因为ES曾经存在多个版本，次要是每一个版本的启动流程都不一样，我这里不想独自去剖析某一个版本如何进行启动的，解析ES如何去响应HTTP申请的，以及背地如何去实现。上面简略给大家剖析下，HTTP服务器实现。
HTTP Server
Elasticsearch Netty注册服务器 Netty4HttpServerTransport
protected void doStart() { boolean success = false; try { serverBootstrap = new ServerBootstrap(); serverBootstrap.group(new NioEventLoopGroup(workerCount, daemonThreadFactory(settings, HTTP_SERVER_WORKER_THREAD_NAME_PREFIX))); // NettyAllocator will return the channel type designed to work with the configuredAllocator serverBootstrap.channel(NettyAllocator.getServerChannelType()); // Set the allocators for both the server channel and the child channels created serverBootstrap.option(ChannelOption.ALLOCATOR, NettyAllocator.getAllocator()); serverBootstrap.childOption(ChannelOption.ALLOCATOR, NettyAllocator.getAllocator()); serverBootstrap.childHandler(configureServerChannelHandler()); serverBootstrap.handler(new ServerChannelExceptionHandler(this)); serverBootstrap.childOption(ChannelOption.TCP_NODELAY, SETTING_HTTP_TCP_NO_DELAY.get(settings)); serverBootstrap.childOption(ChannelOption.SO_KEEPALIVE, SETTING_HTTP_TCP_KEEP_ALIVE.get(settings)); // 省略局部代码 final ByteSizeValue tcpSendBufferSize = SETTING_HTTP_TCP_SEND_BUFFER_SIZE.get(settings); if (tcpSendBufferSize.getBytes() > 0) { serverBootstrap.childOption(ChannelOption.SO_SNDBUF, Math.toIntExact(tcpSendBufferSize.getBytes())); } final ByteSizeValue tcpReceiveBufferSize = SETTING_HTTP_TCP_RECEIVE_BUFFER_SIZE.get(settings); if (tcpReceiveBufferSize.getBytes() > 0) { serverBootstrap.childOption(ChannelOption.SO_RCVBUF, Math.toIntExact(tcpReceiveBufferSize.getBytes())); } serverBootstrap.option(ChannelOption.RCVBUF_ALLOCATOR, recvByteBufAllocator); serverBootstrap.childOption(ChannelOption.RCVBUF_ALLOCATOR, recvByteBufAllocator); final boolean reuseAddress = SETTING_HTTP_TCP_REUSE_ADDRESS.get(settings); serverBootstrap.option(ChannelOption.SO_REUSEADDR, reuseAddress); serverBootstrap.childOption(ChannelOption.SO_REUSEADDR, reuseAddress); // 绑定端口和地址 bindServer(); success = true; } finally { if (success == false) { doStop(); // otherwise we leak threads since we never moved to started } } }用过Netty晓得下面代码什么意思，设置worker线程,TCP设置，设置管道handler。Netty的连贯进去个别都是在childHandler()设置ChannelInitializer 实现类中增加，看下configureServerChannelHandler()次要初始化了HttpChannelHandler，在initChannel()能看到增加了那个处理器。
protected void initChannel(Channel ch) throws Exception { Netty4HttpChannel nettyHttpChannel = new Netty4HttpChannel(ch); ch.attr(HTTP_CHANNEL_KEY).set(nettyHttpChannel); ch.pipeline().addLast("read_timeout", new ReadTimeoutHandler(transport.readTimeoutMillis, TimeUnit.MILLISECONDS)); final HttpRequestDecoder decoder = new HttpRequestDecoder( handlingSettings.getMaxInitialLineLength(), handlingSettings.getMaxHeaderSize(), handlingSettings.getMaxChunkSize()); decoder.setCumulator(ByteToMessageDecoder.COMPOSITE_CUMULATOR); ch.pipeline().addLast("decoder", decoder); ch.pipeline().addLast("decoder_compress", new HttpContentDecompressor()); ch.pipeline().addLast("encoder", new HttpResponseEncoder()); final HttpObjectAggregator aggregator = new HttpObjectAggregator(handlingSettings.getMaxContentLength()); aggregator.setMaxCumulationBufferComponents(transport.maxCompositeBufferComponents); ch.pipeline().addLast("aggregator", aggregator); if (handlingSettings.isCompression()) { ch.pipeline().addLast("encoder_compress", new HttpContentCompressor(handlingSettings.getCompressionLevel())); } if (handlingSettings.isCorsEnabled()) { ch.pipeline().addLast("cors", new Netty4CorsHandler(transport.corsConfig)); } ch.pipeline().addLast("pipelining", new Netty4HttpPipeliningHandler(logger, transport.pipeliningMaxEvents)); ch.pipeline().addLast("handler", requestHandler); transport.serverAcceptedChannel(nettyHttpChannel); }从下面代码晓得解决申请的是： requestHandler，它的实现类： Netty4HttpRequestHandler
protected void channelRead0(ChannelHandlerContext ctx, HttpPipelinedRequest<FullHttpRequest> msg) { Netty4HttpChannel channel = ctx.channel().attr(Netty4HttpServerTransport.HTTP_CHANNEL_KEY).get(); FullHttpRequest request = msg.getRequest(); boolean success = false; Netty4HttpRequest httpRequest = new Netty4HttpRequest(request, msg.getSequence()); try { if (request.decoderResult().isFailure()) { Throwable cause = request.decoderResult().cause(); if (cause instanceof Error) { ExceptionsHelper.maybeDieOnAnotherThread(cause); serverTransport.incomingRequestError(httpRequest, channel, new Exception(cause)); } else { serverTransport.incomingRequestError(httpRequest, channel, (Exception) cause); } } else { serverTransport.incomingRequest(httpRequest, channel); } success = true; } finally { if (success == false) { httpRequest.release(); }能够看出解决http申请的办法，委派了Netty4HttpServerTransport，也就是下面进行Netty server的类。这里的逻辑将httpRequest,channel 转换成Elasticsearch 模板对象，屏蔽掉底层api，再从线程池中获取ThreadContext进行工作执行。相似一个http散发器。具体代码就不展现进去，一连串的办法调用，看下图
TransportAction.doExecute是一个形象办法，由NodeClient.transportAction返回的实现类去调用执行。每一个URL都会有对应的transportAction实现类，这个和咱们平时MVC架构不一样。NodeClient内置了Map<ActionType, TransportAction> actions，外面蕴含所有HTTP申请解决办法，有300多个值对应不同场景的解决。
看下最简略的响应，当我申请ES:9200端口时，返回根底信息,由TransportMainAction如何响应的
public class TransportMainAction extends HandledTransportAction<MainRequest, MainResponse> { private final String nodeName; private final ClusterService clusterService; @Inject public TransportMainAction(Settings settings, TransportService transportService, ActionFilters actionFilters, ClusterService clusterService) { super(MainAction.NAME, transportService, actionFilters, MainRequest::new); this.nodeName = Node.NODE_NAME_SETTING.get(settings); this.clusterService = clusterService; } @Override protected void doExecute(Task task, MainRequest request, ActionListener<MainResponse> listener) { ClusterState clusterState = clusterService.state(); listener.onResponse( new MainResponse(nodeName, Version.CURRENT, clusterState.getClusterName(), clusterState.metaData().clusterUUID(), Build.CURRENT)); }}总结
剖析这么多代码， ES解决HTTP申请链尽管是执行过程比拟绕，然而理论代码还是比较简单，整体还是去剖析TransportAction.doExecute如何响应申请的。