系统刚启动时（MySQL数据库还未启动），无法连接MySQL的解决方案（使用JDBC失败重连机制）

下方是一个开机自启动的ServerSocket服务 ，由于启动比MySQL数据库快，导致数据库连接池创建失败。因此增加了testJDBC()方法进行递归，直至连接成功。

package socket;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
//import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeUnit;

import org.apache.tomcat.jdbc.pool.DataSource;

/**
 * 使用长连接2001端口（新项目20231228）
 * @author Administrator
 *
 */
public class M3_5 {

	public static void main(String[] args) {
		
		/* 不成功重连jdbc */
		testJDBC();
		// 配置数据源
		DataSource dataSource = new DataSource();
		dataSource.setUrl("jdbc:mysql://127.0.0.1:3306/plc?characterEncoding=UTF8");
		dataSource.setUsername("root");
		dataSource.setPassword("111111");
		dataSource.setDriverClassName("com.mysql.cj.jdbc.Driver");
//		dataSource.setTestOnBorrow(true);
//		dataSource.setTestOnReturn(true);
		dataSource.setValidationQuery("select 1 from dual");
		dataSource.setValidationInterval(3600000);
		dataSource.setTestWhileIdle(true);
		dataSource.setTimeBetweenEvictionRunsMillis(3600000);
		dataSource.setMinIdle(1);
		dataSource.setInitialSize(1);
		System.out.println(dataSource.getMinIdle());
		System.out.println(dataSource.getMaxIdle());
		System.out.println(dataSource.getMaxActive());
		System.out.println(dataSource.getIdle());
		System.out.println(dataSource.getActive());
		
		try(ServerSocket s = new ServerSocket(2001)){
			ExecutorService pool = Executors.newFixedThreadPool(4);
			while(true) {
				Socket socket = s.accept();
				pool.execute(new Task(socket,dataSource));
				ThreadPoolExecutor t = (ThreadPoolExecutor)pool;
				System.out.println("active:"+t.getActiveCount());
				System.out.println("core:"+t.getCorePoolSize());
				System.out.println("TaskCount"+t.getTaskCount());
//				System.out.println("CompletedTaskCount:"+t.getCompletedTaskCount());
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
		
	}
	/**
	 * 不成功重连功能
	 */
	private static void testJDBC() {
        // 数据库连接信息
        String url = "jdbc:mysql://127.0.0.1:3306/plc?characterEncoding=UTF8";
        String user = "root";
        String password = "111111";
 
        try {
            // 加载数据库驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            
            // 建立连接
            Connection connection = DriverManager.getConnection(url, user, password);
            
            // 检查连接是否成功
            if (connection != null && !connection.isClosed()) {
                System.out.println("数据库连接成功！");
            } else {
                System.out.println("数据库连接失败！");
            }
            
            // 关闭连接
            connection.close();
        } catch (ClassNotFoundException e) {
            System.out.println("数据库驱动未找到！");
        } catch (SQLException e) {
            System.out.println("数据库连接异常：" + e.getMessage());
            try {
            	System.out.println("等待5秒后重试");
				TimeUnit.SECONDS.sleep(5);
			} catch (InterruptedException e1) {
				e1.printStackTrace();
			}
            testJDBC();
        } catch (Exception e) {
            System.out.println("未知异常：" + e.getMessage());
        }
	}

}

核心在于，jdbc连接失败报SQLException异常，在该异常捕获后，延迟5秒重新调用testJDBC方法，如此递归，直至成功。