Tomcat源码分析——请求原理分析（中）

前言

　　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JIoEndpoint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JIoEndpoint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JIoEndpoint的processSocket方法（见代码清单1）处理。

代码清单1

    /**
     * Process given socket.
     */
    protected boolean processSocket(Socket socket) {
        try {
            SocketWrapper<Socket> wrapper = new SocketWrapper<Socket>(socket);
            wrapper.setKeepAliveLeft(getMaxKeepAliveRequests());
            getExecutor().execute(new SocketProcessor(wrapper));
        } catch (RejectedExecutionException x) {
            log.warn("Socket processing request was rejected for:"+socket,x);
            return false;
        } catch (Throwable t) {
            // This means we got an OOM or similar creating a thread, or that
            // the pool and its queue are full
            log.error(sm.getString("endpoint.process.fail"), t);
            return false;
        }
        return true;
    }

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

1. 将Socket封装为SocketWrapper；
2. 给SocketWrapper设置连接保持时间keepAliveLeft。这个值是通过调用父类AbstractEndpoint的getMaxKeepAliveRequests方法（见代码清单2）获得的；
3. 创建SocketProcessor（此类也是JIoEndpoint的内部类，而且也实现了Runnable接口，见代码清单3），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

    /**
     * Max keep alive requests
     */
    private int maxKeepAliveRequests=100; // as in Apache HTTPD server
    public int getMaxKeepAliveRequests() {
        return maxKeepAliveRequests;
    }

代码清单3

    /**
     * This class is the equivalent of the Worker, but will simply use in an
     * external Executor thread pool.
     */
    protected class SocketProcessor implements Runnable {

        protected SocketWrapper<Socket> socket = null;
        protected SocketStatus status = null;

        public SocketProcessor(SocketWrapper<Socket> socket) {
            if (socket==null) throw new NullPointerException();
            this.socket = socket;
        }

        public SocketProcessor(SocketWrapper<Socket> socket, SocketStatus status) {
            this(socket);
            this.status = status;
        }

        public void run() {
            boolean launch = false;
            try {

                if (!socket.processing.compareAndSet(false, true)) {
                    log.error("Unable to process socket. Invalid state.");
                    return;
                }

                SocketState state = SocketState.OPEN;
                // Process the request from this socket
                if ( (!socket.isInitialized()) && (!setSocketOptions(socket.getSocket())) ) {
                    state = SocketState.CLOSED;
                }
                socket.setInitialized(true);

                if ( (state != SocketState.CLOSED) ) {
                    state = (status==null)?handler.process(socket):handler.process(socket,status);
                }
                if (state == SocketState.CLOSED) {
                    // Close socket
                    if (log.isTraceEnabled()) {
                        log.trace("Closing socket:"+socket);
                    }
                    try {
                        socket.getSocket().close();
                    } catch (IOException e) {
                        // Ignore
                    }
                } else if (state == SocketState.OPEN){
                    socket.setKeptAlive(true);
                    socket.access();
                    //keepalive connection
                    //TODO - servlet3 check async status, we may just be in a hold pattern
                    launch = true;
                } else if (state == SocketState.LONG) {
                    socket.access();
                    waitingRequests.add(socket);
                }
            } finally {
                socket.processing.set(false);
                if (launch) getExecutor().execute(new SocketProcessor(socket));
                socket = null;
            }
            // Finish up this request

        }

    }

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

1. 调用setSocketOptions方法（见代码清单4）给Socket设置属性，从中可以看到设置属性用到了SocketProperties的setProperties方法（见代码清单5），状态更改为初始化完毕；
2. 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Http11Protocol协议时，handler默认为Http11Protocol的内部类Http11ConnectionHandler；
3. 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。

代码清单4

    /**
     * Set the options for the current socket.
     */
    protected boolean setSocketOptions(Socket socket) {
        // Process the connection

        try {
            // 1: Set socket options: timeout, linger, etc
            socketProperties.setProperties(socket);
        } catch (SocketException s) {
            //error here is common if the client has reset the connection
            if (log.isDebugEnabled()) {
                log.debug(sm.getString("endpoint.err.unexpected"), s);
            }
            // Close the socket
            return false;
        } catch (Throwable t) {
            log.error(sm.getString("endpoint.err.unexpected"), t);
            // Close the socket
            return false;
        }
        try {
            // 2: SSL handshake
            serverSocketFactory.handshake(socket);
        } catch (Throwable t) {
            if (log.isDebugEnabled()) {
                log.debug(sm.getString("endpoint.err.handshake"), t);
            }
            // Tell to close the socket
            return false;
        }
        return true;
    }

代码清单5

    public void setProperties(Socket socket) throws SocketException{
        if (rxBufSize != null)
            socket.setReceiveBufferSize(rxBufSize.intValue());
        if (txBufSize != null)
            socket.setSendBufferSize(txBufSize.intValue());
        if (ooBInline !=null)
            socket.setOOBInline(ooBInline.booleanValue());
        if (soKeepAlive != null)
            socket.setKeepAlive(soKeepAlive.booleanValue());
        if (performanceConnectionTime != null && performanceLatency != null &&
                performanceBandwidth != null)
            socket.setPerformancePreferences(
                    performanceConnectionTime.intValue(),
                    performanceLatency.intValue(),
                    performanceBandwidth.intValue());
        if (soReuseAddress != null)
            socket.setReuseAddress(soReuseAddress.booleanValue());
        if (soLingerOn != null && soLingerTime != null)
            socket.setSoLinger(soLingerOn.booleanValue(),
                    soLingerTime.intValue());
        if (soTimeout != null && soTimeout.intValue() >= 0)
            socket.setSoTimeout(soTimeout.intValue());
        if (tcpNoDelay != null)
            socket.setTcpNoDelay(tcpNoDelay.booleanValue());
        if (soTrafficClass != null)
            socket.setTrafficClass(soTrafficClass.intValue());
    }

以Http11ConnectionHandler为例，我们重点分析它是如何进一步处理Socket的。Http11ConnectionHandler的process方法，见代码清单6。

代码清单6

        public SocketState process(SocketWrapper<Socket> socket) {
            return process(socket,SocketStatus.OPEN);
        }

        public SocketState process(SocketWrapper<Socket> socket, SocketStatus status) {
            Http11Processor processor = connections.remove(socket);
            boolean recycle = true;
            try {
                if (processor == null) {
                    processor = recycledProcessors.poll();
                }
                if (processor == null) {
                    processor = createProcessor();
                }
                processor.action(ActionCode.ACTION_START, null);

                if (proto.isSSLEnabled() && (proto.sslImplementation != null)) {
                    processor.setSSLSupport
                        (proto.sslImplementation.getSSLSupport(socket.getSocket()));
                } else {
                    processor.setSSLSupport(null);
                }

                SocketState state = socket.isAsync()?processor.asyncDispatch(status):processor.process(socket);
                if (state == SocketState.LONG) {
                    connections.put(socket, processor);
                    socket.setAsync(true);
                    recycle = false;
                } else {
                    connections.remove(socket);
                    socket.setAsync(false);
                }
                return state;
            } catch(java.net.SocketException e) {
                // SocketExceptions are normal
                Http11Protocol.log.debug
                    (sm.getString
                     ("http11protocol.proto.socketexception.debug"), e);
            } catch (java.io.IOException e) {
                // IOExceptions are normal
                Http11Protocol.log.debug
                    (sm.getString
                     ("http11protocol.proto.ioexception.debug"), e);
            }
            // Future developers: if you discover any other
            // rare-but-nonfatal exceptions, catch them here, and log as
            // above.
            catch (Throwable 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.
                Http11Protocol.log.error
                    (sm.getString("http11protocol.proto.error"), e);
            } finally {
                //       if(proto.adapter != null) proto.adapter.recycle();
                //                processor.recycle();

                if (recycle) {
                    processor.action(ActionCode.ACTION_STOP, null);
                    recycledProcessors.offer(processor);
                }
            }
            return SocketState.CLOSED;
        }

根据代码清单6，可见Http11ConnectionHandler的process方法的处理步骤如下：

1. 从Socket的连接缓存connections中获取依然Socket对应的Http11Processor；如果连接缓存connections中不存在Socket对应的Http11Processor，则从可以循环使用的recycledProcessors（类型为ConcurrentLinkedQueue）中获取；如果recycledProcessors中也没有可以使用的Http11Processor，则调用createProcessor方法（见代码清单7）创建Http11Processor；
2. 如果当前Connector配置了指定了SSLEnabled="true"，那么还需要给Http11Processor设置SSL相关的属性；
3. 如果Socket是异步的，则调用Http11Processor的asyncDispatch方法，否则调用Http11Processor的process方法；
4. 请求处理完毕，如果Socket是长连接的，则将Socket和Http11Processor一起放入connections缓存，否则从connections缓存中移除Socket和Http11Processor。

代码清单7

        protected Http11Processor createProcessor() {
            Http11Processor processor =
                new Http11Processor(proto.getMaxHttpHeaderSize(), (JIoEndpoint)proto.endpoint);
            processor.setAdapter(proto.adapter);
            processor.setMaxKeepAliveRequests(proto.getMaxKeepAliveRequests());
            processor.setKeepAliveTimeout(proto.getKeepAliveTimeout());
            processor.setTimeout(proto.getTimeout());
            processor.setDisableUploadTimeout(proto.getDisableUploadTimeout());
            processor.setCompressionMinSize(proto.getCompressionMinSize());
            processor.setCompression(proto.getCompression());
            processor.setNoCompressionUserAgents(proto.getNoCompressionUserAgents());
            processor.setCompressableMimeTypes(proto.getCompressableMimeTypes());
            processor.setRestrictedUserAgents(proto.getRestrictedUserAgents());
            processor.setSocketBuffer(proto.getSocketBuffer());
            processor.setMaxSavePostSize(proto.getMaxSavePostSize());
            processor.setServer(proto.getServer());
            register(processor);
            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，分别调用Http11Processor的asyncDispatch方法或process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process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

　　　　　　　RequestInfo rp = request.getRequestProcessor();
　　　　　　　rp.setStage(org.apache.coyote.Constants.STAGE_PARSE);
　　　　　　　this.socket = socketWrapper;
　　　　　　　inputBuffer.setInputStream(socket.getSocket().getInputStream());//设置输入流
　　　　　　　outputBuffer.setOutputStream(socket.getSocket().getOutputStream());//设置输出流
　　　　　　　int keepAliveLeft = maxKeepAliveRequests>0?socketWrapper.decrementKeepAlive():-1;//保持连接递减
　　　　　　　int soTimeout = endpoint.getSoTimeout();//socket超时时间
　　　　　　　socket.getSocket().setSoTimeout(soTimeout);//设置超时时间
　　　　　　　boolean keptAlive = socketWrapper.isKeptAlive();//是否保持连接
　　　　　　　while (started && !error && keepAlive) {

            // Parsing the request header
            try {
                //TODO - calculate timeout based on length in queue (System.currentTimeMills() - wrapper.getLastAccess() is the time in queue)
                if (keptAlive) {//是否保持连接
                    if (keepAliveTimeout > 0) {
                        socket.getSocket().setSoTimeout(keepAliveTimeout);
                    }
                    else if (soTimeout > 0) {
                        socket.getSocket().setSoTimeout(soTimeout);
                    }
                }
　　　　　　　　　 inputBuffer.parseRequestLine(false);//读取请求行
                request.setStartTime(System.currentTimeMillis());
                keptAlive = true;
                if (disableUploadTimeout) {
                    socket.getSocket().setSoTimeout(soTimeout);
                } else {
                    socket.getSocket().setSoTimeout(timeout);
                }
                inputBuffer.parseHeaders();//解析请求头
            } catch (IOException e) {
                error = true;
                break;
            } catch (Throwable t) {
                if (log.isDebugEnabled()) {
                    log.debug(sm.getString("http11processor.header.parse"), t);
                }
                // 400 - Bad Request
                response.setStatus(400);
                adapter.log(request, response, 0);
                error = true;
            }

            if (!error) {
                // Setting up filters, and parse some request headers
　　　　　　　　　 rp.setStage(org.apache.coyote.Constants.STAGE_ENDED);
　　　　　　　　　 try {
                    prepareRequest();//对请求内容增加过滤器——协议、方法、请求头、host等
                } catch (Throwable t) {
                    if (log.isDebugEnabled()) {
                        log.debug(sm.getString("http11processor.request.prepare"), t);
                    }
                    // 400 - Internal Server Error
                    response.setStatus(400);
                    adapter.log(request, response, 0);
                    error = true;
                }
            }

            if (maxKeepAliveRequests > 0 && keepAliveLeft == 0)
                keepAlive = false;
　　　　　　　 // Process the request in the adapter
            if (!error) {
                try {
                    rp.setStage(org.apache.coyote.Constants.STAGE_SERVICE);
                    adapter.service(request, response); //将进一步处理交给CoyoteAdapter
                    // 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 && !error) { // Avoid checking twice.
                        error = response.getErrorException() != null ||
                                statusDropsConnection(response.getStatus());
                    }

                } catch (InterruptedIOException e) {
                    error = true;
                } catch (Throwable t) {
                    log.error(sm.getString("http11processor.request.process"), t);
                    // 500 - Internal Server Error
                    response.setStatus(500);
                    adapter.log(request, response, 0);
                    error = true;
                }
            }

            // Finish the handling of the request
            try {
                rp.setStage(org.apache.coyote.Constants.STAGE_ENDINPUT);
                // If we know we are closing the connection, don't drain input.
                // This way uploading a 100GB file doesn't tie up the thread
                // if the servlet has rejected it.

                if(error && !async)
                    inputBuffer.setSwallowInput(false);
                if (!async)
                    endRequest();
            } catch (Throwable t) {
                log.error(sm.getString("http11processor.request.finish"), t);
                // 500 - Internal Server Error
                response.setStatus(500);
                adapter.log(request, response, 0);
                error = true;
            }
            try {
                rp.setStage(org.apache.coyote.Constants.STAGE_ENDOUTPUT);
            } catch (Throwable t) {
                log.error(sm.getString("http11processor.response.finish"), t);
                error = true;
            }

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

            rp.setStage(org.apache.coyote.Constants.STAGE_KEEPALIVE);

            // Don't reset the param - we'll see it as ended. Next request
            // will reset it
            // thrA.setParam(null);
            // Next request
            if (!async || error) {
                inputBuffer.nextRequest();
                outputBuffer.nextRequest();
            }

            //hack keep alive behavior
            break;
        }

        rp.setStage(org.apache.coyote.Constants.STAGE_ENDED);
        if (error) {
            recycle();
            return SocketState.CLOSED;
        } else if (async) {
            return SocketState.LONG;
        } else {
            if (!keepAlive) {
                recycle();
                return SocketState.CLOSED;
            } else {
                return SocketState.OPEN;
            }
        } 

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

    /**
     * Service method.
     */
    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().setQueryStringEncoding
                (connector.getURIEncoding());

        }

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

        boolean comet = false;
        boolean async = false;

        try {

            // Parse and set Catalina and configuration specific
            // request parameters
            req.getRequestProcessor().setWorkerThreadName(Thread.currentThread().getName());
            if (postParseRequest(req, request, res, response)) {
                //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.isComet()) {
                    if (!response.isClosed() && !response.isError()) {
                        if (request.getAvailable() || (request.getContentLength() > 0 && (!request.isParametersParsed()))) {
                            // Invoke a read event right away if there are available bytes
                            if (event(req, res, SocketStatus.OPEN)) {
                                comet = true;
                                res.action(ActionCode.ACTION_COMET_BEGIN, null);
                            }
                        } else {
                            comet = true;
                            res.action(ActionCode.ACTION_COMET_BEGIN, null);
                        }
                    } else {
                        // Clear the filter chain, as otherwise it will not be reset elsewhere
                        // since this is a Comet request
                        request.setFilterChain(null);
                    }
                }

            }
            AsyncContextImpl asyncConImpl = (AsyncContextImpl)request.getAsyncContext();
            if (asyncConImpl!=null && asyncConImpl.getState()==AsyncContextImpl.AsyncState.STARTED) {
                res.action(ActionCode.ACTION_ASYNC_START, request.getAsyncContext());
                async = true;
            } else if (request.isAsyncDispatching()) {
                asyncDispatch(req, res, SocketStatus.OPEN);
                if (request.isAsyncStarted()) {
                    async = true;
                    res.action(ActionCode.ACTION_ASYNC_START, request.getAsyncContext());
                }
            } else if (!comet) {
                response.finishResponse();
                req.action(ActionCode.ACTION_POST_REQUEST , null);
            }

        } catch (IOException e) {
            // Ignore
        } catch (Throwable t) {
            log.error(sm.getString("coyoteAdapter.service"), t);
        } finally {
            req.getRequestProcessor().setWorkerThreadName(null);
            // Recycle the wrapper request and response
            if (!comet && !async) {
                request.recycle();
                response.recycle();
            } else {
                // Clear converters so that the minimum amount of memory
                // is used by this processor
                request.clearEncoders();
                response.clearEncoders();
            }
        }

    }

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

    /**
     * Parse additional request parameters.
     */
    protected boolean postParseRequest(org.apache.coyote.Request req,
                                       Request request,
                                   org.apache.coyote.Response res,
                                       Response response)
            throws Exception {
//   省略前边的次要代码
        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;
        }

        // Set the remote principal
        String principal = req.getRemoteUser().toString();
        if (principal != null) {
            request.setUserPrincipal(new CoyotePrincipal(principal));
        }

        // Set the authorization type
        String authtype = req.getAuthType().toString();
        if (authtype != null) {
            request.setAuthType(authtype);
        }

        // Request mapping.
        MessageBytes serverName;
        if (connector.getUseIPVHosts()) {
            serverName = req.localName();
            if (serverName.isNull()) {
                // well, they did ask for it
                res.action(ActionCode.ACTION_REQ_LOCAL_NAME_ATTRIBUTE, null);
            }
        } else {
            serverName = req.serverName();
        }
        if (request.isAsyncStarted()) {
            //TODO SERVLET3 - async
            //reset mapping data, should prolly be done elsewhere
            request.getMappingData().recycle();
        }
        connector.getMapper().map(serverName, decodedURI,
                                  request.getMappingData());
        request.setContext((Context) request.getMappingData().context);
        request.setWrapper((Wrapper) request.getMappingData().wrapper);

        // 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;
        }

        // 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
        if (request.getServletContext().getEffectiveSessionTrackingModes()
                .contains(SessionTrackingMode.URL)) {

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

        // Possible redirect
        MessageBytes redirectPathMB = request.getMappingData().redirectPath;
        if (!redirectPathMB.isNull()) {
            String redirectPath = urlEncoder.encode(redirectPathMB.toString());
            String query = request.getQueryString();
            if (request.isRequestedSessionIdFromURL()) {
                // This is not optimal, but as this is not very common, it
                // shouldn't matter
                redirectPath = redirectPath + ";" +
                    ApplicationSessionCookieConfig.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;
        }

        // Finally look for session ID in cookies and SSL session
        parseSessionCookiesId(req, request);
        parseSessionSslId(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

    public void map(MessageBytes host, MessageBytes uri,
                    MappingData mappingData)
        throws Exception {

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