对非线程安全的集合进行了读写锁控制

  publicclass RWDictionary {

private final Map<String, String> m = new TreeMap<String, String>();
    private final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
    private final Lock r = rwl.readLock();
    private final Lock w = rwl.writeLock();

    public String get(String key) {
        r.lock();
        try {
            return m.get(key);
        } finally {
            r.unlock();
        }
    }

    public Object[] allKeys() {
        r.lock();
        try {
            return m.keySet().toArray();
        } finally {
            r.unlock();
        }
    }

    public String put(String key, String value) {
        w.lock();
        try {
            return m.put(key, value);
        } finally {
            w.unlock();
        }
    }

    public void clear() {
        w.lock();
        try {
            m.clear();
        } finally {
            w.unlock();
        }
    }
}