ThreadLocal简单使用案例

        业务场景：保存业务数据表的时候，同时记录下日志。

import java.sql.Connection;
import java.sql.DriverManager;public class DBUtil {// 数据库配置private static final String driver = "com.mysql.jdbc.Driver";private static final String url = "jdbc:mysql://localhost:3306/test";private static final String username = "root";private static final String password = "root";private static Connection conn = null;public static Connection getDbConnection() {try {Class.forName(driver);conn = DriverManager.getConnection(url, username, password);} catch (Exception e) {e.printStackTrace();}return conn;}// 关闭数据库连接public static void closeDbConnection() {try {if (conn != null) {conn.close();}} catch (Exception e) {e.printStackTrace();}}
}

import com.example.springboottest.util.DBUtil;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.text.SimpleDateFormat;
import java.util.Date;public class ThreadLocalTest3 {private static final String UPDATE_SQL = "update t_test set num = ? where id = ?";private static final String INSERT_SQL = "insert into log (id, desc) values (?, ?)";public static void main(String[] args) {ThreadLocalTest3 service = new ThreadLocalTest3();service.updateBusiness(1, 3000);}public void updateBusiness(int id, int num) {try {// 获取连接Connection conn = DBUtil.getDbConnection();conn.setAutoCommit(false); // 关闭自动提交事务（开启事务）// 执行操作updateBizData(conn, UPDATE_SQL, id, num);// 插入日志insertLog(conn, INSERT_SQL, "描述"); // 提交事务conn.commit();} catch (Exception e) {e.printStackTrace();} finally {// 关闭连接DBUtil.closeDbConnection();}}private void updateBizData(Connection conn, String updateSQL, int id, int num) throws Exception {PreparedStatement pstmt = conn.prepareStatement(updateSQL);pstmt.setInt(1, id);pstmt.setLong(2, num);int rows = pstmt.executeUpdate();if (rows != 0) {System.out.println("业务数据更新成功!");}}private void insertLog(Connection conn, String insertSQL, String desc) throws Exception {PreparedStatement pstmt = conn.prepareStatement(insertSQL);pstmt.setString(1, new SimpleDateFormat("yyyy-MM-dd HH:mm:ss SSS").format(new Date()));pstmt.setString(2, desc);int rows = pstmt.executeUpdate();if (rows != 0) {System.out.println("日志插入成功!");}}
}

        上面的代码直接运行肯定是没有问题的，但是如果在多线程下面去跑，就会报数据库连接关闭的错误。原因很简单，多线程下执行，可能一个线程刚获取到连接另一个线程就已经把连接关闭了，所以就会导致这样的问题，要解决这个问题，ThreaLocal就是一个很好的选择，只需要改调整下DBUtil里面获取连接的代码即可。如下代码所示：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;public class DBUtil {// 数据库配置private static final String driver = "com.mysql.jdbc.Driver";private static final String url = "jdbc:mysql://localhost:3306/test";private static final String username = "root";private static final String password = "root";private static ThreadLocal<Connection> connContainer = new ThreadLocal<Connection>(){//初始化connContainer里面的值，如果不重写则为null；@Overrideprotected Connection initialValue() {try {Class.forName(driver);return  DriverManager.getConnection(url, username, password);} catch (SQLException e) {throw new RuntimeException(e);}}};// 获取连接public static Connection getDbConnection() {Connection conn = connContainer.get();try {if (conn == null) {Class.forName(driver);conn = DriverManager.getConnection(url, username, password);}} catch (Exception e) {e.printStackTrace();} finally {connContainer.set(conn);}return conn;}// 关闭连接public static void closeDbConnection() {Connection conn = connContainer.get();try {if (conn != null) {conn.close();}} catch (Exception e) {e.printStackTrace();} finally {connContainer.remove();}}
}