ThreadLocal

public class SequenceNumber {

        //①通過匿名內部類覆蓋ThreadLocal的initialValue()方法，指定初始值
    private static ThreadLocal<Integer> seqNum = new ThreadLocal<Integer>(){
        public Integer initialValue(){
            return 0;
        }
    };

        //②獲取下一個序列值
    public int getNextNum(){
        seqNum.set(seqNum.get()+1);
        return seqNum.get();
    }

    public static void main(String[ ] args)
    {
          SequenceNumber sn = new SequenceNumber();

         //③ 3個線程共享sn，各自產生序列號
         TestClient t1 = new TestClient(sn);
         TestClient t2 = new TestClient(sn);
         TestClient t3 = new TestClient(sn);
         t1.start();
         t2.start();
         t3.start();
    }
    private static class TestClient extends Thread
    {
        private SequenceNumber sn;
        public TestClient(SequenceNumber sn) {
            this.sn = sn;
        }
        public void run()
        {
                        //④每個線程打出3個序列值
            for (int i = 0; i < 3; i++) {
            System.out.println("thread["+Thread.currentThread().getName()+
"] sn["+sn.getNextNum()+"]");
            }
        }
    }
}

public class TopicDao {

  //①使用ThreadLocal保存Connection變量
private static ThreadLocal<Connection> connThreadLocal = new ThreadLocal<Connection>();
public static Connection getConnection(){

        //②如果connThreadLocal沒有本線程對應的Connection創建一個新的Connection，
        //並將其保存到線程本地變量中。
if (connThreadLocal.get() == null) {
            Connection conn = ConnectionManager.getConnection();
            connThreadLocal.set(conn);
              return conn;
        }else{
              //③直接返回線程本地變量
            return connThreadLocal.get();
        }
    }
    public void addTopic() {

        //④從ThreadLocal中獲取線程對應的
         Statement stat = getConnection().createStatement();
    }
}