Tomcat处理请求流程

1. Connector组件的Acceptor监听客户端套接字连接并接收Socket。
2. 将连接交给线程池Executor处理，开始执行请求响应任务。
3. Processor组件读取消息报文，解析请求行、请求体、请求头，封装成Request对象。
4. Mapper组件根据请求行的URL值和请求头的Host值匹配由哪个Host容器、Context容器、Wrapper容器处理请求。
5. CoyoteAdaptor组件负责将Connector组件和Engine容器关联起来，把生成的Request对象和响应对象Response传递到Engine容器中，调用 Pipeline。
6. Engine容器的管道开始处理，管道中包含若干个Valve、每个Valve负责部分处理逻辑。执行完Valve后会执行基础的 Valve--StandardEngineValve，负责调用Host容器的Pipeline。
7. Host容器的管道开始处理，流程类似，最后执行 Context容器的Pipeline。
8. Context容器的管道开始处理，流程类似，最后执行 Wrapper容器的Pipeline。
9. Wrapper容器的管道开始处理，流程类似，最后执行 Wrapper容器对应的Servlet对象的 处理方法

Connector

<Connector port="8080" protocol="HTTP/1.1"
               connectionTimeout="20000"
               redirectPort="8443" />
<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />

​ Connector用于接收请求并将请求封装成Request和Response来具体处理。最底层使用的是 Socket。Request和Response封装后交给Container（Servlet的容器）处理请求，Container处理后返回给Connector，最后由Socket返回给客户端。

结构

​ Connector中具体是用 ProtocolHandler处理请求的，代表不同的连接类型。Http11Protocol使用普通Socket连接，Http11NioProtocol使用NioSocket连接。

​ ProtocolHandler中有三个重要的组件：

• Endpoint：处理底层的Socket网络连接；
• Processor：将Endpoint接收的Socket封装成Request；
• Adapter：将封装后的Request交给Container处理；

​ Endpoint的抽象类 AbstractEndpoint定义了 Acceptor和 AsyncTimeout两个内部类 和 Handler接口。

• Acceptor：监听请求；
• AsyncTimeout：检查异步Request请求的超时；
• Handler：处理接收的Socket，内部调用 Processor进行处理；

public class Connector extends LifecycleMBeanBase  {
    public Connector() { this(null); }
    public Connector(String protocol) {
        // 根据 server.xml 中 Connector 属性 protocol 的值找合适的 className
        // 此处返回  org.apache.coyote.http11.Http11NioProtocol
        // 赋值给  ProtocolHandler
        setProtocol(protocol);
        ProtocolHandler p = null;
        try {
            Class<?> clazz = Class.forName(protocolHandlerClassName);
            // 反射生成 Http11NioProtocol 时，在构造函数中 生成了 NioEndpoint。
            p = (ProtocolHandler) clazz.getConstructor().newInstance();
        } finally {
            this.protocolHandler = p;
        }
        // 设置编码集
        if (Globals.STRICT_SERVLET_COMPLIANCE) {
            uriCharset = StandardCharsets.ISO_8859_1;
        } else {
            uriCharset = StandardCharsets.UTF_8;
        }
    }
    // 初始化操作
    @Override
    protected void initInternal() throws LifecycleException {
        super.initInternal();
        // 初始化是配置  CoyoteAdapter(Connector 作为参数)
        adapter = new CoyoteAdapter(this);
        // 协议处理器绑定 适配器
        protocolHandler.setAdapter(adapter);
        // 执行 协议处理器初始化操作
        protocolHandler.init();
    }
    // 使用此 连接器处理 请求
    @Override
    protected void startInternal() {
        // 验证端口
        if (getPort() < 0) { }
        // 设置生命周期状态值
        setState(LifecycleState.STARTING);
        // 调用 协议处理器 start 方法 
        protocolHandler.start();
    }
}

Http11NioProtocol

​ 主要包含 NioEndpoint组件和 Http11NioProcessor组件。启动时由NioEndpoint组件启动端口监听，连接到来被注册到NioChannel队列中，由Poller轮询器负责检测Channel的读写事件，并在创建任务后放入线程池中，线程池进行任务处理。

public class Http11NioProtocol extends AbstractHttp11JsseProtocol<NioChannel> {
    // 创建了  NioEndpoint 类
    public Http11NioProtocol() {
        // 最终调用 AbstractProtocol 类
        super(new NioEndpoint());
    }
}

// 父类 AbstractProtocol
public abstract class AbstractProtocol implements ProtocolHandler,MBeanRegistration {
    @Override
    public void init() throws Exception {
        // endpointName---"http-nio-8080": http-nio  +  8080 组成。
        String endpointName = getName();
        // 去掉 双引号
        endpoint.setName(endpointName.substring(1, endpointName.length()-1));
        // domain ==  catalina
        endpoint.setDomain(domain);
        // Endpoint的初始化操作
        // serverSocketChannel 绑定端口
        endpoint.init();
    }
    @Override
    public void start() throws Exception {
        // Endpoint 的 start 方法，重点
        // 创建 Executor、最大连接、开启 Poller thread
        endpoint.start();
        // 异步超时 线程，
        asyncTimeout = new AsyncTimeout();
        Thread timeoutThread = new Thread(asyncTimeout, getNameInternal() + "-AsyncTimeout");
        int priority = endpoint.getThreadPriority();
        if (priority < Thread.MIN_PRIORITY || priority > Thread.MAX_PRIORITY) {
            priority = Thread.NORM_PRIORITY;
        }
        timeoutThread.setPriority(priority);
        timeoutThread.setDaemon(true);
        timeoutThread.start();
    }
}

// AsyncTimeout 实现 Runnable 接口
protected class AsyncTimeout implements Runnable {
    private volatile boolean asyncTimeoutRunning = true;
    // 后台线程检查异步请求并在没有活动时触发超时。
    @Override
    public void run() {
        // 死循环，直到接收到 shutdown 命令
        while (asyncTimeoutRunning) {
            Thread.sleep(1000);
            long now = System.currentTimeMillis();
            for (Processor processor : waitingProcessors) {
                processor.timeoutAsync(now);
            }
            // 循环，直到 Endpoint pause
            while (endpoint.isPaused() && asyncTimeoutRunning) {
                Thread.sleep(1000);
            }
        }
    }
}

NioEndpoint

​ NioEndpoint是非阻塞IO的一个抽象，包含了：

• LimitLatch：连接数控制器。
• Acceptor：套接字连接并注册到Channel队列中。
• Poller：轮询检查事件列表。
• SocketProcessor：任务定义器。
• Executor：负责处理套接字。

// AbstractEndpoint
public void init() throws Exception {
    if (bindOnInit) {
        bind();
        bindState = BindState.BOUND_ON_INIT;
    }
}
public final void start() throws Exception {
    // 判断是否绑定过
    if (bindState == BindState.UNBOUND) {
        bind();
        bindState = BindState.BOUND_ON_START;
    }
    startInternal();
}

// NioEndpoint
@Override
public void bind() throws Exception {
	// 绑定 设置的端口
    if (!getUseInheritedChannel()) {
        serverSock = ServerSocketChannel.open();
        socketProperties.setProperties(serverSock.socket());
        InetSocketAddress addr = (getAddress()!=null?new InetSocketAddress(getAddress(),getPort()):new InetSocketAddress(getPort()));
        serverSock.socket().bind(addr,getAcceptCount());
    } else {
        // Retrieve the channel provided by the OS
        Channel ic = System.inheritedChannel();
        if (ic instanceof ServerSocketChannel) {
            serverSock = (ServerSocketChannel) ic;
        }
    }
    // 设置 阻塞模式
    serverSock.configureBlocking(true); //mimic APR behavior
    // 初始化 连接器、轮询器 默认线程数
    if (acceptorThreadCount == 0) {
        acceptorThreadCount = 1;
    }
    if (pollerThreadCount <= 0) {
        pollerThreadCount = 1;
    }
    setStopLatch(new CountDownLatch(pollerThreadCount));
    // 是否初始化 ssl
    initialiseSsl();
    selectorPool.open();
}

// 开启 NIO endpoint, 创建 acceptor, poller 线程.
@Override
public void startInternal() throws Exception {
	// 设置 running 状态
    if (!running) {
        running = true;
        paused = false;
        // 默认 DEFAULT_SIZE：128  500
        processorCache = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                                                 socketProperties.getProcessorCache());
        eventCache = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                                             socketProperties.getEventCache());
        nioChannels = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                                              socketProperties.getBufferPool());
        if ( getExecutor() == null ) {
            createExecutor();
        }
		// 初始化 连接数控制器，默认最大连接数 10000
        initializeConnectionLatch();
        // 开启 poller 线程， 默认 2
        // 检测到 事件后，交给 processor 处理
        pollers = new Poller[getPollerThreadCount()];
        for (int i=0; i<pollers.length; i++) {
            pollers[i] = new Poller();
            Thread pollerThread = new Thread(pollers[i], 
                                             getName() + "-ClientPoller-"+i);
            pollerThread.setPriority(threadPriority);
            pollerThread.setDaemon(true);
            pollerThread.start();
        }
        // 开启 Acceptor 线程
        startAcceptorThreads();
    }
}
// AbstractEndpoint
protected final void startAcceptorThreads() {
    int count = getAcceptorThreadCount();
    acceptors = new Acceptor[count];
    // 开启 Acceptor 线程
    for (int i = 0; i < count; i++) {
        // NioEndpoint 中实现
        acceptors[i] = createAcceptor();
        String threadName = getName() + "-Acceptor-" + i;
        acceptors[i].setThreadName(threadName);
        Thread t = new Thread(acceptors[i], threadName);
        t.setPriority(getAcceptorThreadPriority());
        t.setDaemon(getDaemon());
        t.start();
    }
}

连接数控制器-------LimitLatch

处理流程图：

​ NIO模式下，Tomcat默认把阀门大小设置为 10000，可在 server.xml Connector节点下配置 maxConnections 属性修改。在连接数到达最大值后，仍可以接收客户端连接，直到操作系统接收队列被塞满。默认100，可在 Connector节点下 配置 acceptCount 属性修改。

SocketChannel接收器--------Acceptor

​ Acceptor主要监听是否有客户端发来的连接并接收该连接，accept操作是阻塞的。此时返回 SocketChannel对象。Acceptor接收 SocketChannel 对象后要把它设置成非阻塞（后面对客户端连接才去非阻塞模式处理），接着设置套接字属性，封装成非阻塞通道对象。（NioChannel--HTTP、SecureNioChannel--HTTPS），最后将非阻塞通道对象注册到通道队列由 Poller 负责检测事件。

// NioEndpoint
protected class Acceptor extends AbstractEndpoint.Acceptor {
    @Override
    public void run() {
        int errorDelay = 0;
        // 死循环，知道收到  shutdown 命令
        while (running) {
            // Loop if endpoint is paused
            while (paused && running) {
                state = AcceptorState.PAUSED;
                Thread.sleep(50);
            }
            if (!running) {
                break;
            }
            state = AcceptorState.RUNNING;
            try {
                // 超过最大 连接，等待状态
                countUpOrAwaitConnection();
                // 接收从server来的下一个socket连接
                SocketChannel socket = serverSock.accept();
                // 正确接收 socket，重置 errorDelay
                errorDelay = 0;
                // Configure the socket
                if (running && !paused) {
                    // 把 socket 交给合适的 处理器处理
                    if (!setSocketOptions(socket)) {
                        closeSocket(socket);
                    }
                } else {
                    closeSocket(socket);
                }
            }
        }
        state = AcceptorState.ENDED;
    }
}
protected boolean setSocketOptions(SocketChannel socket) {
    // 处理 socket
    try {
        // 设置 非阻塞模式
        socket.configureBlocking(false);
        Socket sock = socket.socket();
        socketProperties.setProperties(sock);
        NioChannel channel = nioChannels.pop();
        if (channel == null) {
            SocketBufferHandler bufhandler = new SocketBufferHandler(
                socketProperties.getAppReadBufSize(),
                socketProperties.getAppWriteBufSize(),
                socketProperties.getDirectBuffer());
            // 判断是否开启 SSL 类型，生成不同类型的 Channel
            if (isSSLEnabled()) {
                channel = new SecureNioChannel(socket, bufhandler, selectorPool, this);
            } else {
                channel = new NioChannel(socket, bufhandler);
            }
        } else {
            channel.setIOChannel(socket);
            channel.reset();
        }
        // 获取 Poller，注册 成 Event 事件。
        getPoller0().register(channel);
    } catch (Throwable t) {
        // 出错了，就返回，进行 关闭 socket 处理
        return false;
    }
    return true;
}

轮询器----Poller

​ 需要同时对很多连接进行管理，通过不断遍历事件列表，对对应连接的相应事件作出处理。Poller内部依赖 JDK的Selector对象进行轮询，Selector会选择出待处理的事件，每轮询一次就选出若干需要处理的NioChannel，在NIO模式下，每次读取的数据时不确定的，每次读取的数据可能有请求头和请求行，每次只能尝试去解析报文，如果解析不成功则等待下次轮询读取更多数据后再次尝试，如果解析成功则做一些逻辑处理后对客户端响应，这些处理工作在任务定义器中定义。

// 在 NioEndpoint startInternal方法中
pollers = new Poller[getPollerThreadCount()];
for (int i=0; i<pollers.length; i++) {
    pollers[i] = new Poller();
    Thread pollerThread = new Thread(pollers[i], getName() + "-ClientPoller-"+i);
    pollerThread.setPriority(threadPriority);
    pollerThread.setDaemon(true);
    pollerThread.start();
}

// NioEndpoint 类中定义
public class Poller implements Runnable {
    private final SynchronizedQueue<PollerEvent> events =
        new SynchronizedQueue<>();
    private volatile boolean close = false;
    private Selector selector;
    @Override
    public void run() {
        // 死循环，直到调用 destory 法
        while (true) {
            boolean hasEvents = false;
            try {
                if (!close) {
                    // 在 Acceptor 收到请求封装成 Socket 注册到 event 中
                    // 在轮询时从Event中取，进行处理
                    hasEvents = events();
                    if (wakeupCounter.getAndSet(-1) > 0) {
                        //if we are here, means we have other stuff to do
                        //do a non blocking select
                        keyCount = selector.selectNow();
                    } else {
                        keyCount = selector.select(selectorTimeout);
                    }
                    wakeupCounter.set(0);
                }
                if (close) {
                    events();
                    timeout(0, false);
                    try {
                        selector.close();
                    } catch (IOException ioe) {
                        log.error(sm.getString("endpoint.nio.selectorCloseFail"), ioe);
                    }
                    break;
                }
            } catch (Throwable x) {
                continue;
            }
            //either we timed out or we woke up, process events first
            if ( keyCount == 0 ) hasEvents = (hasEvents | events());

            Iterator<SelectionKey> iterator =
                keyCount > 0 ? selector.selectedKeys().iterator() : null;
            // Walk through the collection of ready keys and dispatch
            // any active event.
            while (iterator != null && iterator.hasNext()) {
                SelectionKey sk = iterator.next();
                NioSocketWrapper attachment = (NioSocketWrapper)sk.attachment();
                // 另一个线程调用了 cancelledKey 方法，attachment 可能为null
                // 移除次事件，否则进行处理事件
                if (attachment == null) {
                    iterator.remove();
                } else {
                    iterator.remove();
                    processKey(sk, attachment);
                }
            }
            // 处理超时情况
            timeout(keyCount,hasEvents);
        }
        getStopLatch().countDown();
    }

    protected void processKey(SelectionKey sk, NioSocketWrapper attachment) {
        try {
            if ( close ) {
                cancelledKey(sk);
            } else if ( sk.isValid() && attachment != null ) {
                if (sk.isReadable() || sk.isWritable() ) {
                    if ( attachment.getSendfileData() != null ) {
                        processSendfile(sk,attachment, false);
                    } else {
                        unreg(sk, attachment, sk.readyOps());
                        boolean closeSocket = false;
                        // Read goes before write
                        if (sk.isReadable()) {
                            // 在父类中定义
                            if (!processSocket(attachment, SocketEvent.OPEN_READ, true)) {
                                closeSocket = true;
                            }
                        }
                        if (!closeSocket && sk.isWritable()) {
                            if (!processSocket(attachment, SocketEvent.OPEN_WRITE, true)) {
                                closeSocket = true;
                            }
                        }
                        if (closeSocket) {
                            cancelledKey(sk);
                        }
                    }
                }
            } else {
                //invalid key
                cancelledKey(sk);
            }
        } catch ( CancelledKeyException ckx ) {
            cancelledKey(sk);
        }
    }
}
// AbstractEndpoint
public boolean processSocket(SocketWrapperBase<S> socketWrapper,
                             SocketEvent event, boolean dispatch) {
    try {
        if (socketWrapper == null) {
            return false;
        }
        // 从 栈中取一个
        SocketProcessorBase<S> sc = processorCache.pop();
        if (sc == null) {
   			// 没有就新建一个
            sc = createSocketProcessor(socketWrapper, event);
        } else {
            sc.reset(socketWrapper, event);
        }
        // 判断是否有 Executor，最终都是调用 Processor 的 run方法。
        Executor executor = getExecutor();
        // 见SocketProcessor
        if (dispatch && executor != null) {
            executor.execute(sc);
        } else {
            sc.run();
        }
    } catch (RejectedExecutionException ree) {
        return false;
    }
    return true;
}

任务定义器---SocketProcessor

// 在上面的操作中，执行 run 方法时，
// SocketProcessorBase
@Override
public final void run() {
    synchronized (socketWrapper) {
        if (socketWrapper.isClosed()) {
            return;
        }
        doRun();
    }
}
// 在 NioEndpoint 类中实现
@Override
protected void doRun() {
    NioChannel socket = socketWrapper.getSocket();
    SelectionKey key = socket.getIOChannel().keyFor(socket.getPoller().getSelector());
    int handshake = -1;
    if (handshake == 0) {
        SocketState state = SocketState.OPEN;
        // 处理请求
        if (event == null) {
            // 调用 Handler 转交给 Processor 去处理 process 方法，
            state = getHandler().process(socketWrapper, SocketEvent.OPEN_READ);
        } else {
            state = getHandler().process(socketWrapper, event);
        }
        if (state == SocketState.CLOSED) {
            close(socket, key);
        }
    }
    socketWrapper = null;
    event = null;
    //return to cache
    if (running && !paused) {
        processorCache.push(this);
    }
}

// AbstractProtocol
protected static class ConnectionHandler<S> implements AbstractEndpoint.Handler<S> {
    @Override
    public SocketState process(SocketWrapperBase<S> wrapper, SocketEvent status) {
        if (wrapper == null) {
            return SocketState.CLOSED;
        }
        S socket = wrapper.getSocket();
        // 根据Socket获取具体协议的处理器
        Processor processor = connections.get(socket);
        // 如果process==null，尝试其它协议、新建等
        // SSL 支持
        processor.setSslSupport(
            wrapper.getSslSupport(getProtocol().getClientCertProvider()));
        // process 和 connection 关联
        connections.put(socket, processor);
        SocketState state = SocketState.CLOSED;
        do {
            // 处理
            state = processor.process(wrapper, status);
        } while ( state == SocketState.UPGRADING);
        // Make sure socket/processor is removed from the list of current
        connections.remove(socket);
        release(processor);
        return SocketState.CLOSED;
    }
}

// AbstractProcessorLight(公共父类)
@Override
public SocketState process(SocketWrapperBase<?> socketWrapper, SocketEvent status)
    throws IOException {
    SocketState state = SocketState.CLOSED;
    Iterator<DispatchType> dispatches = null;
    do {
        // 根据 SocketEvent 所处的 状态执行不同操作。
        if (dispatches != null) {
            DispatchType nextDispatch = dispatches.next();
            state = dispatch(nextDispatch.getSocketStatus());
        } else if (status == SocketEvent.DISCONNECT) {
            // Do nothing here, just wait for it to get recycled
        } else if (isAsync() || isUpgrade() || state == SocketState.ASYNC_END) {
            state = dispatch(status);
            if (state == SocketState.OPEN) {
                state = service(socketWrapper);
            }
        } else if (status == SocketEvent.OPEN_WRITE) {
            state = SocketState.LONG;
        } else if (status == SocketEvent.OPEN_READ){
            state = service(socketWrapper);
        } else {
            state = SocketState.CLOSED;
        }
        if (state != SocketState.CLOSED && isAsync()) {
            state = asyncPostProcess();
        }
        if (dispatches == null || !dispatches.hasNext()) {
            dispatches = getIteratorAndClearDispatches();
        }
    } while (state == SocketState.ASYNC_END ||
             dispatches != null && state != SocketState.CLOSED);
    return state;
}

// 调用具体协议的service方法处理请求
@Override
public SocketState service(SocketWrapperBase<?> socketWrapper) {
    // 判断状态
    while (!getErrorState().isError() && keepAlive && !isAsync() 
           && upgradeToken == null &&
           sendfileState == SendfileState.DONE && !endpoint.isPaused()) {

        // 解析request请求头
        try {
            if (!inputBuffer.parseRequestLine(keptAlive)) {
                if (inputBuffer.getParsingRequestLinePhase() == -1) {
                    return SocketState.UPGRADING;
                } else if (handleIncompleteRequestLineRead()) {
                    break;
                }
            }
            if (endpoint.isPaused()) {
                response.setStatus(503);
                setErrorState(ErrorState.CLOSE_CLEAN, null);
            } else {
                keptAlive = true;
                request.getMimeHeaders().setLimit(endpoint.getMaxHeaderCount());
                if (!inputBuffer.parseHeaders()) {
                    openSocket = true;
                    readComplete = false;
                    break;
                }
                if (!disableUploadTimeout) {
                    socketWrapper.setReadTimeout(connectionUploadTimeout);
                }
            }
        } catch (IOException e) {
            setErrorState(ErrorState.CLOSE_CONNECTION_NOW, e); break;
        } catch (Throwable t) {
            // 400 - Bad Request
            response.setStatus(400);
            setErrorState(ErrorState.CLOSE_CLEAN, t);
            // 日志调用处
            getAdapter().log(request, response, 0);
        }
        // Has an upgrade been requested?
        Enumeration<String> connectionValues = request.getMimeHeaders().values("Connection");
        boolean foundUpgrade = false;
        while (connectionValues.hasMoreElements() && !foundUpgrade) {
            foundUpgrade = connectionValues.nextElement().toLowerCase(
                Locale.ENGLISH).contains("upgrade");
        }
        if (foundUpgrade) {
            // Check the protocol
            String requestedProtocol = request.getHeader("Upgrade");
            UpgradeProtocol upgradeProtocol = httpUpgradeProtocols.get(requestedProtocol);
            if (upgradeProtocol != null) {
                if (upgradeProtocol.accept(request)) {
                    response.setStatus(HttpServletResponse.SC_SWITCHING_PROTOCOLS);
                    response.setHeader("Connection", "Upgrade");
                    response.setHeader("Upgrade", requestedProtocol);
                    action(ActionCode.CLOSE,  null);
                    getAdapter().log(request, response, 0);

                    InternalHttpUpgradeHandler upgradeHandler =
                        upgradeProtocol.getInternalUpgradeHandler(
                        getAdapter(), cloneRequest(request));
                    UpgradeToken upgradeToken = new UpgradeToken(upgradeHandler, null, null);
                    action(ActionCode.UPGRADE, upgradeToken);
                    return SocketState.UPGRADING;
                }
            }
        }

        if (!getErrorState().isError()) {
            rp.setStage(org.apache.coyote.Constants.STAGE_PREPARE);
            try {
                prepareRequest();
            } catch (Throwable t) {
                // 500 - Internal Server Error
                response.setStatus(500);
                setErrorState(ErrorState.CLOSE_CLEAN, t);
                getAdapter().log(request, response, 0);
            }
        }

        if (maxKeepAliveRequests == 1) {
            keepAlive = false;
        } else if (maxKeepAliveRequests > 0 &&
                   socketWrapper.decrementKeepAlive() <= 0) {
            keepAlive = false;
        }

        // 通过 CoyotAdapte 处理 request
        if (!getErrorState().isError()) {
            try {
                rp.setStage(org.apache.coyote.Constants.STAGE_SERVICE);
                // 处理 request，见 CoyoteAdapter 解析
                getAdapter().service(request, response);
                if(keepAlive && !getErrorState().isError() && !isAsync() &&
                   statusDropsConnection(response.getStatus())) {
                    setErrorState(ErrorState.CLOSE_CLEAN, null);
                }
            } catch (InterruptedIOException e) {
                setErrorState(ErrorState.CLOSE_CONNECTION_NOW, e);
            } catch (HeadersTooLargeException e) {
                if (response.isCommitted()) {
                    setErrorState(ErrorState.CLOSE_NOW, e);
                } else {
                    response.reset();
                    response.setStatus(500);
                    setErrorState(ErrorState.CLOSE_CLEAN, e);
                    response.setHeader("Connection", "close");
                }
            } catch (Throwable t) {
                // 500 - Internal Server Error
                response.setStatus(500);
                setErrorState(ErrorState.CLOSE_CLEAN, t);
                getAdapter().log(request, response, 0);
            }
        }

        // Finish the handling of the request
        rp.setStage(org.apache.coyote.Constants.STAGE_ENDINPUT);
        if (!isAsync()) {
            endRequest();
        }
        rp.setStage(org.apache.coyote.Constants.STAGE_ENDOUTPUT);

        // If there was an error, make sure the request is counted as
        // and error, and update the statistics counter
        if (getErrorState().isError()) {
            response.setStatus(500);
        }

        if (!isAsync() || getErrorState().isError()) {
            request.updateCounters();
            if (getErrorState().isIoAllowed()) {
                inputBuffer.nextRequest();
                outputBuffer.nextRequest();
            }
        }
        if (!disableUploadTimeout) {
            int soTimeout = endpoint.getConnectionTimeout();
            if(soTimeout > 0) {
                socketWrapper.setReadTimeout(soTimeout);
            } else {
                socketWrapper.setReadTimeout(0);
            }
        }
        rp.setStage(org.apache.coyote.Constants.STAGE_KEEPALIVE);
        sendfileState = processSendfile(socketWrapper);
    }
    rp.setStage(org.apache.coyote.Constants.STAGE_ENDED);
}

CoyoteAdapter

@Override
public void service(org.apache.coyote.Request req, org.apache.coyote.Response res) {
    Request request = (Request) req.getNote(ADAPTER_NOTES);
    Response response = (Response) res.getNote(ADAPTER_NOTES);
	// request == null，新建并关联
    if (request == null) {
        // Create objects
        request = connector.createRequest();
        request.setCoyoteRequest(req);
        response = connector.createResponse();
        response.setCoyoteResponse(res);
        // Link objects
        request.setResponse(response);
        response.setRequest(request);
        // Set as notes
        req.setNote(ADAPTER_NOTES, request);
        res.setNote(ADAPTER_NOTES, response);
        // Set query string encoding
        req.getParameters().setQueryStringCharset(connector.getURICharset());
    }
	// 设置请求头，告知网站是用何种语言或框架编写的
    // 默认false，Servlet/4.0 JSP/2.3xxxxxxxxxxxxxx
    if (connector.getXpoweredBy()) {
        response.addHeader("X-Powered-By", POWERED_BY);
    }
    boolean async = false;
    boolean postParseSuccess = false;
    req.getRequestProcessor().setWorkerThreadName(THREAD_NAME.get());
    try {
        // 请求映射、解析参数等操作。
        postParseSuccess = postParseRequest(req, request, res, response);
        if (postParseSuccess) {
            //check valves if we support async
            request.setAsyncSupported(
                connector.getService()
                		.getContainer()
                		.getPipeline()
                		.isAsyncSupported());
            // 由 Pipeline 处理流程，见Pipeline篇
            connector.getService()
                		.getContainer()
                		.getPipeline()
                		.getFirst()
                		.invoke(request, response);
        }
        // 异步处理
        if (request.isAsync()) {
            // 省略
        } else {
            request.finishRequest();
            response.finishResponse();
        }
    } finally {
        // 处理访问日志，见日志篇
        if (!async && postParseSuccess) {
            Context context = request.getContext();
            if (context != null) {
                context.logAccess(request, response,
                     System.currentTimeMillis() - req.getStartTime(), false);
            }
        }
        req.getRequestProcessor().setWorkerThreadName(null);
        // 回收 request and response
        if (!async) {
            request.recycle();
            response.recycle();
        }
    }
}