不使用任何工具类手动连接

package com.oracle.jdbc;import java.sql.*;/***jdbc查询 jdbc数据库下，user表中所有数据并打印在控制台* jdbc操作数据库步骤*  1注册驱动*  2创建数据库连接对象*  3获取传输器对象*  4执行sql*  5处理结果集*  6释放资源*/public class JDBCDemo1 {public static void main(String[] args) throws ClassNotFoundException, SQLException {Class.forName("com.mysql.cj.jdbc.Driver");String root = "root";String password = "root";// String url = "jdbc:mysql://localhost:3306/jdbc?useSSL=false&serverTimezone=UTC&useUnicode=true&characterEncoding=UTF-8";String url = "jdbc:mysql://localhost:3306/jdbc";Connection connection = DriverManager.getConnection(url, root, password);System.out.println(connection);Statement statement = connection.createStatement();String sql = "select * from user";ResultSet resultSet = statement.executeQuery(sql);while(resultSet.next()){int id = resultSet.getInt("id");String name = resultSet.getString("name");String gender = resultSet.getString("gender");int age = resultSet.getInt("age");String address = resultSet.getString("address");System.out.println(id +"," +name +","+gender+","+age+","+address );}resultSet.close();statement.close();connection.close();}
}

初步封装一下，变成工具类

package com.march.mysql0314;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;public class DBUtil {private static final String URL = "jdbc:mysql://localhost:3306/empdb?useSSL=false&characterEncoding=utf8&serverTimezone=Asia/Shanghai";private static final String U = "com.mysql.cj.jdbc.Driver";private static final String USERNAME = "root";private static final String PASSWORLD = "root";private static Connection connection = null;private DBUtil(){};public static Connection getConnection() throws SQLException, ClassNotFoundException {if (connection == null || connection.isClosed()){Class.forName(U);connection = DriverManager.getConnection(URL, USERNAME, PASSWORLD);}return connection;}public static void closeConnection(){try {if (!connection.isClosed()&&connection == null){connection.close();}} catch (SQLException e) {e.printStackTrace();}}}

使用属性集文件连接，方便改写用户登录的数据

package com.march.mysql0314;import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;public class DBUtilPro {private static Connection connection = null;private DBUtilPro(){};private static Properties properties = new Properties();static{try(InputStream inputStream = DBUtilPro.class.getResourceAsStream("/mysql.properties");){properties.load(inputStream);} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}public static Connection getConnection() throws SQLException, ClassNotFoundException {if (connection == null || connection.isClosed()){Class.forName(properties.getProperty("Driver"));connection = DriverManager.getConnection(properties.getProperty("URL"),properties.getProperty("USERNAME"),properties.getProperty("PASSWORLD"));}return connection;}public static void closeConnection(){try {if (!connection.isClosed()&&connection == null){connection.close();}} catch (SQLException e) {e.printStackTrace();}}
}

使用线程集合ThreadLocal实现同一事务的同一连接

package com.march.mysql0314;import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;public class DBUtilProMax {private DBUtilProMax(){};private static Properties properties = new Properties();private static ThreadLocal<Connection> threadLocal = new ThreadLocal<>();static{try(InputStream inputStream = DBUtil.class.getResourceAsStream("/mysql.properties");){properties.load(inputStream);} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}public static Connection getConnection() throws SQLException, ClassNotFoundException {Connection connection = threadLocal.get();if (connection == null || connection.isClosed()){Class.forName(properties.getProperty("Driver"));connection = DriverManager.getConnection(properties.getProperty("URL"),properties.getProperty("USERNAME"),properties.getProperty("PASSWORLD"));threadLocal.set(connection);}return connection;}public static void closeConnection(){Connection connection = threadLocal.get();try {if (!connection.isClosed()&&connection == null){connection.close();}} catch (SQLException e) {e.printStackTrace();}}
}

使用德鲁伊连接池

package com.march.mysql0314;import com.alibaba.druid.pool.DruidDataSourceFactory;import javax.sql.DataSource;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;public class DButilFinally {// 私有的构造方法private DButilFinally(){}//---1定义静态变量 : Propertiesprivate  static Properties pro =new Properties();//========================> 1 创建DataSource对象private  static DataSource ds = null;//---2使用静态代码块,读取配置文件static{try(//==>2 获取流, 文件存储在src目录下InputStream in = DBUtil.class.getResourceAsStream("/druid.properties");){//把IO中的属性集加载到properties对象中pro.load(in);//==================>获取数据源对象ds = DruidDataSourceFactory.createDataSource(pro);} catch (Exception e) {e.printStackTrace();}}// ---- 使用ThreadLocal存储连接对象//1 定义ThreadLocalprivate  static ThreadLocal<Connection> local = new ThreadLocal<>();/*** 获取连接的方法* @return* @throws SQLException* @throws ClassNotFoundException*/public  static Connection getConn() throws SQLException, ClassNotFoundException {// --2 从ThreadLocal中获取连接对象Connection conn = local.get();if(conn ==null  || conn.isClosed()){//=============================>通过DataSource获取连接对象conn = ds.getConnection();// ---3 向ThreadLocal中存储连接对象local.set(conn);;}return  conn;}/*** 关闭连接的方法*/public static   void closeConn(){//  // --2 从ThreadLocal中获取连接对象Connection conn = local.get();try {if(conn!=null  && !conn.isClosed()){  //conn不是null ,同时也没有关闭conn.close();}} catch (SQLException e) {e.printStackTrace();}finally {// -- 删除ThreadLocal中存储的数据local.remove();}}}