读写锁接口实例-通过ReadWriteLock实现一个简单的缓存

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class Cache {
private static final Map<String, Object>    map = new HashMap<String, Object>();
private static final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
private static final Lock                   r   = rwl.readLock();
private static final Lock                   w   = rwl.writeLock();

public static final Object get(String key) {
r.lock();
try {
return map.get(key);
} finally {
r.unlock();
}
}

public static final Object put(String key, Object value) {
w.lock();
try {
return map.put(key, value);
} finally {
w.unlock();
}
}

public static final void clear() {
w.lock();
try {
map.clear();
} finally {
w.unlock();
}
}
}