为什么自定义连接池,加了锁还是不安全?

╰+攻爆jí腚メ 2024-02-18 15:20 26阅读 0赞

import java.sql.Connection;  
import java.sql.DriverManager;  
import java.sql.SQLException;  
import java.util.LinkedList;  
  
  
  
  
  
  
import com.mysql.jdbc.Driver;  
  
  
/\*\*  
\* 自定义数据库连接池  
\* @author Shinelon  
\*  
\*/  
public class Demo05 \{  
private static LinkedList<Connection> connPool=null;  
//注册驱动  
static\{  
try \{  
DriverManager.registerDriver(new Driver());  
connPool = new LinkedList<Connection>();  
\} catch (SQLException e) \{  
// TODO Auto-generated catch block  
e.printStackTrace();  
\}  
\}  
//构造方法  
public Demo05()\{  
for (int i = 0; i <10; i++) \{  
Connection conn;  
try \{  
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/exam?user=root&password=321");  
connPool.add(conn);  
\} catch (SQLException e) \{  
// TODO Auto-generated catch block  
e.printStackTrace();  
\}  
\}  
\}  
  
public synchronized Connection getConnection()\{  
//返回最后一个并移除  
return connPool.removeLast();  
\}  
public void closeConn(Connection conn)\{  
//关闭时,存回连接  
connPool.addFirst(conn);  
\}

多线程测试:

import java.sql.Connection;  
  
  
public class Demo06 \{  
  
  
public static void main(String\[\] args) \{  
final Demo05 demo05 = new Demo05();  
  
  
// 创建两个线程  
for (int i = 0; i < 2; i++) \{  
new Thread(new Runnable() \{  
@Override  
public void run() \{  
for (int i = 0; i < 4; i++) \{  
Connection conn = demo05.getConnection();  
try \{  
Thread.currentThread().sleep(100);  
\} catch (InterruptedException e) \{  
// TODO Auto-generated catch block  
e.printStackTrace();  
\}  
System.out.println(i+":"+Thread.currentThread().getName()+":"+conn.toString());  
//demo05.closeConn(conn);  
\}  
\}  
\}).start();  
\}  
\}  
\}

结果:

**0:Thread-1:com.mysql.jdbc.JDBC4Connection@933c07  
0:Thread-0:com.mysql.jdbc.JDBC4Connection@933c07**  
1:Thread-0:com.mysql.jdbc.JDBC4Connection@49ff3f  
1:Thread-1:com.mysql.jdbc.JDBC4Connection@14ac54  
2:Thread-1:com.mysql.jdbc.JDBC4Connection@13de2bd  
2:Thread-0:com.mysql.jdbc.JDBC4Connection@1f12373  
3:Thread-0:com.mysql.jdbc.JDBC4Connection@4e94a4  
3:Thread-1:com.mysql.jdbc.JDBC4Connection@100b3c2

求大神解答!