Netty設計モード-ポリシーモード

ポリシー・モードの特徴は、次のとおりです.
1.一連の代替アルゴリズムファミリーをカプセル化する
2、ある戦略の動的選択をサポートする
 
一般的なポリシー・モードの実装方法

/**
 * @see DefaultEventExecutorChooserFactory#newChooser(EventExecutor[])
 */
public class Strategy {
    private Cache cacheMemory = new CacheMemoryImpl();
    private Cache cacheRedis = new CacheRedisImpl();

    public interface Cache {
        boolean add(String key, Object object);
    }

    public class CacheMemoryImpl implements Cache {
        @Override
        public boolean add(String key, Object object) {
            //    map
            return false;
        }
    }

    public class CacheRedisImpl implements Cache {
        @Override
        public boolean add(String key, Object object) {
            //    redis
            return false;
        }
    }

    public Cache getCache(String key) {
        if (key.length() < 10) {
            return cacheRedis;
        }
        return cacheMemory;
    }
}

nettyのD e f a u l t E v e n t ExecutorChooserFactoryでは、このように戦略モデルを実現しています.

@UnstableApi
public final class DefaultEventExecutorChooserFactory implements EventExecutorChooserFactory {

    public static final DefaultEventExecutorChooserFactory INSTANCE = new DefaultEventExecutorChooserFactory();

    private DefaultEventExecutorChooserFactory() { }

    @SuppressWarnings("unchecked")
    @Override
    public EventExecutorChooser newChooser(EventExecutor[] executors) {
        if (isPowerOfTwo(executors.length)) {
            return new PowerOfTowEventExecutorChooser(executors);
        } else {
            return new GenericEventExecutorChooser(executors);
        }
    }

    private static boolean isPowerOfTwo(int val) {
        return (val & -val) == val;
    }

    private static final class PowerOfTowEventExecutorChooser implements EventExecutorChooser {
        private final AtomicInteger idx = new AtomicInteger();
        private final EventExecutor[] executors;

        PowerOfTowEventExecutorChooser(EventExecutor[] executors) {
            this.executors = executors;
        }

        @Override
        public EventExecutor next() {
            return executors[idx.getAndIncrement() & executors.length - 1];
        }
    }

    private static final class GenericEventExecutorChooser implements EventExecutorChooser {
        private final AtomicInteger idx = new AtomicInteger();
        private final EventExecutor[] executors;

        GenericEventExecutorChooser(EventExecutor[] executors) {
            this.executors = executors;
        }

        @Override
        public EventExecutor next() {
            return executors[Math.abs(idx.getAndIncrement() % executors.length)];
        }
    }
}