Tomcat 核心组件 Connector

Connector是Tomcat的连接器，其主要任务是负责处理浏览器发送过来的请求，并创建一个Request和Response的对象用于和浏览器交换数据，然后产生一个线程用于处理请求，Connector会把Request和Response对象传递给该线程，该线程的具体的处理过程是Container容器的事了。执行过程分为以下几个步骤:

1. 实例化Connector，构造一个Connector对象。
2. 调用Connector的initIntenal方法，初始化Connetor。
3. 调用ProtocolHanlder的init方法，完成ProtocolHanlder的初始化。这个过程包括了创建线程池并创建一个线程处理浏览器请求。
4. 调用Connector的startIntenal方法，启动Connector。
5. 调用ProtocolHandler的start方法，启动Protocolhanlder。
6. 调用MapperListener的start方法，启动监听器程序。

Connect执行过程的时序图：

注意：由于Tomcat还支持AJP协议，但为了简化，我画的这个序列图是基于Http协议的，这也是我们在Web开发中接触最多的协议了。

在深入Connector之前我们先看看Connector类的结构：

既然是处理浏览器请求，那么需要支持http协议，在Tomcat中有两种协议处理器：HTTP/1.1与AJP/1.3协议处理器。在server.xml中已经指明tomcat所支持的两种协议：

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

在tomcat中是怎么样分别处理这两种协议的呢，我们可以ProtocolHanlder类中找到答案：

图中被选中的就是Tomcat默认使用协议处理器，其实现过程与Java标准Socket编程是一样的，在tomcat中可以使用Connetor类的setProtocol方法，看看源码就知道了：

    public void setProtocol(String protocol) {
        if (AprLifecycleListener.isAprAvailable()) {
            if ("HTTP/1.1".equals(protocol)) {
                setProtocolHandlerClassName
                    ("org.apache.coyote.http11.Http11AprProtocol");
            } else if ("AJP/1.3".equals(protocol)) {
                setProtocolHandlerClassName
                    ("org.apache.coyote.ajp.AjpAprProtocol");
            } else if (protocol != null) {
                setProtocolHandlerClassName(protocol);
            } else {
                setProtocolHandlerClassName
                    ("org.apache.coyote.http11.Http11AprProtocol");
            }
        } else {
            if ("HTTP/1.1".equals(protocol)) {
                setProtocolHandlerClassName
                    ("org.apache.coyote.http11.Http11Protocol");
            } else if ("AJP/1.3".equals(protocol)) {
                setProtocolHandlerClassName
                    ("org.apache.coyote.ajp.AjpProtocol");
            } else if (protocol != null) {
                setProtocolHandlerClassName(protocol);
            }
        }
    }

从第2个if子句的最后一个else可以知道tomcat默认使用的是http1.1协议。

我们再看看Connector的初始化过程：

    @Override
    protected void initInternal() throws LifecycleException {
        super.initInternal();
        // Initialize adapter
        adapter = new CoyoteAdapter(this);
        protocolHandler.setAdapter(adapter);
        // Make sure parseBodyMethodsSet has a default
        if( null == parseBodyMethodsSet ) {
            setParseBodyMethods(getParseBodyMethods());
        }
        if (protocolHandler.isAprRequired() &&
                !AprLifecycleListener.isAprAvailable()) {
            throw new LifecycleException(
                    sm.getString("coyoteConnector.protocolHandlerNoApr",
                            getProtocolHandlerClassName()));
        }
        try {
            protocolHandler.init();
        } catch (Exception e) {
            throw new LifecycleException
                (sm.getString
                 ("coyoteConnector.protocolHandlerInitializationFailed"), e);
        }
        // Initialize mapper listener
        mapperListener.init();
    }

从这段代码中可以看到：首先调用父类org.apache.catalina.util.LifecycleMBeanBase的初始化方法，然后创建一个Adapter，然后设置protocolHanlder（协议处理器）的Adapter，同时判断传过来的请求的请求方法（比如get或者post），如果没有指明请求方法，默认使用post处理，然后调用protocolHanlder的初始化方法，最后调用mapperListener的初始化方法，而mapperListener的初始化方法调用的是org.apache.catalina.util.LifecycleBase的init方法，我们重点关注protocolHanlder的初始化方法，具体是实现在AbstractProtocol抽象类中，其直接子类有AbstractAjpProtocol和AbstractHttp11Protocol，分别对应的是两种不同的处理协议，所以协议处理器的初始化方法是在其子抽象类（实现ProtocolHanlder接口的抽象类）来实现的，这里看看AbstractHttp11Protocol的初始化方法：

    @Override
    public void init() throws Exception {
        if (getLog().isInfoEnabled())
            getLog().info(sm.getString("abstractProtocolHandler.init",
                    getName()));
        if (oname == null) {
            // Component not pre-registered so register it
            oname = createObjectName();
            if (oname != null) {
                Registry.getRegistry(null, null).registerComponent(this, oname,
                    null);
            }
        }
        if (this.domain != null) {
            try {
                tpOname = new ObjectName(domain + ":" +
                        "type=ThreadPool,name=" + getName());
                Registry.getRegistry(null, null).registerComponent(endpoint,
                        tpOname, null);
            } catch (Exception e) {
                getLog().error(sm.getString(
                        "abstractProtocolHandler.mbeanRegistrationFailed",
                        tpOname, getName()), e);
            }
            rgOname=new ObjectName(domain +
                    ":type=GlobalRequestProcessor,name=" + getName());
            Registry.getRegistry(null, null).registerComponent(
                    getHandler().getGlobal(), rgOname, null );
        }
        String endpointName = getName();
        endpoint.setName(endpointName.substring(1, endpointName.length()-1));
        try {
            endpoint.init();
        } catch (Exception ex) {
            getLog().error(sm.getString("abstractProtocolHandler.initError",
                    getName()), ex);
            throw ex;
        }
    }

打断点调试可以知道oname的值是Tomcat:type=ProtocolHandler,port=auto-1,address=”127.0.0.1”,tpOname是Tomcat:type=ProtocolHandler,port=auto-1,address=”127.0.0.1”,rOname是Tomcat:type=GlobalRequestProcessor,name=”http-bio-127.0.0.1-auto-1”,我们重点关注endpoint的init方法，主要完成以下几个过程：

1. 设置线程接收数和最大连接数
2. 创建线程池,启动监听的线程监听用户请求
3. 启动一个线程处理请求

初始化完成Connector就可以启动了，启动阶段调用startInternal方法：

    @Override
    protected void startInternal() throws LifecycleException {
        // Validate settings before starting
        if (getPort() < 0) {
            throw new LifecycleException(sm.getString(
                    "coyoteConnector.invalidPort", Integer.valueOf(getPort())));
        }
        setState(LifecycleState.STARTING);
        try {
            protocolHandler.start();
        } catch (Exception e) {
            String errPrefix = "";
            if(this.service != null) {
                errPrefix += "service.getName(): \"" + this.service.getName() + "\"; ";
            }
            throw new LifecycleException
                (errPrefix + " " + sm.getString
                 ("coyoteConnector.protocolHandlerStartFailed"), e);
        }
        mapperListener.start();
    }

可以看出Connector调用protocolHandler.start()方法，继续看看这个方法的源码：

    @Override
    public void start() throws Exception {
        if (getLog().isInfoEnabled())
            getLog().info(sm.getString("abstractProtocolHandler.start",
                    getName()));
        try {
            endpoint.start();
        } catch (Exception ex) {
            getLog().error(sm.getString("abstractProtocolHandler.startError",
                    getName()), ex);
            throw ex;
        }
    }

这个方法又调用了endpoint.start()方法：

    public final void start() throws Exception {
        if (bindState == BindState.UNBOUND) {
            bind();
            bindState = BindState.BOUND_ON_START;
        }
        startInternal();
    }

然后又调用了org.apache.tomcat.util.net.AbstractEndpoint.startInternal()方法：

    @Override
    public void startInternal() throws Exception {
        if (!running) {
            running = true;
            paused = false;
            // Create worker collection
            if (getExecutor() == null) {
                createExecutor();
            }
            initializeConnectionLatch();
            startAcceptorThreads();
            // Start async timeout thread
            Thread timeoutThread = new Thread(new AsyncTimeout(),
                    getName() + "-AsyncTimeout");
            timeoutThread.setPriority(threadPriority);
            timeoutThread.setDaemon(true);
            timeoutThread.start();
        }
    }

1. 设置线程接收数和最大连接数
2. 创建线程池,启动监听的线程监听用户请求
3. 启动一个线程处理异步请求

这个异步线程是如何执行的呢？

    /**
     * Async timeout thread
     */
    protected class AsyncTimeout implements Runnable {
        /**
         * The background thread that checks async requests and fires the
         * timeout if there has been no activity.
         */
        @Override
        public void run() {
            // Loop until we receive a shutdown command
            while (running) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    // Ignore
                }
                long now = System.currentTimeMillis();
                Iterator<SocketWrapper<Socket>> sockets =
                    waitingRequests.iterator();
                while (sockets.hasNext()) {
                    SocketWrapper<Socket> socket = sockets.next();
                    long access = socket.getLastAccess();
                    if (socket.getTimeout() > 0 &&
                            (now-access)>socket.getTimeout()) {
                        processSocketAsync(socket,SocketStatus.TIMEOUT);
                    }
                }
                // Loop if endpoint is paused
                while (paused && running) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        // Ignore
                    }
                }
            }
        }
    }

    //processSocket
    public boolean processSocketAsync(SocketWrapper<Socket> socket,
            SocketStatus status) {
        try {
            synchronized (socket) {
                if (waitingRequests.remove(socket)) {
                    SocketProcessor proc = new SocketProcessor(socket,status);
                    ClassLoader loader = Thread.currentThread().getContextClassLoader();
                    try {
                        //threads should not be created by the webapp classloader
                        if (Constants.IS_SECURITY_ENABLED) {
                            PrivilegedAction<Void> pa = new PrivilegedSetTccl(
                                    getClass().getClassLoader());
                            AccessController.doPrivileged(pa);
                        } else {
                            Thread.currentThread().setContextClassLoader(
                                    getClass().getClassLoader());
                        }
                        // During shutdown, executor may be null - avoid NPE
                        if (!running) {
                            return false;
                        }
                        getExecutor().execute(proc);
                        //TODO gotta catch RejectedExecutionException and properly handle it
                    } finally {
                        if (Constants.IS_SECURITY_ENABLED) {
                            PrivilegedAction<Void> pa = new PrivilegedSetTccl(loader);
                            AccessController.doPrivileged(pa);
                        } else {
                            Thread.currentThread().setContextClassLoader(loader);
                        }
                    }
                }
            }
        } 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
            log.error(sm.getString("endpoint.process.fail"), t);
            return false;
        }
        return true;
    }

org.apache.tomcat.util.net.JIoEndpoint.SocketProcessor的职责是把具体的请求处理过程委派给org.apache.tomcat.util.net.JIoEndpoint.Handler，然后根据handler返回的不同SocketState，来决定是否关闭连接或者进行下一轮处理。

public void run() {
            boolean launch = false;
            synchronized (socket) {
                try {
                    SocketState state = SocketState.OPEN;
                    try {
                        // SSL handshake
                        serverSocketFactory.handshake(socket.getSocket());
                    } catch (Throwable t) {
                        ExceptionUtils.handleThrowable(t);
                        if (log.isDebugEnabled()) {
                            log.debug(sm.getString("endpoint.err.handshake"), t);
                        }
                        // Tell to close the socket
                        state = SocketState.CLOSED;
                    }
                    if ((state != SocketState.CLOSED)) {
                        if (status == null) {
                            state = handler.process(socket, SocketStatus.OPEN_READ);
                        } else {
                            state = handler.process(socket,status);
                        }
                    }
                    if (state == SocketState.CLOSED) {
                        // Close socket
                        if (log.isTraceEnabled()) {
                            log.trace("Closing socket:"+socket);
                        }
                        countDownConnection();
                        try {
                            socket.getSocket().close();
                        } catch (IOException e) {
                            // Ignore
                        }
                    } else if (state == SocketState.OPEN ||
                            state == SocketState.UPGRADING ||
                            state == SocketState.UPGRADING_TOMCAT  ||
                            state == SocketState.UPGRADED){
                        socket.setKeptAlive(true);
                        socket.access();
                        launch = true;
                    } else if (state == SocketState.LONG) {
                        socket.access();
                        waitingRequests.add(socket);
                    }
                } finally {
                    if (launch) {
                        try {
                            getExecutor().execute(new SocketProcessor(socket, SocketStatus.OPEN_READ));
                        } catch (RejectedExecutionException x) {
                            log.warn("Socket reprocessing request was rejected for:"+socket,x);
                            try {
                                //unable to handle connection at this time
                                handler.process(socket, SocketStatus.DISCONNECT);
                            } finally {
                                countDownConnection();
                            }
                        } catch (NullPointerException npe) {
                            if (running) {
                                log.error(sm.getString("endpoint.launch.fail"),
                                        npe);
                            }
                        }
                    }
                }
            }
            socket = null;
            // Finish up this request
        }
    }

其中的process方法主要完成对request的解析，包括请求头、请求行和请求体 ：

    //process method of org.apache.coyote.http11.AbstractHttp11Processor<S>.HttpProcessor extends org.apache.coyote.http11.AbstractHttp11Processor<S>
    @Override
    public SocketState process(SocketWrapper<S> socketWrapper)
        throws IOException {
        RequestInfo rp = request.getRequestProcessor();
        rp.setStage(org.apache.coyote.Constants.STAGE_PARSE);
        // Setting up the I/O
        setSocketWrapper(socketWrapper);
        getInputBuffer().init(socketWrapper, endpoint);
        getOutputBuffer().init(socketWrapper, endpoint);
        // Flags
        error = false;
        keepAlive = true;
        comet = false;
        openSocket = false;
        sendfileInProgress = false;
        readComplete = true;
        if (endpoint.getUsePolling()) {
            keptAlive = false;
        } else {
            keptAlive = socketWrapper.isKeptAlive();
        }
        if (disableKeepAlive()) {
            socketWrapper.setKeepAliveLeft(0);
        }
        while (!error && keepAlive && !comet && !isAsync() &&
                upgradeInbound == null &&
                httpUpgradeHandler == null && !endpoint.isPaused()) {
            // Parsing the request header
            try {
                setRequestLineReadTimeout();
                if (!getInputBuffer().parseRequestLine(keptAlive)) {
                    if (handleIncompleteRequestLineRead()) {
                        break;
                    }
                }
                if (endpoint.isPaused()) {
                    // 503 - Service unavailable
                    response.setStatus(503);
                    error = true;
                } else {
                    // Make sure that connectors that are non-blocking during
                    // header processing (NIO) only set the start time the first
                    // time a request is processed.
                    if (request.getStartTime() < 0) {
                        request.setStartTime(System.currentTimeMillis());
                    }
                    keptAlive = true;
                    // Set this every time in case limit has been changed via JMX
                    request.getMimeHeaders().setLimit(endpoint.getMaxHeaderCount());
                    // Currently only NIO will ever return false here
                    if (!getInputBuffer().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) {
                        setSocketTimeout(connectionUploadTimeout);
                    }
                }
            } catch (IOException e) {
                if (getLog().isDebugEnabled()) {
                    getLog().debug(
                            sm.getString("http11processor.header.parse"), e);
                }
                error = true;
                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:
                            getLog().info(message);
                            break;
                        case DEBUG:
                            getLog().debug(message);
                    }
                }
                // 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_PREPARE);
                try {
                    prepareRequest();
                } catch (Throwable t) {
                    ExceptionUtils.handleThrowable(t);
                    if (getLog().isDebugEnabled()) {
                        getLog().debug(sm.getString(
                                "http11processor.request.prepare"), t);
                    }
                    // 400 - Internal Server Error
                    response.setStatus(400);
                    adapter.log(request, response, 0);
                    error = true;
                }
            }
            if (maxKeepAliveRequests == 1) {
                keepAlive = false;
            } else if (maxKeepAliveRequests > 0 &&
                    socketWrapper.decrementKeepAlive() <= 0) {
                keepAlive = false;
            }
            // Process the request in the adapter
            if (!error) {
                try {
                    rp.setStage(org.apache.coyote.Constants.STAGE_SERVICE);
                    adapter.service(request, response);

                    if(keepAlive && !error) { // Avoid checking twice.
                        error = response.getErrorException() != null ||
                                (!isAsync() &&
                                statusDropsConnection(response.getStatus()));
                    }
                    setCometTimeouts(socketWrapper);
                } catch (InterruptedIOException e) {
                    error = true;
                } catch (HeadersTooLargeException e) {
                    error = true;
                    // The response should not have been committed but check it
                    // anyway to be safe
                    if (!response.isCommitted()) {
                        response.reset();
                        response.setStatus(500);
                        response.setHeader("Connection", "close");
                    }
                } catch (Throwable t) {
                    ExceptionUtils.handleThrowable(t);
                    getLog().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
            rp.setStage(org.apache.coyote.Constants.STAGE_ENDINPUT);
            if (!isAsync() && !comet) {
                if (error) {

                    getInputBuffer().setSwallowInput(false);
                }
                if (response.getStatus() < 200 || response.getStatus() > 299) {
                    if (expectation) {
                        // Client sent Expect: 100-continue but received a
                        // non-2xx response. Disable keep-alive (if enabled) to
                        // ensure the connection is closed. Some clients may
                        // still send the body, some may send the next request.
                        // No way to differentiate, so close the connection to
                        // force the client to send the next request.
                        getInputBuffer().setSwallowInput(false);
                        keepAlive = false;
                    }
                }
                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 (error) {
                response.setStatus(500);
            }
            request.updateCounters();
            if (!isAsync() && !comet || error) {
                getInputBuffer().nextRequest();
                getOutputBuffer().nextRequest();
            }
            if (!disableUploadTimeout) {
                if(endpoint.getSoTimeout() > 0) {
                    setSocketTimeout(endpoint.getSoTimeout());
                } else {
                    setSocketTimeout(0);
                }
            }
            rp.setStage(org.apache.coyote.Constants.STAGE_KEEPALIVE);
            if (breakKeepAliveLoop(socketWrapper)) {
                break;
            }
        }
        rp.setStage(org.apache.coyote.Constants.STAGE_ENDED);
        }
    }

首先在Http11Processor的process方法里，会先从socket里读取http请求数据，并解析请求头，构造Request对象和Response对象，然后调用Adapter.service()方法。Adapter.service()完成请求行以及请求体的解析，并把解析出来的信息封装到Request和Response对象中，Adapter（确切说是org.apache.catalina.connector.CoyoteAdapter）是connector和container的桥梁，经过这一步，请求就从connector传递到container里了，Adapter.service()方法之后便将封装了Request以及Response对象的Socket传给Container容器了。

要注意的是：最先处理请求的Request是org.apache.coyote.Request类型，这是一个Tomcat中一个轻量级对象，完成基本的请求处理后很容易被JVM回收，那为什么不直接交给Connector.Request对象处理呢？由于后者是Servlet容器真正传递的对象其完成的职责比前者复杂，这里使用org.apache.coyote.Request主要减轻后者的任务负担，出于性能考虑才这么设计。

具体service方法清单如下：

@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().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());
          //postParseRequest方法把CoyoteRequest转换为Connector.Request对象
          //后一类型的对象才是在Tomcat容器流转时真正传递的对象
          boolean postParseSuccess = postParseRequest(req, request, res, response);
          if (postParseSuccess) {
              //check valves if we support async
              request.setAsyncSupported(connector.getService().getContainer().getPipeline().isAsyncSupported());
    // 调用Container容器的invoke方法，把请求交给Container容器
              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_READ)) {
                              comet = true;
                              res.action(ActionCode.COMET_BEGIN, null);
                          }
                      } else {
                          comet = true;
                          res.action(ActionCode.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) {
              async = true;
          } else if (!comet) {
              request.finishRequest();
              response.finishResponse();
              if (postParseSuccess &&
                      request.getMappingData().context != null) {
                  ((Context) request.getMappingData().context).logAccess(
                          request, response,
                          System.currentTimeMillis() - req.getStartTime(),
                          false);
              }
              req.action(ActionCode.POST_REQUEST , null);
          }
      } catch (IOException e) {
          // Ignore
      } finally {
         //ignore
      }
  }

从connector.getService().getContainer().getPipeline().getFirst().invoke(request, response);这句代码中可以知道下一步的处理需要交给Container容器了。

经过上面一系列复杂的操作流程，Tomcat的Connector已经完成了protocol.start()方法，返回Connector的startIntenal方法，还有一个步骤要完成就是mapperListener.start()的方法了，整个执行过程比较简单，有两步：

1. 执行Connector的startIntenal方法
2. 执行MapperListener的startIntenal方法

   @Override
    public void startInternal() throws LifecycleException {
        setState(LifecycleState.STARTING);
        findDefaultHost();
        Engine engine = (Engine) connector.getService().getContainer();
        addListeners(engine);
        Container[] conHosts = engine.findChildren();
        for (Container conHost : conHosts) {
            Host host = (Host) conHost;
            if (!LifecycleState.NEW.equals(host.getState())) {
                // Registering the host will register the context and wrappers
                registerHost(host);
            }
        }
    }

首先注册已初始化的组件，然后为这些组件添加监听器，最后添加容器之间的映射关系。

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原文博主地址：rhwayfunn