用Java操作MySQL数据库

新建Maven项目

创建Maven项目

添加依赖

在pom.xml的标签里加上下面的内容
如果是MySQL 5.8那么的版本号是5.x.x, 例如5.1.49
如果是MySQL 8.0那么的版本号是8.x.x, 例如 8.0.28

<dependencies><!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.49</version></dependency></dependencies>

新建实体类

构建实体类, 类属性和表对应上, 方便来接收查询数据

举例

对于一个学生信息表

 CREATE TABLE student(id BIGINT,`name` VARCHAR(100),sn BIGINT,email VARCHAR(100),classId BIGINT)

新建学生类

public class Student {private int id;private String name;private long sn;private String email;private int classId;//记得自己加上toString()方法,和每个属性的getter和Setter方法
}

连接数据库查询内容

import com.mysql.jdbc.jdbc2.optional.MysqlDataSource;
import javax.sql.DataSource;
import java.sql.*;
import java.util.Scanner;public class Demo01_Connection {//先定义数据源对象, 待会用这个数据源操作数据库//先定义一个名字, 待会再具体实现private static DataSource dataSource = null;//定义自己数据库的各种属性, 方便全局修改// 数据库的用户名private static final String USER = "root";// 数据库的密码private static final String PASSWORD = "123456";// 数据库连接字符串(针对MySQL5)	本机数据库ip就是"localhost", 端口默认3306private static final String URL = "jdbc:mysql://数据库服务ip:端口号/数据库名?characterEncoding=utf-8&useSSL=false";// 如果是MySQL 8则是下面(mysql 8要加时区设置)//private static final String URL = "jdbc:mysql://数据库服务ip:端口号/数据库名?characterEncoding=utf8&useSSL=false&serverTimezone=Asia/Shanghai";public static void main(String[] args) {// 1. 初化始数据源,待会赋给上面定义的数据源MysqlDataSource myDataSource = new MysqlDataSource();// 2. 设置连接的参数myDataSource.setURL(URL);myDataSource.setUser(USER);myDataSource.setPassword(PASSWORD);// 3. 把构建好的Mysql数据源赋值给JDBC中的datasourcedataSource = myDataSource;//下面三个声明在try{}之外,方便finally也能识别Connection connection = null;PreparedStatement statement = null;ResultSet resultSet = null;try{//通过数据源获取一个数据库连接connection = dataSource.getConnection();//接收用户输入的值System.out.print("请输入姓名:");Scanner scanner = new Scanner(System.in);String sn = scanner.next();//定义SQL语句String sql = "select * from student where name = ?";// 获取一个预处理对象statement = connection.prepareStatement(sql);// 处理占位符的值,要匹配上类型,参数1代表第几个占位符,后者表示要被替换的内容statement.setString(1, sn);// 4. 执行SQLresultSet = statement.executeQuery();if (resultSet.next()) { //如果读取到了内容// 创建表示结果的JAVA对象Student student = new Student();student.setId(resultSet.getInt(1));student.setName(resultSet.getString(2));student.setSn(resultSet.getLong(3));student.setEmail(resultSet.getString(4));student.setClassId(resultSet.getInt(5));System.out.println(student);}}catch (SQLException e){e.printStackTrace();}finally {// 依次关闭资源,从后往前关if (resultSet != null) {try {resultSet.close();} catch (SQLException e) {e.printStackTrace();}}if (statement != null) {try {statement.close();} catch (SQLException e) {e.printStackTrace();}}if (connection != null) {try {connection.close();} catch (SQLException e) {e.printStackTrace();}}}}
}

将一系列操作封装成工具类

import com.mysql.jdbc.jdbc2.optional.MysqlDataSource;
import javax.sql.DataSource;
import java.sql.*;public class DBUtil {// 先定义一个数据源对象private static DataSource dataSource = null;// 数据库的用户名private static final String USER = "root";// 数据库的密码private static final String PASSWORD = "123456";// 数据库连接字符串private static final String URL = "jdbc:mysql://127.0.0.1:3306/java78?characterEncoding=utf-8&useSSL=false";static {// 初始化数据源,类加载时运行MysqlDataSource mysqlDataSource = new MysqlDataSource();mysqlDataSource.setURL(URL);mysqlDataSource.setUser(USER);mysqlDataSource.setPassword(PASSWORD);dataSource = mysqlDataSource;}// 用private 修饰构造方法，使外部不能new 这个类的对象private DBUtil() {}//获取数据库连接public static Connection getConnection () throws SQLException {return dataSource.getConnection();}//关闭对象并释放资源public static void close (ResultSet resultSet, PreparedStatement statement, Connection connection) {// 依次关闭对象，并释放资源if (resultSet != null) {try {resultSet.close();} catch (SQLException e) {e.printStackTrace();}}if (statement != null) {try {statement.close();} catch (SQLException e) {e.printStackTrace();}}if (connection != null) {try {connection.close();} catch (SQLException e) {e.printStackTrace();}}}
}

使用方法

省略了设置数据源参数和关闭数据源的操作

public class Main{public static void main(String[] args) {//声明三个对象Connection connection = null;PreparedStatement statement = null;ResultSet resultSet = null;try {// 1. 创建数据源并获取数据库连接connection = DBUtil.getConnection();// 2. 构造SQL语句String sql = "select id, name, sn, email, classId from student order by id ASC";// 使用SQL预处理对象处理SQLstatement = connection.prepareStatement(sql);// 3. 执行SQL并获取结果，如果是结果集把结果集转成java对象resultSet = statement.executeQuery();// 遍历结果集，处理查询到数据while (resultSet.next()) {Student student = new Student();student.setId(resultSet.getInt(1));student.setName(resultSet.getString(2));student.setSn(resultSet.getLong(3));student.setEmail(resultSet.getString(4));student.setClassId(resultSet.getInt(5));}// 打印结果System.out.println(student);} catch (SQLException e) {e.printStackTrace();} finally {// 4. 释放资源DBUtil.close(resultSet, statement, connection);}}
}

接收多个查询结果

import java.sql.*;
import java.util.ArrayList;
import java.util.List;public class Demo02_SelectAll {public static void main(String[] args) {// 查询到的所有学生信息放在List里List<Student> students = null;Connection connection = null;PreparedStatement statement = null;ResultSet resultSet = null;try {// 1. 创建数据源并获取数据库连接connection = DBUtil.getConnection();// 2. 构造SQL语句String sql = "select id, name, sn, email, classId from student order by id ASC";// 使用SQL预处理对象处理SQLstatement = connection.prepareStatement(sql);// 3. 执行SQL并获取结果，如果是结果集把结果集转成java对象resultSet = statement.executeQuery();// 遍历结果集，处理查询到数据while (resultSet.next()) {// 如果List为空则创建if (students == null) {students = new ArrayList<>();}// 解析结果集并封装成Student对象Student student = new Student();student.setId(resultSet.getInt(1));student.setName(resultSet.getString(2));student.setSn(resultSet.getLong(3));student.setEmail(resultSet.getString(4));student.setClassId(resultSet.getInt(5));// 加入到集合中students.add(student);}// 打印结果System.out.println(students);} catch (SQLException e) {e.printStackTrace();} finally {// 4. 释放资源DBUtil.close(resultSet, statement, connection);}}
}

数据更改

如果你想update, 那么把SQL语句即可, 原理是相同的,基本不用改Java代码. 例如改成Update student set age=10 where name=?
查询时statement.executeQuery(), 设置是statement.executeUpdate()

import java.sql.*;
import java.util.Scanner;public class Demo03_Delete {public static void main(String[] args) {Connection connection = null;PreparedStatement statement = null;try {// 1. 获取数据库连接connection = DBUtil.getConnection();// 2. 构建SQLString sql = "delete from student where name = ?";// 接收用户的输入System.out.print("请输入要删除的同学姓名:");Scanner scanner = new Scanner(System.in);String name = scanner.next();// 3. 对SQL进行处理，并替换占位符statement = connection.prepareStatement(sql);//替换参数: 1代表第一个问号, name代表填入的数据statement.setString(1, name);// 4. 执行SQL并获取结果int row = statement.executeUpdate();if (row <= 0) {System.out.println("删除失败.");} else {System.out.println("删除成功");}} catch (SQLException e) {e.printStackTrace();} finally {// 释放资源DBUtil.close(null, statement, connection);}}
}

插入数据

import java.sql.*;
import java.util.Scanner;public class Demo04_Insert {public static void main(String[] args) {Connection connection = null;PreparedStatement statement = null;try {// 1. 获取数据库连接connection = DBUtil.getConnection();// 2. 构建SQLString sql = "insert into student values (?, ?, ?, ?, ?)";// 接收用户的输入Scanner scanner = new Scanner(System.in);System.out.print("请输入要添加的同学Id:");int id = scanner.nextInt();// 姓名System.out.print("请输入学生的姓名:");String name = scanner.next();// 学号System.out.print("请输入学生的学号->");long sn = scanner.nextLong();// 邮箱System.out.print("请输入学生的邮箱->");String email = scanner.next();// 班级编号System.out.print("请输入学生的班级编号->");int classId = scanner.nextInt();// 3. 对SQL进行处理statement = connection.prepareStatement(sql);// 替换占位符statement.setInt(1, id);statement.setString(2, name);statement.setLong(3, sn);statement.setString(4, email);statement.setInt(5, classId);// 4. 执行SQL并获取结果int row = statement.executeUpdate();if (row <= 0) {System.out.println("添加失败.");} else {System.out.println("添加成功");}} catch (SQLException e) {e.printStackTrace();} finally {// 释放资源DBUtil.close(null, statement, connection);}}
}