增删查改CURD实战（笔记ಥ_ಥ）
温故而知新，可以为师矣
主体
MySQL数据库：
Student表，存放Student信息，id为自增主键。
从左到右各字段分别是int,String,Float和Date。
实现功能：增删查改
需要导入的jar包：
Java包及其作用
| 包名 | 作用 |
|---|---|
| entity | 对象实体，用于实例化对象 |
| servlet | 接受请求，发出响应 |
| repository | 数据库操作 |
| filter | 过滤器，对servlet进行过滤操作（设置编码） |
| util | 工具包，存放封装的方法 |
Java类及其作用
结构：
1.entity包
Student类：实例化Student对象，用于传递表信息。
package com.southwind.entity;
import java.util.Date;
public class Student {
private Integer id;
private String name;
private Float score;
private Date birthday;
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", score=" + score +
", birthday=" + birthday +
'}';
}
public Student(Integer id, String name, Float score, Date birthday) {
this.id = id;
this.name = name;
this.score = score;
this.birthday = birthday;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Float getScore() {
return score;
}
public void setScore(Float score) {
this.score = score;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
}
2.servlet包
StudentServlet类：处理客户端发来的请求以及发出响应，请求到来前首先会经过过滤器。
package com.southwind.servlet;
import com.southwind.entity.Student;
import com.southwind.repository.StudentRepository;
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("/student")
public class StudentServlet extends HttpServlet {
StudentRepository studentRepository = new StudentRepository();
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String method = req.getParameter("method");
if(method == null){
method = "findAll";
}
switch (method){
case "findAll":
List<Student> list = studentRepository.findAll();
req.setAttribute("list",list);
req.getRequestDispatcher("index.jsp").forward(req,resp);
break;
case "deleteById":
//取出id
String idStr = req.getParameter("id");
Integer id = Integer.parseInt(idStr);
studentRepository.delete(id);
resp.sendRedirect("/student");
//根据id删除
break;
case "findById":
//取出id
idStr = req.getParameter("id");
id = Integer.parseInt(idStr);
req.setAttribute("student",studentRepository.findById(id));
req.getRequestDispatcher("update.jsp").forward(req,resp);
break;
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String method = req.getParameter("method");
switch (method){
case "update":
String idStr = req.getParameter("id");
Integer id = Integer.parseInt(idStr);
String name = req.getParameter("name");
String scoreStr = req.getParameter("score");
Float score = Float.parseFloat(scoreStr);
studentRepository.update(id,name,score);
break;
case "add":
name = req.getParameter("name");
scoreStr = req.getParameter("score");
score = Float.parseFloat(scoreStr);
studentRepository.add(name,score);
break;
}
resp.sendRedirect("/student");
}
}
3.filter包
CharacterFilter类：把servlet的请求过滤，处理请求的编码，使之传递中文不出现乱码
package com.southwind.filter;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;
@WebFilter("/student")
public class CharaterFilter implements Filter {
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
servletRequest.setCharacterEncoding("UTF-8");
filterChain.doFilter(servletRequest,servletResponse);
}
}
4.util包
JDBCUtil类：集中处理数据库的连接和关闭，减少代码重复。给StudentRepository方法调用。
package com.southwind.util;
import java.sql.*;
public class JDBCTools {
private static Connection connection = null;
private static String url = "jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=UTF-8";
private static String user = "root";
private static String password = "admin";
static {
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (Exception e) {
e.printStackTrace();
}
}
public static Connection getConnection() {
try {
connection = DriverManager.getConnection(url,user,password);
} catch (SQLException throwables) {
throwables.printStackTrace();
}
return connection;
}
public static void release(Connection connection, Statement statement, ResultSet resultSet){
if(connection != null){
try {
connection.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if(statement != null){
try {
statement.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if(resultSet != null){
try {
resultSet.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
public static void main(String[] args) {
getConnection();
System.out.println(connection);
}
}
5.repository包
StudentRepository类：处理增删查改操作，使用本类的方法前要实例化StudentRepository对象
package com.southwind.repository;
import com.southwind.entity.Student;
import com.southwind.util.JDBCTools;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.List;
import java.util.concurrent.ConcurrentNavigableMap;
public class StudentRepository {
//写关于Student的数据库操作
public List<Student> findAll(){
List<Student> list = new ArrayList<>();
Connection connection = null;
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
//查询数据库，遍历对象
connection = JDBCTools.getConnection();
String sql = "select * from student";
try {
preparedStatement = connection.prepareStatement(sql);
resultSet = preparedStatement.executeQuery();
Student student = null;
while(resultSet.next()){
Integer id = resultSet.getInt(1);
String name = resultSet.getString(2);
Float score = resultSet.getFloat(3);
Date birthday = resultSet.getDate(4);
student = new Student(id,name,score,birthday);
list.add(student);
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
JDBCTools.release(connection,preparedStatement,resultSet);
}
return list;
}
public void delete(Integer id){
Connection connection = null;
PreparedStatement preparedStatement = null;
connection = JDBCTools.getConnection();
String sql = "delete from student where id = ?";
try {
preparedStatement = connection.prepareStatement(sql);
preparedStatement.setInt(1,id);
preparedStatement.executeUpdate();
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
JDBCTools.release(connection,preparedStatement,null);
}
}
public Student findById(Integer id){
Student student = null;
Connection connection = null;
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
connection = JDBCTools.getConnection();
String sql = "select * from student where id = ?";
try {
preparedStatement = connection.prepareStatement(sql);
preparedStatement.setInt(1,id);
resultSet = preparedStatement.executeQuery();
while(resultSet.next()){
Integer id1 = resultSet.getInt(1);
String name = resultSet.getString(2);
Float score = resultSet.getFloat(3);
Date birthday = resultSet.getDate(4);
student = new Student(id1,name,score,birthday);
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
JDBCTools.release(connection,preparedStatement,resultSet);
}
return student;
}
public void update(Integer id,String name,Float score){
Connection connection = null;
PreparedStatement preparedStatement = null;
Student student = null;
connection = JDBCTools.getConnection();
String sql = "update student set name = ?,score = ? where id = ?";
try {
preparedStatement = connection.prepareStatement(sql);
preparedStatement.setString(1,name);
preparedStatement.setFloat(2,score);
preparedStatement.setInt(3,id);
preparedStatement.executeUpdate();
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
JDBCTools.release(connection,preparedStatement,null);
}
}
public void add(String name,Float score){
Connection connection = null;
PreparedStatement preparedStatement = null;
connection = JDBCTools.getConnection();
String sql = "insert into student(name,score,birthday) values(?,?,?)";
try {
preparedStatement = connection.prepareStatement(sql);
preparedStatement.setString(1,name);
preparedStatement.setFloat(2,score);
preparedStatement.setDate(3,new java.sql.Date(System.currentTimeMillis()));
preparedStatement.executeUpdate();
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
JDBCTools.release(connection,preparedStatement,null);
}
}
public static void main(String[] args) {
StudentRepository studentRepository = new StudentRepository();
System.out.println(studentRepository.findAll());
System.out.println(new java.sql.Date(System.currentTimeMillis()));
}
}
前端jsp页面
1、index.jsp
作用：显示所有学生信息
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%--
Created by IntelliJ IDEA.
User: shinelon
Date: 2020/6/26
Time: 23:09
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>
<h1>成绩管理系统</h1>
<form action="/student" method="get">
<input value="查询学生信息" type="submit" />
<a href="add.jsp" >添加学生信息</a>
</form>
<table>
<tr>
<th>编号</th>
<th>姓名</th>
<th>成绩</th>
<th>注册日期</th>
<th>操作</th>
</tr>
<c:forEach items="${list}" var="student">
<tr>
<td>${student.id}</td>
<td>${student.name}</td>
<td>${student.score}</td>
<td>${student.birthday}</td>
<td>
<a href="/student?method=deleteById&id=${student.id}">删除</a>
<a href="/student?method=findById&id=${student.id}">修改</a>
</td>
</tr>
</c:forEach>
</table>
</body>
</html>
显示：（单击查询学生信息后）
2、add.jsp
作用：添加学生信息
<%--
Created by IntelliJ IDEA.
User: shinelon
Date: 2020/6/27
Time: 11:05
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<form method="post" action="/student">
姓名：<input type="text" name="name" /><br/>
成绩：<input type="text" name="score" /><br/>
<input type="hidden" name="method" value="add" />
<input type="submit" value="提交" />
</form>
</body>
</html>
显示：（注意：功能简化，暂不支持提交Date）
3、update.jsp
作用：更新学生信息
<%--
Created by IntelliJ IDEA.
User: shinelon
Date: 2020/6/27
Time: 8:34
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<form action="/student" method="post">
编号：<input type="text" name="id" value="${student.id}" readonly/><br/>
姓名：<input type="text" name="name" value="${student.name}" /><br/>
成绩：<input type="text" name="score" value="${student.score}" /><br/>
日期：<input type="text" name="birthday" value="${student.birthday}" readonly/><br/>
<input type="hidden" name="method" value="update" />
<input type="submit" value="提交" />
</form>
</body>
</html>
显示：（只允许修改姓名与成绩）
