@Forward

An annotation processor for generating forwarders.

Grab the latest release from Maven Central

Use

To create the equivalent of Guava's 100+ line ForwardingDeque you could write the following:

import java.util.Deque;
import uno.perk.forward.Forward;

/**
 * A deque which forwards all its method calls to another deque. Subclasses
 * should override one or more methods to modify the behavior of the backing
 * deque as desired per the <a
 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p><b>Warning:</b> The methods of {@code ForwardingDeque} forward
 * <b>indiscriminately</b> to the methods of the delegate. For example,
 * overriding {@link #add} alone <b>will not</b> change the behavior of {@link
 * #offer} which can lead to unexpected behavior. In this case, you should
 * override {@code offer} as well.
 */
@Forward(Deque.class)
public abstract class ForwardingDeque<E> extends ForwardingDequeForwarder<E> {
  public ForwardingDeque(Deque<E> deque) {
    super(deque);
  }
}

The @Forward annotation will be processed and code will be generated for ForwardingDequeForwarder which does all the work of forwarding all the Deque methods through the supplied deque delegate.

Alternatively, instead of generating a ForwardingDeque and extending it to add decoration, you can just create an ad-hoc forwarder for immediate local use:

@Forward(Deque.class)
public class InstrumentedDeque<E> extends InstrumentedDequeForwarder<E> {
  private long addFirstCalls;
  
  public InstrumentedDeque(Deque<E> deque) {
    super(deque);
  }
  
  @Override
  public void addFirst(E e) {
    addFirstCalls++;
    deque.addFirst(e);
  }
  
  public long getAddFirstCallCount() {
    return addFirstCalls;
  }
}

NB: The delegate field is exposed as a protected final field with the lower-camel-case name of its type.

Features

• More than one type can be forwarded.
• The name of the generated forwarder class can be customised via @Forward's forwarderPattern.

Known Limitations

• Only interface types can be forwarded.

Requirements

• Java 8

Development

Pull requests are welcome.

We use Travis CI to verify the build .

Acknowledgements

Special thanks to the folks at Square for javapoet - a wonderful tool for writing code-generating annotation processors.