Are Locks AutoCloseable?

I think a simple util method which takes a lock and a Runnable is better than using the try-with-resource statement with locks.

Like this:

public static void locked(Lock lock, Runnable r) {
    lock.lock();

    try {
        r.run();
    } finally {
        lock.unlock();
    }
}

Usage example:

locked(lock, () -> {
    // Do your stuff
});

Advantages:

• There is no dummy variable created for the try-with-resource.
• I think it is very clear.

Disadvantage

• A Runnable instance is allocated for each calls, something that some of the other solutions avoid. But this is insignificant in almost all cases.
• Only works if you can use Java 8.

Extending the Java8 solution of @skoskav to ReentrantReadWriteLock:

public interface ResourceLock extends AutoCloseable {
    /**
     * Unlocking doesn't throw any checked exception.
     */
    @Override
    void close();
}    

public class CloseableReentrantRWLock extends ReentrantReadWriteLock {

    /**
     * @return an {@link AutoCloseable} once the ReadLock has been acquired
     */
    public ResourceLock lockRead() {
        this.readLock().lock();
        return () -> this.readLock().unlock();
    }

     /**
     * @return an {@link AutoCloseable} once the WriteLock has been acquired.
     */
    public ResourceLock lockWrite() {
        this.writeLock().lock();
        return () -> this.writeLock().unlock();
    }
} 

Here is another solution that works great and is super efficient at the expense of a ThreadLocal lookup per lock request. This solution caches the AutoCloseable part/wrapper and reuses it on a per-thread basis.

First we have a wrapper class ResourceLock around a normal Lock that we will have many instances of. This is the part we want to reuse. The wrapper implements the Lock interface so it behaves like a normal Lock but one that can be auto closed:

public class ResourceLock implements AutoCloseable, Lock {

    private Lock lock;

    public ResourceLock(Lock lock) {
        this(lock, true);
    }
    
    public ResourceLock(Lock lock, boolean eagerLock) {
        this.lock = lock;
        
        if (eagerLock) {
            lock.lock();
        }
    }

    public void lock() {
        lock.lock();
    }

    public void lockInterruptibly() throws InterruptedException {
        lock.lockInterruptibly();
    }

    public Condition newCondition() {
        return lock.newCondition();
    }

    ResourceLock setLock(Lock lock) {
        this.lock = lock;

        return this;
    }

    public boolean tryLock() {
        return lock.tryLock();
    }

    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return lock.tryLock(time, unit);
    }

    public void unlock() {
        lock.unlock();
    }

    @Override
    public void close() {
        lock.unlock();
    }
}

In none reusable form you would simply use it like this:

try (ResourceLock ignore = new ResourceLock(rwl.writeLock())) {
    // Resource locked in here
}

Or we can add a caching capable wrapper which will let us reuse ResourceLock objects per thread.

public class ResourceLockCache {

    private final Lock lock;
    private final Supplier<ResourceLock> cachingStrategy;

    public ResourceLockCache(Lock lock) {
        this.lock = lock;

        final ThreadLocal<ResourceLock> strategy = new ThreadLocal<ResourceLock>() {

            @Override
            protected ResourceLock initialValue() {
                return new ResourceLock();
            }

        };

        this.cachingStrategy = strategy::get;
    }

    public ResourceLockCache(Lock lock, Supplier<ResourceLock> cachingStrategy) {
        this.lock = lock;
        this.cachingStrategy = cachingStrategy;
    }

    public ResourceLock getAsResource() {
        final ResourceLock activeLock = cachingStrategy.get();

        activeLock.setLock(lock);

        return activeLock;
    }

    public ResourceLock getAsResourceAndLock() {
        final ResourceLock activeLock = cachingStrategy.get();

        activeLock.setLock(lock);
        activeLock.lock();

        return activeLock;
    }
}

Now we can use reuse each auto-closeable lock:

ResourceLockCache rlc = new ResourceLockCache(new ReentrantLock());
// Or this to change caching strategy to new object per lock
ResourceLockCache rlc2 = new ResourceLockCache(new ReentrantLock(), ResourceLock::new);

try (ResourceLock ignore = rlc.getAsResourceAndLock()) {
    // Resource locked in here
}

Also have a ReadWriteLock variant for more complex locking needs. It implements the ReadWriteLock interface so its more versatile as you can use complex locking strategies such as tryLock etc:

public class ResourceRWLockCache implements ReadWriteLock {

    private final ReadWriteLock rwl;
    private final Supplier<ResourceLock> cachingStrategy;

    public ResourceRWLockCache(ReadWriteLock rwl) {
        this.rwl = rwl;

        final ThreadLocal<ResourceLock> strategy = new ThreadLocal<ResourceLock>() {

            @Override
            protected ResourceLock initialValue() {
                return new ResourceLock();
            }

        };

        this.cachingStrategy = strategy::get;
    }

    public ResourceRWLockCache(ReadWriteLock rwl, Supplier<ResourceLock> cachingStrategy) {
        this.rwl = rwl;
        this.cachingStrategy = cachingStrategy;
    }

    public ResourceLock readLock() {
        final ResourceLock activeLock = cachingStrategy.get();

        activeLock.setLock(rwl.readLock());

        return activeLock;
    }

    public ResourceLock readLockAndLock() {
        final ResourceLock activeLock = cachingStrategy.get();

        activeLock.setLock(rwl.readLock());
        activeLock.lock();

        return activeLock;
    }

    public ResourceLock writeLock() {
        final ResourceLock activeLock = cachingStrategy.get();

        activeLock.setLock(rwl.writeLock());

        return activeLock;
    }

    public ResourceLock writeLockAndLock() {
        final ResourceLock activeLock = cachingStrategy.get();

        activeLock.setLock(rwl.writeLock());
        activeLock.lock();

        return activeLock;
    }
}

ResourceRWLockCache rwl = new ResourceRWLockCache(new ReentrantReadWriteLock());
// Or this to change caching strategy to new object per lock
ResourceRWLockCache rwl2 = new ResourceRWLockCache(new ReentrantReadWriteLock(), ResourceLock::new);

try (ResourceLock ignore = rwl.writeLockAndLock()) {
    // Resource locked in here
}

Hope this solution helps for single and multi lock strategies with re-using the resource release handlers.

Extending skoskav's excellent answer to ReadWriteLock:

CloseableLock.java:

public interface CloseableLock extends AutoCloseable
{
    /**
     * Release the lock.
     */
    @Override
    void close();
}

ReadWriteLockAsResource:

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;

/**
 * Enables the use of {@code try-with-resources} with {@code ReadWriteLock}.
 */
public final class ReadWriteLockAsResource
{
    private final ReadWriteLock lock;

    /**
     * @param lock a lock
     * @throws NullPointerException if {@code lock} is null
     */
    public ReadWriteLockAsResource(ReadWriteLock lock)
    {
        if (lock == null)
          throw new NullPointerException("lock may not be null");
        this.lock = lock;
    }

    /**
     * Starts a new read-lock.
     *
     * @return the read-lock as a resource
     */
    public CloseableLock readLock()
    {
        Lock readLock = lock.readLock();
        readLock.lock();
        return readLock::unlock;
    }

    /**
     * Starts a new write-lock.
     *
     * @return the write-lock as a resource
     */
    public CloseableLock writeLock()
    {
        Lock writeLock = lock.writeLock();
        writeLock.lock();
        return writeLock::unlock;
    }

    /**
     * Returns a new condition.
     *
     * @return a new condition
     */
    public Condition newCondition()
    {
        return lock.writeLock().newCondition();
    }
}

Usage:

public final class GuideToTheUniverse
{
    private final LockAsResource lock = new LockAsResource(new ReentrantReadWriteLock());
    
    public int answerToLife()
    {
        try (CloseableLock writeLock = lock.writeLock())
        {
            System.out.println("Look ma', no hands!");
            return 42;
        }
    }
}