TOMCA源码分析——处理请求分析（上）

　在《TOMCAT源码分析——请求原理分析（上）》一文中已经介绍了关于Tomcat7.0处理请求前作的初始化和准备工作，请读者在阅读本文前确保掌握《TOMCAT源码分析——请求原理分析（上）》一文中的相关知识以及HTTP协议和TCP协议的一些内容。本文重点讲解Tomcat7.0在准备好接受请求后，请求过程的原理分析。

请求处理架构

　　在正式开始之前，我们先来看看图1中的Tomcat请求处理架构。

图1　　Tomcat请求处理架构

图1列出了Tomcat请求处理架构中的主要组件，这里对它们做个简单介绍：

• Acceptor：负责从ServerSocket中接收新的连接，并将Socket转交给SocketProcessor处理。Acceptor是AbstractEndpoint的内部类，其实现已在《TOMCAT源码分析——请求原理分析（上）》一文中介绍。Acceptor线程的默认大小为1，我们可以在server.xml的Connector配置中增加acceptorThreadCount的大小。
• SocketProcessor：负责对Acceptor转交的Socket进行处理，包括给Socket设置属性、读取请求行和请求头等，最终将处理交给Engine的Pipeline处理。
• ThreadPool：执行SocketProcessor的线程来自《TOMCAT源码分析——请求原理分析（上）》一文中介绍的线程池，此线程池默认的最小线程数minSpareThreads等于10，最大线程数maxThreads等于200，我们可以在server.xml的Connector配置中调整它们的大小。
• Pipeline：SocketProcessor线程最后会将请求进一步交给Engine容器的Pipeline，管道Pipeline包括一系列的valve，如：StandardEngineValve、AccessLogValve、ErrorReportValve、StandardHostValve、 StandardContextValve、 StandardWrapperValve，它们就像地下水管中的一个个阀门，每一个都会对请求数据做不同的处理。
• FilterChain：管道Pipeline的最后一个valve是StandardWrapperValve，它会负责生成Servlet和Filter实例，并将它们组织成对请求处理的链条，这里正是Tomcat与J2EE规范相结合的部分。

　　默认情况下，Tomcat只有一个Acceptor线程，Acceptor不断循环从ServerSocket中获取Socket，当并发数大的情况下，这里会不会有性能问题？我想说的是，Acceptor的实现非常轻量级，它只负责两个动作：获取Socket和将Socket转交给SocketProcessor线程处理。另外，我们可以通过在server.xml的Connector配置中增加acceptorThreadCount的值，让我们同时可以拥有多个Acceptor线程。虽然我们可以修改maxThreads配置把SocketProcessor的线程数设置的很大，但是我们需要区别对待：

• 如果你部署在Tomcat上的Web服务主要用于计算，那么CPU的开销势必会很大，那么线程数不宜设置的过大，一般以CPU核数*2——CPU核数*3最佳。当然如果计算量非常大，就已经超出了Tomcat的使用范畴，我想此时，选择离线计算框架Hadoop或者实时计算框架Storm、Spark才是更好的选择。
• 如果部署在Tomcat上的Web服务主要是为了提供数据库访问，此时I/O的开销会很大，而CPU利用率反而低，此时应该将线程数设置的大一些，但是如果设置的过大，CPU为了给成百上千个线程分配时间片，造成CPU的精力都分散在线程切换上，反而造成性能下降。具体多大，需要对系统性能调优得出。

　　原理就讲这么多，下面具体分析下Tomcat处理请求的具体实现。

接收请求

　　在《TOMCAT源码分析——请求原理分析（上）》一文中我们曾经介绍过AbstractEndpoint的内部类Acceptor，Acceptor实现了Runnable接口。Acceptor作为后台线程不断循环，每次循环都会sleep大约1秒钟（由于是线程级别的，所以并不保证准确），然后接收来自浏览器的Socket连接（用户在浏览器输入HTTP请求地址后，浏览器底层实际使用Socket通信的），最后将Socket交给外部类AbstractEndpoint的processSocket方法（见代码清单1）处理。

代码清单1

// ---------------------------------------------- Request processing methods

    /**
     * Process the given SocketWrapper with the given status. Used to trigger
     * processing as if the Poller (for those endpoints that have one)
     * selected the socket.
     *
     * @param socketWrapper The socket wrapper to process
     * @param event         The socket event to be processed
     * @param dispatch      Should the processing be performed on a new
     *                          container thread
     *
     * @return if processing was triggered successfully
     */
    public boolean processSocket(SocketWrapperBase<S> socketWrapper,
            SocketEvent event, boolean dispatch) {
        try {
            if (socketWrapper == null) {
                return false;
            }
            SocketProcessorBase<S> sc = processorCache.pop();
            if (sc == null) {
                sc = createSocketProcessor(socketWrapper, event);
            } else {
                sc.reset(socketWrapper, event);
            }
            Executor executor = getExecutor();
            if (dispatch && executor != null) {
                executor.execute(sc);
            } else {
                sc.run();
            }
        } catch (RejectedExecutionException ree) {
            getLog().warn(sm.getString("endpoint.executor.fail", socketWrapper) , ree);
            return false;
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            // This means we got an OOM or similar creating a thread, or that
            // the pool and its queue are full
            getLog().error(sm.getString("endpoint.process.fail"), t);
            return false;
        }
        return true;
    }

根据代码清单1，AbstractEndpoint的processSocket方法的处理步骤如下：

1. 通过无界的LIFO同步队列获取SocketProcessorBase，如果没有则创建；
2. 获取线程池对象并使用线程池（此线程池已在《TOMCAT源码分析——请求原理分析（上）》一文中启动PROTOCOLHANDLER一节介绍）执行。

代码清单2

@Override
    protected SocketProcessorBase<NioChannel> createSocketProcessor(
            SocketWrapperBase<NioChannel> socketWrapper, SocketEvent event) {
        return new SocketProcessor(socketWrapper, event);
    }

代码清单3

// ---------------------------------------------- SocketProcessor Inner Class

    /**
     * This class is the equivalent of the Worker, but will simply use in an
     * external Executor thread pool.
     */
    protected class SocketProcessor extends SocketProcessorBase<NioChannel> {

        public SocketProcessor(SocketWrapperBase<NioChannel> socketWrapper, SocketEvent event) {
            super(socketWrapper, event);
        }

        @Override
        protected void doRun() {
            NioChannel socket = socketWrapper.getSocket();
            SelectionKey key = socket.getIOChannel().keyFor(socket.getPoller().getSelector());

            try {
                int handshake = -1;

                try {
                    if (key != null) {
                        if (socket.isHandshakeComplete()) {
                            // No TLS handshaking required. Let the handler
                            // process this socket / event combination.
                            handshake = 0;
                        } else if (event == SocketEvent.STOP || event == SocketEvent.DISCONNECT ||
                                event == SocketEvent.ERROR) {
                            // Unable to complete the TLS handshake. Treat it as
                            // if the handshake failed.
                            handshake = -1;
                        } else {
                            handshake = socket.handshake(key.isReadable(), key.isWritable());
                            // The handshake process reads/writes from/to the
                            // socket. status may therefore be OPEN_WRITE once
                            // the handshake completes. However, the handshake
                            // happens when the socket is opened so the status
                            // must always be OPEN_READ after it completes. It
                            // is OK to always set this as it is only used if
                            // the handshake completes.
                            event = SocketEvent.OPEN_READ;
                        }
                    }
                } catch (IOException x) {
                    handshake = -1;
                    if (log.isDebugEnabled()) log.debug("Error during SSL handshake",x);
                } catch (CancelledKeyException ckx) {
                    handshake = -1;
                }
                if (handshake == 0) {
                    SocketState state = SocketState.OPEN;
                    // Process the request from this socket
                    if (event == null) {
                        state = getHandler().process(socketWrapper, SocketEvent.OPEN_READ);
                    } else {
                        state = getHandler().process(socketWrapper, event);
                    }
                    if (state == SocketState.CLOSED) {
                        close(socket, key);
                    }
                } else if (handshake == -1 ) {
                    close(socket, key);
                } else if (handshake == SelectionKey.OP_READ){
                    socketWrapper.registerReadInterest();
                } else if (handshake == SelectionKey.OP_WRITE){
                    socketWrapper.registerWriteInterest();
                }
            } catch (CancelledKeyException cx) {
                socket.getPoller().cancelledKey(key);
            } catch (VirtualMachineError vme) {
                ExceptionUtils.handleThrowable(vme);
            } catch (Throwable t) {
                log.error("", t);
                socket.getPoller().cancelledKey(key);
            } finally {
                socketWrapper = null;
                event = null;
                //return to cache
                if (running && !paused) {
                    processorCache.push(this);
                }
            }
        }
    }

SocketProcessor线程专门用于处理Acceptor转交的Socket，其执行步骤如下：

1. 调用handler的process方法处理请求。在《TOMCAT源码分析——请求原理分析（上）》一文中我们讲过当处理AbstractProtocol协议时，handler默认为AbstractProtocol的内部类ConnectionHandler；
2. 请求处理完毕后，如果state等于SocketState.CLOSED，则关闭Socket；如果state等于SocketState.OPEN，则保持连接；如果state等于SocketState.LONG，则会作为长连接对待。
3. 最后把process归还到processorCache(LIFO的同步栈SynchronizedStack)栈中

以ConnectionHandler为例，我们重点分析它是如何进一步处理Socket的。ConnectionHandler的process方法，见代码清单6。

代码清单6

@Override
        public SocketState process(SocketWrapperBase<S> wrapper, SocketEvent status) {
            if (getLog().isDebugEnabled()) {
                getLog().debug(sm.getString("abstractConnectionHandler.process",
                        wrapper.getSocket(), status));
            }
            if (wrapper == null) {
                // Nothing to do. Socket has been closed.
                return SocketState.CLOSED;
            }

            S socket = wrapper.getSocket();

            Processor processor = connections.get(socket);
            if (getLog().isDebugEnabled()) {
                getLog().debug(sm.getString("abstractConnectionHandler.connectionsGet",
                        processor, socket));
            }

            if (processor != null) {
                // Make sure an async timeout doesn't fire
                getProtocol().removeWaitingProcessor(processor);
            } else if (status == SocketEvent.DISCONNECT || status == SocketEvent.ERROR) {
                // Nothing to do. Endpoint requested a close and there is no
                // longer a processor associated with this socket.
                return SocketState.CLOSED;
            }

            ContainerThreadMarker.set();

            try {
                if (processor == null) {
                    String negotiatedProtocol = wrapper.getNegotiatedProtocol();
                    if (negotiatedProtocol != null) {
                        UpgradeProtocol upgradeProtocol =
                                getProtocol().getNegotiatedProtocol(negotiatedProtocol);
                        if (upgradeProtocol != null) {
                            processor = upgradeProtocol.getProcessor(
                                    wrapper, getProtocol().getAdapter());
                        } else if (negotiatedProtocol.equals("http/1.1")) {
                            // Explicitly negotiated the default protocol.
                            // Obtain a processor below.
                        } else {
                            // TODO:
                            // OpenSSL 1.0.2's ALPN callback doesn't support
                            // failing the handshake with an error if no
                            // protocol can be negotiated. Therefore, we need to
                            // fail the connection here. Once this is fixed,
                            // replace the code below with the commented out
                            // block.
                            if (getLog().isDebugEnabled()) {
                                getLog().debug(sm.getString(
                                    "abstractConnectionHandler.negotiatedProcessor.fail",
                                    negotiatedProtocol));
                            }
                            return SocketState.CLOSED;
                            /*
                             * To replace the code above once OpenSSL 1.1.0 is
                             * used.
                            // Failed to create processor. This is a bug.
                            throw new IllegalStateException(sm.getString(
                                    "abstractConnectionHandler.negotiatedProcessor.fail",
                                    negotiatedProtocol));
                            */
                        }
                    }
                }
                if (processor == null) {
                    processor = recycledProcessors.pop();
                    if (getLog().isDebugEnabled()) {
                        getLog().debug(sm.getString("abstractConnectionHandler.processorPop",
                                processor));
                    }
                }
                if (processor == null) {
                    processor = getProtocol().createProcessor();
                    register(processor);
                }

                processor.setSslSupport(
                        wrapper.getSslSupport(getProtocol().getClientCertProvider()));

                // Associate the processor with the connection
                connections.put(socket, processor);

                SocketState state = SocketState.CLOSED;
                do {
　　　　　　　　　　　　//AbstractProcessorLight类的process方法
                    state = processor.process(wrapper, status);

                    if (state == SocketState.UPGRADING) {
                        // Get the HTTP upgrade handler
                        UpgradeToken upgradeToken = processor.getUpgradeToken();
                        // Retrieve leftover input
                        ByteBuffer leftOverInput = processor.getLeftoverInput();
                        if (upgradeToken == null) {
                            // Assume direct HTTP/2 connection
                            UpgradeProtocol upgradeProtocol = getProtocol().getUpgradeProtocol("h2c");
                            if (upgradeProtocol != null) {
                                processor = upgradeProtocol.getProcessor(
                                        wrapper, getProtocol().getAdapter());
                                wrapper.unRead(leftOverInput);
                                // Associate with the processor with the connection
                                connections.put(socket, processor);
                            } else {
                                if (getLog().isDebugEnabled()) {
                                    getLog().debug(sm.getString(
                                        "abstractConnectionHandler.negotiatedProcessor.fail",
                                        "h2c"));
                                }
                                return SocketState.CLOSED;
                            }
                        } else {
                            HttpUpgradeHandler httpUpgradeHandler = upgradeToken.getHttpUpgradeHandler();
                            // Release the Http11 processor to be re-used
                            release(processor);
                            // Create the upgrade processor
                            processor = getProtocol().createUpgradeProcessor(wrapper, upgradeToken);
                            if (getLog().isDebugEnabled()) {
                                getLog().debug(sm.getString("abstractConnectionHandler.upgradeCreate",
                                        processor, wrapper));
                            }
                            wrapper.unRead(leftOverInput);
                            // Mark the connection as upgraded
                            wrapper.setUpgraded(true);
                            // Associate with the processor with the connection
                            connections.put(socket, processor);
                            // Initialise the upgrade handler (which may trigger
                            // some IO using the new protocol which is why the lines
                            // above are necessary)
                            // This cast should be safe. If it fails the error
                            // handling for the surrounding try/catch will deal with
                            // it.
                            if (upgradeToken.getInstanceManager() == null) {
                                httpUpgradeHandler.init((WebConnection) processor);
                            } else {
                                ClassLoader oldCL = upgradeToken.getContextBind().bind(false, null);
                                try {
                                    httpUpgradeHandler.init((WebConnection) processor);
                                } finally {
                                    upgradeToken.getContextBind().unbind(false, oldCL);
                                }
                            }
                        }
                    }
                } while ( state == SocketState.UPGRADING);

                if (state == SocketState.LONG) {
                    // In the middle of processing a request/response. Keep the
                    // socket associated with the processor. Exact requirements
                    // depend on type of long poll
                    longPoll(wrapper, processor);
                    if (processor.isAsync()) {
                        getProtocol().addWaitingProcessor(processor);
                    }
                } else if (state == SocketState.OPEN) {
                    // In keep-alive but between requests. OK to recycle
                    // processor. Continue to poll for the next request.
                    connections.remove(socket);
                    release(processor);
                    wrapper.registerReadInterest();
                } else if (state == SocketState.SENDFILE) {
                    // Sendfile in progress. If it fails, the socket will be
                    // closed. If it works, the socket either be added to the
                    // poller (or equivalent) to await more data or processed
                    // if there are any pipe-lined requests remaining.
                } else if (state == SocketState.UPGRADED) {
                    // Don't add sockets back to the poller if this was a
                    // non-blocking write otherwise the poller may trigger
                    // multiple read events which may lead to thread starvation
                    // in the connector. The write() method will add this socket
                    // to the poller if necessary.
                    if (status != SocketEvent.OPEN_WRITE) {
                        longPoll(wrapper, processor);
                    }
                } else if (state == SocketState.SUSPENDED) {
                    // Don't add sockets back to the poller.
                    // The resumeProcessing() method will add this socket
                    // to the poller.
                } else {
                    // Connection closed. OK to recycle the processor. Upgrade
                    // processors are not recycled.
                    connections.remove(socket);
                    if (processor.isUpgrade()) {
                        UpgradeToken upgradeToken = processor.getUpgradeToken();
                        HttpUpgradeHandler httpUpgradeHandler = upgradeToken.getHttpUpgradeHandler();
                        InstanceManager instanceManager = upgradeToken.getInstanceManager();
                        if (instanceManager == null) {
                            httpUpgradeHandler.destroy();
                        } else {
                            ClassLoader oldCL = upgradeToken.getContextBind().bind(false, null);
                            try {
                                httpUpgradeHandler.destroy();
                            } finally {
                                try {
                                    instanceManager.destroyInstance(httpUpgradeHandler);
                                } catch (Throwable e) {
                                    ExceptionUtils.handleThrowable(e);
                                    getLog().error(sm.getString("abstractConnectionHandler.error"), e);
                                }
                                upgradeToken.getContextBind().unbind(false, oldCL);
                            }
                        }
                    } else {
                        release(processor);
                    }
                }
                return state;
            } catch(java.net.SocketException e) {
                // SocketExceptions are normal
                getLog().debug(sm.getString(
                        "abstractConnectionHandler.socketexception.debug"), e);
            } catch (java.io.IOException e) {
                // IOExceptions are normal
                getLog().debug(sm.getString(
                        "abstractConnectionHandler.ioexception.debug"), e);
            } catch (ProtocolException e) {
                // Protocol exceptions normally mean the client sent invalid or
                // incomplete data.
                getLog().debug(sm.getString(
                        "abstractConnectionHandler.protocolexception.debug"), e);
            }
            // Future developers: if you discover any other
            // rare-but-nonfatal exceptions, catch them here, and log as
            // above.
            catch (Throwable e) {
                ExceptionUtils.handleThrowable(e);
                // any other exception or error is odd. Here we log it
                // with "ERROR" level, so it will show up even on
                // less-than-verbose logs.
                getLog().error(sm.getString("abstractConnectionHandler.error"), e);
            } finally {
                ContainerThreadMarker.clear();
            }

            // Make sure socket/processor is removed from the list of current
            // connections
            connections.remove(socket);
            release(processor);
            return SocketState.CLOSED;
        }

根据代码清单6，可见ConnectionHandler的process方法的处理步骤如下：

1. 先从connections(同步的map)中获取processor，假如有，则删除等待的processor。
2. 然后再通过getNegotiatedProtocol获取processor。
3. 从可以循环使用的recycledProcessors（类型为ConcurrentLinkedQueue）中获取；如果recycledProcessors中也没有可以使用的processor，则调用createProcessor方法（见代码清单7）创建AbstractHttp11Protocol；
4. 如果当前Connector配置了指定了SSLEnabled="true"，那么还需要给AbstractHttp11Protocol设置SSL相关的属性；
5. 如果Socket是异步的，则调用AbstractProcessorLight的asyncPostProcess方法，否则调用AbstractProcessorLight的service(socketWrapper)方法；
6. 请求处理完毕，如果Socket是UPGRADING的，则将Socket和AbstractHttp11Protocol一起放入connections缓存，否则从connections缓存中移除Socket和AbstractHttp11Protocol。

AbstractProcessorLight类的process方法：

@Override
    public SocketState process(SocketWrapperBase<?> socketWrapper, SocketEvent status)
            throws IOException {

        SocketState state = SocketState.CLOSED;
        Iterator<DispatchType> dispatches = null;
        do {
            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) {
                    // There may be pipe-lined data to read. If the data isn't
                    // processed now, execution will exit this loop and call
                    // release() which will recycle the processor (and input
                    // buffer) deleting any pipe-lined data. To avoid this,
                    // process it now.
　　　　　　　　　　　　
　　　　　　　　　　　　//Http11Processor.service()
                    state = service(socketWrapper);
                }
            } else if (status == SocketEvent.OPEN_WRITE) {
                // Extra write event likely after async, ignore
                state = SocketState.LONG;
            } else if (status == SocketEvent.OPEN_READ){
　　　　　　　　　　//Http11Processor.service()
                state = service(socketWrapper);
            } else {
                // Default to closing the socket if the SocketEvent passed in
                // is not consistent with the current state of the Processor
                state = SocketState.CLOSED;
            }

            if (state != SocketState.CLOSED && isAsync()) {
                state = asyncPostProcess();
            }

            if (getLog().isDebugEnabled()) {
                getLog().debug("Socket: [" + socketWrapper +
                        "], Status in: [" + status +
                        "], State out: [" + state + "]");
            }

            if (dispatches == null || !dispatches.hasNext()) {
                // Only returns non-null iterator if there are
                // dispatches to process.
                dispatches = getIteratorAndClearDispatches();
            }
        } while (state == SocketState.ASYNC_END ||
                dispatches != null && state != SocketState.CLOSED);

        return state;
    }

代码清单7

// ------------------------------------------------------------- Common code

    @SuppressWarnings("deprecation")
    @Override
    protected Processor createProcessor() {
        Http11Processor processor = new Http11Processor(getMaxHttpHeaderSize(),
                getAllowHostHeaderMismatch(), getRejectIllegalHeaderName(), getEndpoint(),
                getMaxTrailerSize(), allowedTrailerHeaders, getMaxExtensionSize(),
                getMaxSwallowSize(), httpUpgradeProtocols, getSendReasonPhrase());
        processor.setAdapter(getAdapter());
        processor.setMaxKeepAliveRequests(getMaxKeepAliveRequests());
        processor.setConnectionUploadTimeout(getConnectionUploadTimeout());
        processor.setDisableUploadTimeout(getDisableUploadTimeout());
        processor.setCompressionMinSize(getCompressionMinSize());
        processor.setCompression(getCompression());
        processor.setNoCompressionUserAgents(getNoCompressionUserAgents());
        processor.setCompressibleMimeTypes(getCompressibleMimeTypes());
        processor.setRestrictedUserAgents(getRestrictedUserAgents());
        processor.setMaxSavePostSize(getMaxSavePostSize());
        processor.setServer(getServer());
        processor.setServerRemoveAppProvidedValues(getServerRemoveAppProvidedValues());
        return processor;
    }

根据之前的分析，我们知道Socket的处理方式有异步和同步两种，调用Http11Processor的asyncPostProcess和service方法，我们以同步处理为例，来看看接下来的处理逻辑。

同步处理

　　Http11Processor的service方法（见代码清单8）用于同步处理，由于其代码很多，所以此处在代码后面追加一些注释，便于读者理解。这里面有一些关键方法重点拿出来解释下：

1. InternalInputBuffer的parseRequestLine方法用于读取请求行；
2. InternalInputBuffer的parseHeaders方法用于读取请求头；
3. prepareRequest用于在正式处理请求之前，做一些准备工作，如根据请求头获取请求的版本号是HTTP/1.1还是HTTP/0.9、keepAlive是否为true等，还会设置一些输入过滤器用于标记请求、压缩等；
4. 调用CoyoteAdapter的service方法处理请求。

代码清单8

@Override
    public SocketState service(SocketWrapperBase<?> socketWrapper)
        throws IOException {
        RequestInfo rp = request.getRequestProcessor();
        rp.setStage(org.apache.coyote.Constants.STAGE_PARSE);

        // Setting up the I/O
        setSocketWrapper(socketWrapper);
        inputBuffer.init(socketWrapper);
        outputBuffer.init(socketWrapper);

        // Flags
        keepAlive = true;
        openSocket = false;
        readComplete = true;
        boolean keptAlive = false;
        SendfileState sendfileState = SendfileState.DONE;

        while (!getErrorState().isError() && keepAlive && !isAsync() && upgradeToken == null &&
                sendfileState == SendfileState.DONE && !endpoint.isPaused()) {

            // Parsing the request header
            try {
                if (!inputBuffer.parseRequestLine(keptAlive)) {
                    if (inputBuffer.getParsingRequestLinePhase() == -1) {
                        return SocketState.UPGRADING;
                    } else if (handleIncompleteRequestLineRead()) {
                        break;
                    }
                }

                if (endpoint.isPaused()) {
                    // 503 - Service unavailable
                    response.setStatus(503);
                    setErrorState(ErrorState.CLOSE_CLEAN, null);
                } else {
                    keptAlive = true;
                    // Set this every time in case limit has been changed via JMX
                    request.getMimeHeaders().setLimit(endpoint.getMaxHeaderCount());
                    if (!inputBuffer.parseHeaders()) {
                        // We've read part of the request, don't recycle it
                        // instead associate it with the socket
                        openSocket = true;
                        readComplete = false;
                        break;
                    }
                    if (!disableUploadTimeout) {
                        socketWrapper.setReadTimeout(connectionUploadTimeout);
                    }
                }
            } catch (IOException e) {
                if (log.isDebugEnabled()) {
                    log.debug(sm.getString("http11processor.header.parse"), e);
                }
                setErrorState(ErrorState.CLOSE_CONNECTION_NOW, e);
                break;
            } catch (Throwable t) {
                ExceptionUtils.handleThrowable(t);
                UserDataHelper.Mode logMode = userDataHelper.getNextMode();
                if (logMode != null) {
                    String message = sm.getString("http11processor.header.parse");
                    switch (logMode) {
                        case INFO_THEN_DEBUG:
                            message += sm.getString("http11processor.fallToDebug");
                            //$FALL-THROUGH$
                        case INFO:
                            log.info(message, t);
                            break;
                        case DEBUG:
                            log.debug(message, t);
                    }
                }
                // 400 - Bad Request
                response.setStatus(400);
                setErrorState(ErrorState.CLOSE_CLEAN, t);
                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)) {
                        // TODO Figure out how to handle request bodies at this
                        // point.
                        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()) {
                // Setting up filters, and parse some request headers
                rp.setStage(org.apache.coyote.Constants.STAGE_PREPARE);
                try {
                    prepareRequest();
                } catch (Throwable t) {
                    ExceptionUtils.handleThrowable(t);
                    if (log.isDebugEnabled()) {
                        log.debug(sm.getString("http11processor.request.prepare"), 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;
            }

            // Process the request in the adapter
            if (!getErrorState().isError()) {
                try {
                    rp.setStage(org.apache.coyote.Constants.STAGE_SERVICE);
                    getAdapter().service(request, response);
                    // Handle when the response was committed before a serious
                    // error occurred.  Throwing a ServletException should both
                    // set the status to 500 and set the errorException.
                    // If we fail here, then the response is likely already
                    // committed, so we can't try and set headers.
                    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) {
                    log.error(sm.getString("http11processor.request.process"), e);
                    // The response should not have been committed but check it
                    // anyway to be safe
                    if (response.isCommitted()) {
                        setErrorState(ErrorState.CLOSE_NOW, e);
                    } else {
                        response.reset();
                        response.setStatus(500);
                        setErrorState(ErrorState.CLOSE_CLEAN, e);
                        response.setHeader("Connection", "close"); // TODO: Remove
                    }
                } catch (Throwable t) {
                    ExceptionUtils.handleThrowable(t);
                    log.error(sm.getString("http11processor.request.process"), 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()) {
                // If this is an async request then the request ends when it has
                // been completed. The AsyncContext is responsible for calling
                // endRequest() in that case.
                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);

        if (getErrorState().isError() || endpoint.isPaused()) {
            return SocketState.CLOSED;
        } else if (isAsync()) {
            return SocketState.LONG;
        } else if (isUpgrade()) {
            return SocketState.UPGRADING;
        } else {
            if (sendfileState == SendfileState.PENDING) {
                return SocketState.SENDFILE;
            } else {
                if (openSocket) {
                    if (readComplete) {
                        return SocketState.OPEN;
                    } else {
                        return SocketState.LONG;
                    }
                } else {
                    return SocketState.CLOSED;
                }
            }
        }
    }

从代码清单8可以看出，最后的请求处理交给了CoyoteAdapter，CoyoteAdapter的service方法（见代码清单9）用于真正处理请求。

代码清单9

@Override
    public void service(org.apache.coyote.Request req, org.apache.coyote.Response res)
            throws Exception {

        Request request = (Request) req.getNote(ADAPTER_NOTES);
        Response response = (Response) res.getNote(ADAPTER_NOTES);

        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());
        }

        if (connector.getXpoweredBy()) {
            response.addHeader("X-Powered-By", POWERED_BY);
        }

        boolean async = false;
        boolean postParseSuccess = false;

        req.getRequestProcessor().setWorkerThreadName(THREAD_NAME.get());

        try {
            // Parse and set Catalina and configuration specific
            // request parameters
            postParseSuccess = postParseRequest(req, request, res, response);
            if (postParseSuccess) {
                //check valves if we support async
                request.setAsyncSupported(
                        connector.getService().getContainer().getPipeline().isAsyncSupported());
                // Calling the container
                connector.getService().getContainer().getPipeline().getFirst().invoke(
                        request, response);
            }
            if (request.isAsync()) {
                async = true;
                ReadListener readListener = req.getReadListener();
                if (readListener != null && request.isFinished()) {
                    // Possible the all data may have been read during service()
                    // method so this needs to be checked here
                    ClassLoader oldCL = null;
                    try {
                        oldCL = request.getContext().bind(false, null);
                        if (req.sendAllDataReadEvent()) {
                            req.getReadListener().onAllDataRead();
                        }
                    } finally {
                        request.getContext().unbind(false, oldCL);
                    }
                }

                Throwable throwable =
                        (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION);

                // If an async request was started, is not going to end once
                // this container thread finishes and an error occurred, trigger
                // the async error process
                if (!request.isAsyncCompleting() && throwable != null) {
                    request.getAsyncContextInternal().setErrorState(throwable, true);
                }
            } else {
                request.finishRequest();
                response.finishResponse();
            }

        } catch (IOException e) {
            // Ignore
        } finally {
            AtomicBoolean error = new AtomicBoolean(false);
            res.action(ActionCode.IS_ERROR, error);

            if (request.isAsyncCompleting() && error.get()) {
                // Connection will be forcibly closed which will prevent
                // completion happening at the usual point. Need to trigger
                // call to onComplete() here.
                res.action(ActionCode.ASYNC_POST_PROCESS,  null);
                async = false;
            }

            // Access log
            if (!async && postParseSuccess) {
                // Log only if processing was invoked.
                // If postParseRequest() failed, it has already logged it.
                Context context = request.getContext();
                // If the context is null, it is likely that the endpoint was
                // shutdown, this connection closed and the request recycled in
                // a different thread. That thread will have updated the access
                // log so it is OK not to update the access log here in that
                // case.
                if (context != null) {
                    context.logAccess(request, response,
                            System.currentTimeMillis() - req.getStartTime(), false);
                }
            }

            req.getRequestProcessor().setWorkerThreadName(null);

            // Recycle the wrapper request and response
            if (!async) {
                request.recycle();
                response.recycle();
            }
        }
    }

从代码清单9可以看出，CoyoteAdapter的service方法的执行步骤如下：

1. 创建Request与Response对象并且关联起来；
2. 调用postParseRequest方法（见代码清单10）对请求进行解析；

3. 将真正的请求处理交给Engine的Pipeline去处理，代码：connector.getService().getContainer().getPipeline().getFirst().invoke(request, response);

代码清单10

protected boolean postParseRequest(org.apache.coyote.Request req, Request request,
            org.apache.coyote.Response res, Response response) throws IOException, ServletException {

        // If the processor has set the scheme (AJP does this, HTTP does this if
        // SSL is enabled) use this to set the secure flag as well. If the
        // processor hasn't set it, use the settings from the connector
        if (req.scheme().isNull()) {
            // Use connector scheme and secure configuration, (defaults to
            // "http" and false respectively)
            req.scheme().setString(connector.getScheme());
            request.setSecure(connector.getSecure());
        } else {
            // Use processor specified scheme to determine secure state
            request.setSecure(req.scheme().equals("https"));
        }

        // At this point the Host header has been processed.
        // Override if the proxyPort/proxyHost are set
        String proxyName = connector.getProxyName();
        int proxyPort = connector.getProxyPort();
        if (proxyPort != 0) {
            req.setServerPort(proxyPort);
        } else if (req.getServerPort() == -1) {
            // Not explicitly set. Use default ports based on the scheme
            if (req.scheme().equals("https")) {
                req.setServerPort(443);
            } else {
                req.setServerPort(80);
            }
        }
        if (proxyName != null) {
            req.serverName().setString(proxyName);
        }

        MessageBytes undecodedURI = req.requestURI();

        // Check for ping OPTIONS * request
        if (undecodedURI.equals("*")) {
            if (req.method().equalsIgnoreCase("OPTIONS")) {
                StringBuilder allow = new StringBuilder();
                allow.append("GET, HEAD, POST, PUT, DELETE");
                // Trace if allowed
                if (connector.getAllowTrace()) {
                    allow.append(", TRACE");
                }
                // Always allow options
                allow.append(", OPTIONS");
                res.setHeader("Allow", allow.toString());
            } else {
                res.setStatus(404);
                res.setMessage("Not found");
            }
            connector.getService().getContainer().logAccess(
                    request, response, 0, true);
            return false;
        }

        MessageBytes decodedURI = req.decodedURI();

        if (undecodedURI.getType() == MessageBytes.T_BYTES) {
            // Copy the raw URI to the decodedURI
            decodedURI.duplicate(undecodedURI);

            // Parse the path parameters. This will:
            //   - strip out the path parameters
            //   - convert the decodedURI to bytes
            parsePathParameters(req, request);

            // URI decoding
            // %xx decoding of the URL
            try {
                req.getURLDecoder().convert(decodedURI, false);
            } catch (IOException ioe) {
                res.setStatus(400);
                res.setMessage("Invalid URI: " + ioe.getMessage());
                connector.getService().getContainer().logAccess(
                        request, response, 0, true);
                return false;
            }
            // Normalization
            if (!normalize(req.decodedURI())) {
                res.setStatus(400);
                res.setMessage("Invalid URI");
                connector.getService().getContainer().logAccess(
                        request, response, 0, true);
                return false;
            }
            // Character decoding
            convertURI(decodedURI, request);
            // Check that the URI is still normalized
            if (!checkNormalize(req.decodedURI())) {
                res.setStatus(400);
                res.setMessage("Invalid URI character encoding");
                connector.getService().getContainer().logAccess(
                        request, response, 0, true);
                return false;
            }
        } else {
            /* The URI is chars or String, and has been sent using an in-memory
             * protocol handler. The following assumptions are made:
             * - req.requestURI() has been set to the 'original' non-decoded,
             *   non-normalized URI
             * - req.decodedURI() has been set to the decoded, normalized form
             *   of req.requestURI()
             */
            decodedURI.toChars();
            // Remove all path parameters; any needed path parameter should be set
            // using the request object rather than passing it in the URL
            CharChunk uriCC = decodedURI.getCharChunk();
            int semicolon = uriCC.indexOf(';');
            if (semicolon > 0) {
                decodedURI.setChars
                    (uriCC.getBuffer(), uriCC.getStart(), semicolon);
            }
        }

        // Request mapping.
        MessageBytes serverName;
        if (connector.getUseIPVHosts()) {
            serverName = req.localName();
            if (serverName.isNull()) {
                // well, they did ask for it
                res.action(ActionCode.REQ_LOCAL_NAME_ATTRIBUTE, null);
            }
        } else {
            serverName = req.serverName();
        }

        // Version for the second mapping loop and
        // Context that we expect to get for that version
        String version = null;
        Context versionContext = null;
        boolean mapRequired = true;

        while (mapRequired) {
            // This will map the the latest version by default
            connector.getService().getMapper().map(serverName, decodedURI,
                    version, request.getMappingData());

            // If there is no context at this point, it is likely no ROOT context
            // has been deployed
            if (request.getContext() == null) {
                res.setStatus(404);
                res.setMessage("Not found");
                // No context, so use host
                Host host = request.getHost();
                // Make sure there is a host (might not be during shutdown)
                if (host != null) {
                    host.logAccess(request, response, 0, true);
                }
                return false;
            }

            // Now we have the context, we can parse the session ID from the URL
            // (if any). Need to do this before we redirect in case we need to
            // include the session id in the redirect
            String sessionID;
            if (request.getServletContext().getEffectiveSessionTrackingModes()
                    .contains(SessionTrackingMode.URL)) {

                // Get the session ID if there was one
                sessionID = request.getPathParameter(
                        SessionConfig.getSessionUriParamName(
                                request.getContext()));
                if (sessionID != null) {
                    request.setRequestedSessionId(sessionID);
                    request.setRequestedSessionURL(true);
                }
            }

            // Look for session ID in cookies and SSL session
            parseSessionCookiesId(request);
            parseSessionSslId(request);

            sessionID = request.getRequestedSessionId();

            mapRequired = false;
            if (version != null && request.getContext() == versionContext) {
                // We got the version that we asked for. That is it.
            } else {
                version = null;
                versionContext = null;

                Context[] contexts = request.getMappingData().contexts;
                // Single contextVersion means no need to remap
                // No session ID means no possibility of remap
                if (contexts != null && sessionID != null) {
                    // Find the context associated with the session
                    for (int i = (contexts.length); i > 0; i--) {
                        Context ctxt = contexts[i - 1];
                        if (ctxt.getManager().findSession(sessionID) != null) {
                            // We found a context. Is it the one that has
                            // already been mapped?
                            if (!ctxt.equals(request.getMappingData().context)) {
                                // Set version so second time through mapping
                                // the correct context is found
                                version = ctxt.getWebappVersion();
                                versionContext = ctxt;
                                // Reset mapping
                                request.getMappingData().recycle();
                                mapRequired = true;
                                // Recycle cookies and session info in case the
                                // correct context is configured with different
                                // settings
                                request.recycleSessionInfo();
                                request.recycleCookieInfo(true);
                            }
                            break;
                        }
                    }
                }
            }

            if (!mapRequired && request.getContext().getPaused()) {
                // Found a matching context but it is paused. Mapping data will
                // be wrong since some Wrappers may not be registered at this
                // point.
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    // Should never happen
                }
                // Reset mapping
                request.getMappingData().recycle();
                mapRequired = true;
            }
        }

        // Possible redirect
        MessageBytes redirectPathMB = request.getMappingData().redirectPath;
        if (!redirectPathMB.isNull()) {
            String redirectPath = URLEncoder.DEFAULT.encode(
                    redirectPathMB.toString(), StandardCharsets.UTF_8);
            String query = request.getQueryString();
            if (request.isRequestedSessionIdFromURL()) {
                // This is not optimal, but as this is not very common, it
                // shouldn't matter
                redirectPath = redirectPath + ";" +
                        SessionConfig.getSessionUriParamName(
                            request.getContext()) +
                    "=" + request.getRequestedSessionId();
            }
            if (query != null) {
                // This is not optimal, but as this is not very common, it
                // shouldn't matter
                redirectPath = redirectPath + "?" + query;
            }
            response.sendRedirect(redirectPath);
            request.getContext().logAccess(request, response, 0, true);
            return false;
        }

        // Filter trace method
        if (!connector.getAllowTrace()
                && req.method().equalsIgnoreCase("TRACE")) {
            Wrapper wrapper = request.getWrapper();
            String header = null;
            if (wrapper != null) {
                String[] methods = wrapper.getServletMethods();
                if (methods != null) {
                    for (int i=0; i<methods.length; i++) {
                        if ("TRACE".equals(methods[i])) {
                            continue;
                        }
                        if (header == null) {
                            header = methods[i];
                        } else {
                            header += ", " + methods[i];
                        }
                    }
                }
            }
            res.setStatus(405);
            res.addHeader("Allow", header);
            res.setMessage("TRACE method is not allowed");
            request.getContext().logAccess(request, response, 0, true);
            return false;
        }

        doConnectorAuthenticationAuthorization(req, request);

        return true;
    }

从代码清单10可以看出，postParseRequest方法的执行步骤如下：

1. 解析请求url中的参数；
2. URI decoding的转换；
3. 调用normalize方法判断请求路径中是否存在"\", "//", "/./"和"/../"，如果存在则处理结束；
4. 调用convertURI方法将字节转换为字符；
5. 调用checkNormalize方法判断uri是否存在"\", "//", "/./"和"/../"，如果存在则处理结束；
6. 调用Connector的getMapper方法获取Mapper（已在《TOMCAT源码分析——请求原理分析（上）》一文中介绍），然后调用Mapper的map方法（见代码清单11）对host和context进行匹配（比如http://localhost:8080/manager/status会匹配host：localhost，context：/manager），其实质是调用internalMap方法；
7. 使用ApplicationSessionCookieConfig.getSessionUriParamName获取sessionid的key，然后获取sessionid；
8. 调用parseSessionCookiesId和parseSessionSslId方法查找cookie或者SSL中的sessionid。

代码清单11

/**
     * Map the specified host name and URI, mutating the given mapping data.
     *
     * @param host Virtual host name
     * @param uri URI
     * @param version The version, if any, included in the request to be mapped
     * @param mappingData This structure will contain the result of the mapping
     *                    operation
     * @throws IOException if the buffers are too small to hold the results of
     *                     the mapping.
     */
    public void map(MessageBytes host, MessageBytes uri, String version,
                    MappingData mappingData) throws IOException {

        if (host.isNull()) {
            host.getCharChunk().append(defaultHostName);
        }
        host.toChars();
        uri.toChars();
        internalMap(host.getCharChunk(), uri.getCharChunk(), version,
                mappingData);
    }

CoyoteAdapter的service方法最后会将请求交给Engine的Pipeline去处理，我将在《Tomcat源码分析——请求原理分析（下）》一文中具体讲解。

如需转载，请标明本文作者及出处——作者：jiaan.gja，本文原创首发：博客园，原文链接：http://www.cnblogs.com/jiaan-geng/p/4894832.html