新开了个项目可以连mysql，但是原本的项目连接不上去

package com.example.sqltest.Tool;

import java.sql.Connection;
import java.sql.DriverManager;

public class SqlTool {
    private static String driver;
    private static String url;
    private static String username;
    private static String password;
    private static Connection connection;
    public static void getconcetion(){
        Thread tg=new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    driver="com.mysql.jdbc.Driver";
                    url="jdbc:mysql://172.18.56.110:3306/exam";
                    username="bill";
                    password="111111";
                    Class.forName(driver);
                    connection= DriverManager.getConnection(url,username,password);
                    for(int i=0;i<100;i++) System.out.println("线程加载"+i);
                    System.out.println(String.valueOf(connection));

                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        });
        tg.start();
    }
}