用JDBC写一个学生管理系统（添加、删除、修改、查询学生信息）

首先需要用Navicat Premium创建一个student表

用Java连接好MySQL数据库（需要copy一个mysql-connector-java-5.1.44-bin.jar包，该包可在网上找到）后，我们开始用Java写一个学生管理系统：
我们首选需要定义好添加、删除、修改、查询的方法，并把他们放到DBLink类中:

package com.zzuer.tool;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;public class DBLink {/*** 连接MySQL数据库实例test* 这里都需要引入java.sql.···jar包* 因为一下三个方法都要连接，所以直接定义一个连接的方法，为了简化代码* @return*/private Statement createStatement(){try {//加载驱动Class.forName("com.mysql.jdbc.Driver");//连接MySQL数据库，并返回Connection类型的对象String url = "jdbc:mysql://127.0.0.1/test";//此处链接本地的MySQL数据库中的实例testConnection connection = DriverManager.getConnection(url, "root", "root");//用户名和密码都为root（因计算机有所不同）//创建Statement对象，相当于 Navicat Premium 中 New Query，并返回return connection.createStatement();} catch (Exception e) {e.printStackTrace();}//若连接异常，则返回nullreturn null;}/*** 添加、删除、修改学生信息* @param sql 要执行的SQL语句*/public boolean update(String sql) {Connection connection = null;Statement statement = null;try {//调用createStatement()方法statement = createStatement();//执行SQL语句，并返回影响的行数int affect = statement.executeUpdate(sql);//无论怎样都要先执行finally里的语句之后，再执行return;return affect>0;} catch (Exception e) {e.printStackTrace();} finally {//释放资源close(connection,statement);}return false;}/*** 查询学生信息* @param sql*/public void select(String sql) {Connection connection = null;Statement statement = null;ResultSet resultset = null;try {statement = createStatement();//执行sql语句，并把学生信息存储在resultset资源中resultset = statement.executeQuery(sql);if(resultset.next()) {//next指向一行数据，执行完后跳到下一行，你可以近似把它看C语言中的“指针”String id = resultset.getString("id");String name = resultset.getString("name");String mobile = resultset.getString("mobile");String address = resultset.getString("address");System.out.println("学号："+id+",姓名："+name+",手机号："+mobile+",地址："+address);} else {System.out.println("系统异常，无法查询！");}} catch (Exception e) {e.printStackTrace();} finally {close(resultset,connection,statement);}}/*** 判断一个学生是否存在* 本质上还是查询学生信息，只是返回值不同，有则返回true，无则返回false* @param sql* @return*/public boolean exist(String sql) {Connection connection = null;Statement statement = null;ResultSet resultset = null;try {statement = createStatement();resultset = statement.executeQuery(sql);return resultset.next();//若存在则返回学生信息} catch (Exception e) {e.printStackTrace();} finally {//要及时释放资源close(resultset,connection,statement);}return false;//若不存在则返回false}/*** 定义一个close方法，主要是为了简化代码，* 因为上面三个都要释放资源* @param connection* @param statement*/private static void close(Connection connection,Statement statement) {try {if (connection != null) {connection.close();}} catch (SQLException e) {e.printStackTrace();}try {if (statement != null) {statement.close();}} catch (SQLException e) {e.printStackTrace();}}/*** 与上面close()方法属于重载* @param resultset* @param connection* @param statement*/private static void close(ResultSet resultset,Connection connection,Statement statement) {try {if (resultset != null) {resultset.close();}} catch (SQLException e) {e.printStackTrace();}close(connection,statement);}
}

主类：

import java.util.Scanner;import com.zzuer.tool.DBLink;public class Main {static DBLink db = new DBLink();public static void main(String[] args) {System.out.println("*********************************");System.out.println("*\t\t\t\t*");System.out.println("*\t欢迎使用学生信息管理系统\t*");System.out.println("*\t\t\t\t*");System.out.println("*********************************");while (true) {menu();}}static void menu() {System.out.println("1、添加学生信息");System.out.println("2、删除学生信息");System.out.println("3、修改学生信息");//地址传递System.out.println("4、查询学生信息");//nameSystem.out.println("请输入操作，以Enter键结束:");Scanner scanner = new Scanner(System.in);int option  = scanner.nextInt();switch (option) {case 1:{System.out.println("请输入学号：");String id = scanner.next();String sql = "select id from student where id='"+id+"'";if(db.exist(sql)) {System.out.println("该学号已存在，无法添加！");return;}System.out.println("请输入姓名：");String name = scanner.next();System.out.println("请输入手机号：");String mobile = scanner.next();System.out.println("请输入地址：");String address = scanner.next();sql = "insert into student(id,name,mobile,address) values ('"+id+"','"+name+"','"+mobile+"','"+address+"')";if(db.update(sql)) {System.out.println("添加成功！");return;}System.out.println("系统异常，添加失败");break;}case 2:{System.out.println("请输入要删除学生的学号：");String id = scanner.next();String sql = "select id from student where id='"+id+"'";if(!db.exist(sql)) {System.out.println("该学号不存在，无法删除！");return;}sql = "delete from student where id='"+id+"'";if(db.update(sql)) {System.out.println("删除成功！");return;}System.out.println("系统异常，删除失败！");break;}case 3:{System.out.println("请输入要修改学生的学号：");String id = scanner.next();String sql = "select id from student where id='"+id+"'";if(!db.exist(sql)) {System.out.println("该学号不存在，无法修改！");return;}System.out.println("请输入新的姓名：");String name = scanner.next();System.out.println("请输入新的手机号：");String mobile = scanner.next();System.out.println("请输入新的地址：");String address = scanner.next();sql = "update student set name='"+name+"',mobile='"+mobile+"',address='"+address+"' where id='"+id+"'";if(db.update(sql)) {System.out.println("修改成功！");}System.out.println("系统异常，修改失败！");break;}case 4:{System.out.println("请输入要查询学生的学号：");String id = scanner.next();String sql = "select id from student where id='"+id+"'";if(!db.exist(sql)) {System.out.println("该学号不存在，查询无果！");return;}sql = "select id,name,mobile,address from student where id='"+id+"'";db.select(sql);break;}default:System.out.println("I'm Sorry,there is not the "+option+" option,please try again.");}}
}