Java连接MySQL以及出现的问题

package sqltest;
import java.sql.*;
public class TestSql {
	public static void main(String[] args) {
	//加载驱动程序
		try {
			Class.forName("com.mysql.cj.jdbc.Driver");
			System.out.println("驱动程序加载成功");
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
		//链接数据库
		String str = "jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=UTF-8&userSSL=false&serverTimezone=GMT%2B8";	
		Connection conn=null;
		try {
			conn=DriverManager.getConnection(str,"root","123456");
			if (!conn.isClosed()) {
				System.out.println("连接数据库成功");
			}
		} catch (SQLException e) {
			System.out.println("链接数据库失败: "+e.getMessage());
		}
		try{
		Statement stmt = conn.createStatement();
	    ResultSet rs = stmt.executeQuery("select user_name,age from student");
        while(rs.next()){//如果对象中有数据，就会循环打印出来
	          System.out.println(rs.getString("user_name")+","+rs.getInt("age"));
      }
		}catch(SQLException e){
			System.out.println("查询失败");
		}
	}
}