Curator源码阅读 - ConnectionState的管理与监听

看看Curator框架 为实现对 连接状态ConnectionState的监听，都是怎么构造框架的。后面我们也可以应用到业务的各种监听中。

Curator2.13实现

接口 Listener

Listener接口，给用户实现stateChange()传入新的状态，用户实现对这新的状态要做什么逻辑处理。

public interface ConnectionStateListener
{
    /**
     * Called when there is a state change in the connection
     * @param client the client
     * @param newState the new state
     */
    public void stateChanged(CuratorFramework client, ConnectionState newState);
}

接口 Listenable

/**
 * Abstracts a listenable object
 */
public interface Listenable
{
    /**
     * Add the given listener. The listener will be executed in the containing instance's thread.
     *
     * @param listener listener to add
     */
    public void     addListener(T listener);

    /**
     * Add the given listener. The listener will be executed using the given
     * executor
     *
     * @param listener listener to add
     * @param executor executor to run listener in
     */
    public void     addListener(T listener, Executor executor);

    public void     removeListener(T listener);
}

抽象类 ListenerContainer implements Listenable

/**
 * Abstracts an object that has listeners 装Listener的容器
 *  Listener类型
 */
public class ListenerContainer implements Listenable
{
    private final Map> listeners = Maps.newConcurrentMap();

    @Override
    public void addListener(T listener)
    {
        addListener(listener, MoreExecutors.sameThreadExecutor());
    }

    @Override
    public void addListener(T listener, Executor executor)
    {
        listeners.put(listener, new ListenerEntry(listener, executor));
    }
    
    /**
     * 对 Listener 列表的遍历进行封装
     * Utility - apply the given function to each listener. 
     * @param function function to call for each listener
     */
    public void forEach(final Function function)
    {
        for ( final ListenerEntry entry : listeners.values() )
        {
            entry.executor.execute
            (
                new Runnable()
                {
                    @Override
                    public void run()
                    {
                        try
                        {
                            function.apply(entry.listener);
                        }
                        catch ( Throwable e )
                        {
                            ThreadUtils.checkInterrupted(e);
                            log.error(String.format("Listener (%s) threw an exception", entry.listener), e);
                        }
                    }
                }
            );
        }
    }
    
    
    public void clear()
    {
        listeners.clear();
    }

    public int size()
    {
        return listeners.size();
    }
    
}

ConnectionStateManager

// to manage connection state
public class ConnectionStateManager {
    // 又是队列？ 玩消息什么的都是用队列。现在是存放 ConnectionState
    BlockingQueue eventQueue = new ArrayBlockingQueue(QUEUE_SIZE);
    // 持有 ListenerContainer
    private final ListenerContainer listeners = new ListenerContainer();
    
    /**
     * Start the manager，起一个线程去执行 processEvents()，要是这线程挂了怎么办？异常怎么处理的？框架怎么处理的。。
     */
    public void start()
    {
        service.submit
            (
                new Callable