ThreadLocal的簡單使用(讀書筆記)

     從ThreadLocal的名字上能夠看到,這是一個線程局部變量,也就是說,只有當前線程能夠訪問,既然是隻有當前線程能夠訪問的數據,天然是線程安全的.

public class ThreadLocalDemo {
    private static ThreadLocal<SimpleDateFormat> t1 = new ThreadLocal<>();

    public static class ParseDate implements Runnable {
        int i = 0;

        public ParseDate(int i) {
            this.i = i;
        }

        /**
         * When an object implementing interface <code>Runnable</code> is used
         * to create a thread, starting the thread causes the object's
         * <code>run</code> method to be called in that separately executing
         * thread.
         * <p>
         * The general contract of the method <code>run</code> is that it may
         * take any action whatsoever.
         *
         * @see Thread#run()
         */
        @Override
        public void run() {
            try {
                if (t1.get() == null)
                    t1.set(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
                Date t = t1.get().parse("2015-03-29 19:29:" + i % 60);
                System.out.println(i + ":" + t);
            } catch (ParseException e) {
                e.printStackTrace();
            }
        }

    }

    public static void main(String[] args) {
        ExecutorService es = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 1000; i++) {
            es.execute(new ParseDate(i));
        }

    }
}

     從這裏也能夠看到,爲每個線程人手分配一個對象工做並非有ThreadLocal來完成的.而是須要在應用層面保證的,若是在應用上爲每個線程分配了相同的對象實例,那麼ThreadLocal也不能保證線程安全,