请问：用单例模式封装了数据库连接的connection，需要关闭吗

请教：用单例模式封装了数据库连接的connection，需要关闭吗？
请教：用单例模式封装了数据库连接的connection，需要关闭吗？如果关闭会不会出问题，比如说：A线程拿到了连接connection，B线程同时也拿到了。A的事务完成后提交了，把connection关闭，B线程会不会出问题？

Java code

package com.gzsoft.secondWeb.util;import java.io.IOException;import java.io.InputStream;import java.sql.*;import java.util.Properties;/** * 单例的模式 * @author lyp * */public class DB {    private static Connection conn=null;private static String driver;private static String connectionURL;private static String username;private static String password;static{    Properties p=new Properties();    InputStream in=DB.class.getClassLoader().getResourceAsStream("connection.properties");    try {        p.load(in);        driver=p.getProperty("driver");        connectionURL=p.getProperty("connection_URL");        username=p.getProperty("username");        password=p.getProperty("password");            } catch (IOException e) {    }    }public static Connection getConnetion(){    if(conn==null){        try {                        Class.forName(driver).newInstance();            DriverManager.getConnection(connectionURL,username,password);            System.out.print("success to connect to database!");        } catch (InstantiationException e) {           e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        } catch (ClassNotFoundException e) {           System.out.println("can't find the Driver");        } catch (SQLException e) {           System.out.println("fail to connect to database!");        }            }    return conn;    }public static void closeAll(ResultSet rs,PreparedStatement psmt,Connection conn){    if(rs!=null){        try {            rs.close();            rs=null;        } catch (SQLException e) {            e.printStackTrace();        }    }    if(psmt!=null){        try {            psmt.close();            psmt=null;        } catch (SQLException e) {           e.printStackTrace();        }    }    if(conn!=null){        try {            conn.close();            conn=null;        } catch (SQLException e) {           e.printStackTrace();        }    }    }    public static void main(String[] args) {        System.out.println("driver:"+driver+"  connURL:"+connectionURL+"  username:"+username+"  password:"+password);        getConnetion();    }}