Java设计模式之责任链模式的概念、实现以及netty中的责任链模式

public class Request {

 private String name;

 private int days;
 
}

public class Result {

 private boolean agree;

 public Result(boolean agree) {
 this.agree = agree;
 }
}

public interface Handler {
 // 每个处理器持有链，能取到链上的请求或者传递请求
 Result deal(Chain chain);
 
 interface Chain {
 // 获取请求
 Request request();
 // 传递请求
 Result proceed(Request request);
 }
}

public class HandlerChain implements Handler.Chain {
 // 持有链要处理的请求
 private Request request;
 // 持有链上所有的处理器
 private Queue<Handler> handlers;

 public HandlerChain(Request request) {
 this.request = request;
 }
 // 添加一个处理器
 public HandlerChain addHandler(Handler handler) {
 if (handlers == null) {
 handlers = new LinkedList<>();
 }
 handlers.add(handler);
 return this;
 }
 // 实现接口的方法- 获取请求
 public Request request() {
 return request;
 }
 // 实现接口的方法- 处理请求
 public Result proceed(Request request) {
 // 取队首的处理器开始请求。如果队首的处理器处理了，直接返回结果
 // 如果队首的处理器选择传递请求，又会进这个proceed方法。取新的队首处理
 // 为什么是传递而不是直接遍历队列，如果result = null,继续；result != null，返回呢？ 因为传递的方式，可以对request再次处理。A处理器可以做简单处理，再传递给B。
 Handler handler = handlers.poll();
 return handler.deal(this);
 }
}

public class AHandler implements Handler{
 public Result deal(Chain chain) {
 Request request = chain.request();
 // 只处理小于等于1的请求，大于1的请求被传递了
 if (request.getDays() > 1) {
 // 这里可以对request做部分处理，再传递
 return chain.proceed(request);
 }
 System.out.println("A处理了");
 return new Result(true);
 }
} 

public class BHandler implements Handler {
 public Result deal(Chain chain) {
 Request request = chain.request();
 // 只处理小于等于2的请求，大于2的请求被传递了
 if (request.getDays() > 2) {
 return chain.proceed(request);
 }
 System.out.println("B处理了");
 return new Result(true);
 }
}

public class CHandler implements Handler {
 public Result deal(Chain chain) {
 Request request = chain.request();
 // 只处理小于等于3的请求，大于3的请求被传递了
 if (request.getDays() > 3) {
 return chain.proceed(request);
 }
 System.out.println("C处理了");
 return new Result(true);
 }
}

public class Test {

 public static void main(String[] args) {
 // new 一个链，往链上添加处理器
 Request request1 = new Request("hhy", 3);
 HandlerChain chains = new HandlerChain(request1).addHandler(new AHandler()).addHandler(new BHandler()).addHandler(new CHandler());
 Result result1 = chains.proceed(request1);
 System.out.println("结果：" + result1.isAgree());

 }
} 

public static void main(String[] args) {
 EventLoopGroup group = new NioEventLoopGroup();
 NioSocketChannel channel = new NioSocketChannel();
 Bootstrap bootstrap = new Bootstrap();
 bootstrap.group(group).option(ChannelOption.TCP_NODELAY, true);
 InetSocketAddress address = new InetSocketAddress(InetAddress.getByName(httpRequest.host), httpRequest.port);
 group.register(channel);
 channel.connect(address).sync();
 channel.pipeline().addLast("http-decoder", new HttpResponseDecoder());
 channel.pipeline().addLast("http-encoder", new HttpRequestEncoder());
 channel.pipeline().addLast("http-client", new HttpHandler(HttpClient.this));
 channel.writeAndFlush(httpRequest);
}

public class DefaultChannelPipeline implements ChannelPipeline {
 final AbstractChannelHandlerContext head;
 final AbstractChannelHandlerContext tail;

 @Override
 public final ChannelPipeline addLast(EventExecutorGroup group, String name, ChannelHandler handler) {
 final AbstractChannelHandlerContext newCtx;
 synchronized (this) {
 checkMultiplicity(handler);
 // 把handler封装成AbstractChannelHandlerContext
 newCtx = newContext(group, filterName(name, handler), handler);
 // 调用了 addLast0方法
 addLast0(newCtx);
 ...
 }
 callHandlerAdded0(newCtx);
 return this;
 }

 private void addLast0(AbstractChannelHandlerContext newCtx) {
 // 把新加入的处理器设置成尾部的前驱，原尾部的前驱设置成新处理器的后继
 AbstractChannelHandlerContext prev = tail.prev;
 newCtx.prev = prev;
 newCtx.next = tail;
 prev.next = newCtx;
 tail.prev = newCtx;
 }
}

public class DefaultChannelPipeline implements ChannelPipeline {
 ...
 @Override
 public final Channel channel() {
 return channel;
 }

 @Override
 public final ChannelPipeline fireChannelActive() {
 AbstractChannelHandlerContext.invokeChannelActive(head);
 return this;
 }
 ...
}

abstract class AbstractChannelHandlerContext implements ChannelHandlerContext, ResourceLeakHint {
 static void invokeChannelActive(final AbstractChannelHandlerContext next) {
 EventExecutor executor = next.executor();
 if (executor.inEventLoop()) {
  next.invokeChannelActive();
 } else {
  executor.execute(new Runnable() {
  @Override
  public void run() {
   next.invokeChannelActive();
  }
  });
 }
 }
 // 调用了invokeChannelActive
 
 private void invokeChannelActive() {
 // 判断是不是要处理
 if (invokeHandler()) {
  try {
  // 处理
  ((ChannelInboundHandler) handler()).channelActive(this);
  } catch (Throwable t) {
  invokeExceptionCaught(t);
  }
 } else {
  // 事件传递
  fireChannelActive();
 }
 }
 
 @Override
 public ChannelHandlerContext fireChannelActive() {
 // 执行前需要先找到一个合适的处理器 invokeChannelActive
 invokeChannelActive(findContextInbound(MASK_CHANNEL_ACTIVE));
 return this;
 }
 
 private AbstractChannelHandlerContext findContextInbound(int mask) {
 AbstractChannelHandlerContext ctx = this;
 EventExecutor currentExecutor = executor();
 do {
  // 循环，找到一个合适的处理器并返回
  ctx = ctx.next;
 } while (skipContext(ctx, currentExecutor, mask, MASK_ONLY_INBOUND));
 return ctx;
 }
}

public class ChannelInboundHandlerAdapter extends ChannelHandlerAdapter implements ChannelInboundHandler {
 ......
 @Override
 public void channelActive(ChannelHandlerContext ctx) throws Exception {
 ctx.fireChannelActive();
 }
 ......
}