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<Student> queryAll(){
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
List<Student> 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<Student> 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<Student> 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" %>
<html>
<head>
<title>添加学生</title>
</head>
<body>
<form action="AddStudentServlet" method="post">
学号：<input type="number" name="stuNo"><br>
姓名：<input type="text" name="stuName"><br>
年龄：<input type="number" name="stuAge"><br>
地址：<input type="text" name="stuAddress"><br>
<input type="submit" value="提交"><br>
</form>
<a href="QueryAllStudents">返回首页</a>
</body>
</html>studentlist.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>学生信息列表</title>
</head>
<body>
<%
String operateResult = (String) request.getAttribute("res");
if (operateResult!=null){
out.print(operateResult);
}else{
out.print("<br>");
}
%>
<table border="1px">
<tr>
<th>学号</th>
<th>姓名</th>
<th>年龄</th>
<th>操作</th>
</tr>
<%
List<Student> studentList = (List<Student>) request.getAttribute("students");
for (Student student:studentList){
%>
<tr>
<td><%=student.getStuNo()%></td>
<td><%=student.getStuName()%></td>
<td><%=student.getStuAge()%></td>
<td><a href="QueryStudentBySno?sno=<%=student.getStuNo()%>">修改</a></td>
<td><a href="DeleteStudentServlet?sno=<%=student.getStuNo()%>">删除</a></td>
</tr>
<%
}
%>
</table>
<a href="addstudent.jsp">增加</a>
</body>
</html>updateinfo.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>学生个人信息</title>
</head>
<body>
<%
Student stu = (Student) request.getAttribute("student");
%>
<form action="UpdateStudentBySnoServlet" method="post">
学号：<input type="number" name="sno" value="<%=stu.getStuNo()%>"><br>
姓名：<input type="text" name="sname" value="<%=stu.getStuName()%>"><br>
年龄：<input type="number" name="sage" value="<%=stu.getStuAge()%>"><br>
地址：<input type="text" name="saddress" value="<%=stu.getStuAddress()%>"><br>
<input type="submit" value="提交"><br>
</form>
<a href="QueryAllStudents">返回首页</a>
</body>
</html>