll();                request.setAttribute("students",studentList);                request.getRequestDispatcher("studentlist.jsp").forward(request,response);        }    }
    

AddStudentServlet.java

package com.ajy.servlet;        import com.ajy.entity.Student;    import com.ajy.service.StudentService;        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);            StudentService addStudentService = new StudentService();            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.StudentService;    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"));            StudentService studentService = new StudentService();            boolean res = studentService.deleteStudentBySno(sno);                response.setContentType("text/html;charset=utf-8");            response.setCharacterEncoding("utf-8");                PrintWriter out = response.getWriter();            if (res){                request.setAttribute("res","删除成功");            }else{                request.setAttribute("res","删除失败");            }            request.getRequestDispatcher("QueryAllStudents").forward(request,response);        }    }

UpdateStudentBySnoServlet.java

package com.ajy.servlet;        import com.ajy.entity.Student;    import com.ajy.service.StudentService;    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");            StudentService studentService = new StudentService();                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);        }    }

QueryStudentBySno.java

package com.ajy.servlet;        import com.ajy.entity.Student;    import com.ajy.service.StudentService;    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");            StudentService studentService = new StudentService();            int sno = Integer.parseInt(request.getParameter("sno"));            Student stu = studentService.queryStudentBySno(sno);                request.setAttribute("student",stu);            request.getRequestDispatcher("updateinfo.jsp").forward(request,response);        }    }

addstudent.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>                            
    
             学号：
     
     
        姓名：
     
     
        年龄：
     
     
        地址：
     
     
        
     
     
    
    
    返回首页        

studentlist.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>                                    <%        String operateResult = (String) request.getAttribute("res");        if (operateResult!=null){          out.print(operateResult);        }else{          out.print("
");        }      %>      
    
      studentList = (List
     
      ) request.getAttribute("students");          for (Student student:studentList){        %>            
     
    
    
        <%          List
        <%          }        %>      
             
      
                 
学号
                 
姓名
                 
年龄
                 
操作
              
      
                     
<%=student.getStuNo()%>
                     
<%=student.getStuName()%>
                     
<%=student.getStuAge()%>
                     
修改
                     
删除
                  
     
    
      增加          

updateinfo.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>                            <%        Student stu = (Student) request.getAttribute("student");    %>        
    
                 学号：
     
     
            姓名：
     
     
            年龄：
     
     
            地址：
     
     
            
     
     
        
    
        返回首页