例子

public class SeqGen {
    private static ThreadLocal<Integer> seqNum = new ThreadLocal<Integer>() {
        @Override
        public Integer initialValue() {
            return 0;
        }
    };

    public int getNextNum() {
        seqNum.set(seqNum.get() + 1);
        return seqNum.get();
    }
}

public class TestThread implements Runnable {
    private SeqGen sn;

    public TestThread(SeqGen sn) {
        this.sn = sn;
    }

    public void run() {
        for (int i = 0; i < 3; i++) {
            String str = Thread.currentThread().getName() + "-->"
                    + sn.getNextNum();
            System.out.println(str);
        }
    }
}

public class Test {
    public static void main(String[] args) {
        SeqGen sn = new SeqGen();
        TestThread tt1 = new TestThread(sn);
        TestThread tt2 = new TestThread(sn);
        TestThread tt3 = new TestThread(sn);
        Thread t1 = new Thread(tt1);
        Thread t2 = new Thread(tt2);
        Thread t3 = new Thread(tt3);
        t1.start();
        t2.start();
        t3.start();
    }
}

输出结果：
Thread-2-->1
Thread-2-->2
Thread-2-->3
Thread-1-->1
Thread-0-->1
Thread-0-->2
Thread-0-->3
Thread-1-->2
Thread-1-->3

资料来源：

(1) 理解ThreadLocal http://blog.csdn.net/qjyong/article/details/2158097

(2) ThreadLocal的几种误区 http://www.blogjava.net/jspark/archive/2006/08/01/61165.html

(3) 正确理解ThreadLocal http://lujh99.iteye.com/blog/103804