Tomcat源码解析之Web请求与处理

目录

• 前言
• 一、EndPoint
• 二、ConnectionHandler
• 三、Coyote
• 四、容器责任链模式

前言

Tomcat最全UML类图

Tomcat请求处理过程：

Connector对象创建的时候，会创建Http11NioProtocol的ProtocolHandler，在Connector的startInteral方法中，会启动AbstractProtocol，AbstractProtocol启动NioEndPoint进行监听客户端的请求，EndPoint接受到客户端的请求之后，会交给Container去处理请求。请求从Engine开始经过的所有容器都含有责任链模式，每经过一个容器都会调用该容器的责任链对请求进行处理。

一、EndPoint

默认的EndPoint实现是NioEndPoint，NioEndPoint有四个内部类，分别是Poller、Acceptor、PollerEvent、SocketProcessor、NioSocketWrapper。

（1）Acceptor负责监听用户的请求，监听到用户请求之后，调用getPoller0().register(channel);先将当前请求封装成PollerEvent，new PollerEvent(socket, ka, OP_REGISTER); 将当前请求，封装成注册事件，并添加到PollerEvent队列中，然后将PollerEvent注册到Poller的Selector对象上面。

（2）Poller线程会一直遍历可以处理的事件（netty的selestor），当找到需要处理的事件之后，调用processKey(sk, socketWrapper);对，执行要处理的PollerEvent的run方法，对请求进行处理。

（3）PollerEvent继承自Runnable接口，在其run方法里面,如果是PollerEvent的事件是注册OP_REGISTER，那么就将当前的socket注册到Poller的selector上。

 public void run() {    if (interestOps == OP_REGISTER) {try {	// 核心代码，终于找到了！！！！！    // 当事件是注册的时候，将当前的NioSocketChannel注册到Poller的Selector上。    socket.getIOChannel().register(    socket.getPoller().getSelector(), SelectionKey.OP_READ, socketWrapper);} catch (Exception x) {    log.error(sm.getString("endpoint.nio.registerFail"), x);}    } else {final SelectionKey key = socket.getIOChannel().keyFor(socket.getPoller().getSelector());try {    if (key == null) {// The key was cancelled (e.g. due to socket closure)// and removed from the selector while it was being// processed. Count down the connections at this point// since it won"t have been counted down when the socket// closed.// SelectionKey被取消的时候需要将SelectionKey对应的EndPoint的Connection计数器，减一socket.socketWrapper.getEndpoint().countDownConnection();((NioSocketWrapper) socket.socketWrapper).closed = true;    } else {final NioSocketWrapper socketWrapper = (NioSocketWrapper) key.attachment();if (socketWrapper != null) {    //we are registering the key to start with, reset the fairness counter.    int ops = key.interestOps() | interestOps;    socketWrapper.interestOps(ops);    key.interestOps(ops);} else {    socket.getPoller().cancelledKey(key);}    }} catch (CancelledKeyException ckx) {    try {socket.getPoller().cancelledKey(key);    } catch (Exception ignore) {    }}    }}

（4）Poller线程内会执行keyCount = selector.select(selectorTimeout);获取当前需要处理的SelectionKey的数量，然后当keyCount大于0时，会获取selector的迭代器，遍历所有需要的selectionkey，并对其进行处理。在这里将socket的事件封装成NioSocketWrapper。

// 得到selectedKeys的迭代器Iterator<SelectionKey> iterator = keyCount > 0 ? selector.selectedKeys().iterator() : null; // 遍历所有的SelectionKey，并对其进行处理 while (iterator != null && iterator.hasNext()) {     SelectionKey sk = iterator.next();     iterator.remove();     NioSocketWrapper socketWrapper = (NioSocketWrapper) sk.attachment();     // Attachment may be null if another thread has called     // cancelledKey()     // 如果有attachment，就处理     if (socketWrapper != null) { // 处理事件 processKey(sk, socketWrapper);     } }

processKey在处理SelectionKey，如果当前Poller已经关闭，就取消key。SelectionKey对应的Channel如果发生读事件，就调用AbatractEndPoint.processSocket执行读操作processSocket(attachment, SocketEvent.OPEN_READ, true)，如果SelectionKey对应的Channel发生写事件，就执行processSocket(attachment, SocketEvent.OPEN_WRITE, true);读大于写。socket的事件处理调用的是AbatractEndPoint的processSocket方法。

protected void processKey(SelectionKey sk, NioSocketWrapper attachment) {	     try {	 if (close) {	     // 如果Poller已经关闭了，就取消key	     cancelledKey(sk);	 } else if (sk.isValid() && attachment != null) {	     if (sk.isReadable() || sk.isWritable()) {	 if (attachment.getSendfileData() != null) {	     processSendfile(sk, attachment, false);	 } else {	     unreg(sk, attachment, sk.readyOps());	     boolean closeSocket = false;	     // Read goes before write	     // 读优于写	     // 如果SelectionKey对应的Channel已经准备好了读	     // 就对NioSocketWrapper进行读操作	     if (sk.isReadable()) {	 if (!processSocket(attachment, SocketEvent.OPEN_READ, true)) {	     closeSocket = true;	 }	     }	     // 如果SelectionKey对应的Channel已经准备好了写	     // 就对NioSocketWrapper进行写操作	     if (!closeSocket && sk.isWritable()) {	 if (!processSocket(attachment, SocketEvent.OPEN_WRITE, true)) {	     closeSocket = true;	 }	     }	     if (closeSocket) {	 // 如果已经关闭了，就取消key	 cancelledKey(sk);	     }	 }	     }	     }

AbatractEndPoint.processSocket方法首先从缓存中获取SocketProcessor类，如果缓存中没有就创建一个，SocketProcessorBase接口对应的就是NioEndPoint.SocketProcessor，也就是Worker。将对应的SocketProcessor类放入到线程池中执行。

 public boolean processSocket(SocketWrapperBase<S> socketWrapper, SocketEvent event, boolean dispatch) {	// 得到socket的处理器	// Connector在构造函数里面已经指定了协议：org.apache.coyote.http11.Http11NioProtocol。	SocketProcessorBase<S> sc = processorCache.pop();	if (sc == null) {	// 如果没有，就创建一个Socket的处理器。创建的时候指定socketWrapper以及socket的事件。	    sc = createSocketProcessor(socketWrapper, event);	} else {	    sc.reset(socketWrapper, event);	}	//socket的处理交给了线程池去处理。	Executor executor = getExecutor();	if (dispatch && executor != null) {	    executor.execute(sc);	} else {	    sc.run();	}

（5）NioEndPoint.NioSocketWrapper，是Socket的封装类，增强类，将Socket与其他对象建立关联。

 public static class NioSocketWrapper extends SocketWrapperBase<NioChannel> { 		private final NioSelectorPool pool;private Poller poller = null; // 轮询的Poller private int interestOps = 0;private CountDownLatch readLatch = null;private CountDownLatch writeLatch = null;private volatile SendfileData sendfileData = null;private volatile long lastRead = System.currentTimeMillis();private volatile long lastWrite = lastRead;private volatile boolean closed = false;

（6）NioEndPoint.SocketProcessor（Worker）继承了Runnable接口，负责对socket的g各种事件进行处理。读事件、写事件、停止时间、超时事件、断连事件、错误时间、连接失败事件。

SocketProcessor的doRun方法，会根据SocketState进行处理，SocketState 为STOP、DISCONNECT或者ERROR的时候就进行关闭，SocketWrapperBase对应的selector事件，得到指定的Handler处理器进行处理。

@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()) {     // 是否已经握手成功，不需要TLS(加密)握手，就让处理器对socket和event的组合进行处理。     handshake = 0; } else if (event == SocketEvent.STOP || event == SocketEvent.DISCONNECT || event == SocketEvent.ERROR) {     // 不能够完成TLS握手，就把他认为是TLS握手失败。     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.     // 握手从/向socket读/写时，握手一旦完成状态应该为OPEN_WRITE，     // 握手是在套接字打开时发生的，因此在完成后状态必须始终为OPEN_READ     // 始终设置此选项是可以的，因为它仅在握手完成时使用。     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) { // 调用处理器进行处理。 // NioEndPoint的默认Handler是Http11的 // 这里的Handler是AbstractProtocol.ConnectionHandler // 这个Handler的设置方法是： // 首先在Connector类的构造函数中，将默认的ProtocolHandler设置为org.apache.coyote.http11.Http11NioProtocol // AbstractHttp11Protocol的构造函数里面创建了Handler类ConnectionHandler state = getHandler().process(socketWrapper, SocketEvent.OPEN_READ);     } else { state = getHandler().process(socketWrapper, event);     }     // 如果返回的状态是SocketState，那么就关掉连接     if (state == SocketState.CLOSED) { close(socket, key);     } } else if (handshake == -1) {     getHandler().process(socketWrapper, SocketEvent.CONNECT_FAIL);     close(socket, key); } else if (handshake == SelectionKey.OP_READ) {     // 如果是SelectionKey.OP_READ，也就是读事件的话，就将OP_READ时间设置到socketWrapper     socketWrapper.registerReadInterest(); } else if (handshake == SelectionKey.OP_WRITE) {     // 如果是SelectionKey.OP_WRITE，也就是读事件的话，就将OP_WRITE事件设置到socketWrapper     socketWrapper.registerWriteInterest(); }

二、ConnectionHandler

（1）ConnectionHandler用于根据Socket连接找到相应的Engine处理器。

上面是SocketProcessor的doRun方法，执行了getHandler().process(socketWrapper, SocketEvent.OPEN_READ);;process方法是首先在Map缓存中查找当前socket是否存在对应的processor，如果不存在，再去可循环的处理器栈中查找是否存在，如果不存在就创建相应的Processor，然后将新创建的Processor与Socket建立映射，存在connection的Map中。在任何一个阶段得到Processor对象之后，会执行processor的process方法state = processor.process(wrapper, status);

protected static class ConnectionHandler<S> implements AbstractEndpoint.Handler<S> {private final AbstractProtocol<S> proto;private final RequestGroupInfo global = new RequestGroupInfo();private final AtomicLong registerCount = new AtomicLong(0);// 终于找到了这个集合，给Socket和处理器建立连接// 对每个有效链接都会缓存进这里，用于连接选择一个合适的Processor实现以进行请求处理。private final Map<S, Processor> connections = new ConcurrentHashMap<>();// 可循环的处理器栈private final RecycledProcessors recycledProcessors = new RecycledProcessors(this);		  		@Overridepublic SocketState process(SocketWrapperBase<S> wrapper, SocketEvent status) {    if (getLog().isDebugEnabled()) {getLog().debug(sm.getString("abstractConnectionHandler.process",wrapper.getSocket(), status));    }    if (wrapper == null) {// wrapper == null 表示Socket已经被关闭了，所以不需要做任何操作。return SocketState.CLOSED;    }    // 得到wrapper内的Socket对象    S socket = wrapper.getSocket();    // 从Map缓冲区中得到socket对应的处理器。    Processor processor = connections.get(socket);    if (getLog().isDebugEnabled()) {getLog().debug(sm.getString("abstractConnectionHandler.connectionsGet",processor, socket));    }    // Timeouts are calculated on a dedicated thread and then    // dispatched. Because of delays in the dispatch process, the    // timeout may no longer be required. Check here and avoid    // unnecessary processing.    // 超时是在专用线程上计算的，然后被调度。    // 因为调度过程中的延迟，可能不再需要超时。检查这里，避免不必要的处理。    if (SocketEvent.TIMEOUT == status &&    (processor == null ||    !processor.isAsync() && !processor.isUpgrade() ||    processor.isAsync() && !processor.checkAsyncTimeoutGeneration())) {// This is effectively a NO-OPreturn SocketState.OPEN;    }    // 如果Map缓存存在该socket相关的处理器    if (processor != null) {// Make sure an async timeout doesn"t fire// 确保没有触发异步超时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.// SocketEvent事件是关闭，或者SocketEvent时间出错，此时不需要做任何操作。// Endpoint需要一个CLOSED的信号，并且这里不再有与这个socket有关联了return SocketState.CLOSED;    }    ContainerThreadMarker.set();    try {// Map缓存不存在该socket相关的处理器if (processor == null) {    String negotiatedProtocol = wrapper.getNegotiatedProtocol();    // OpenSSL typically returns null whereas JSSE typically    // returns "" when no protocol is negotiated    // OpenSSL通常返回null，而JSSE通常在没有协议协商时返回""    if (negotiatedProtocol != null && negotiatedProtocol.length() > 0) {// 获取协商协议UpgradeProtocol upgradeProtocol = getProtocol().getNegotiatedProtocol(negotiatedProtocol);if (upgradeProtocol != null) {    // 升级协议为空    processor = upgradeProtocol.getProcessor(wrapper, getProtocol().getAdapter());    if (getLog().isDebugEnabled()) {getLog().debug(sm.getString("abstractConnectionHandler.processorCreate", processor));    }} 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));    */}    }}// 经过上面的操作，processor还是null的话。if (processor == null) {    // 从recycledProcessors可循环processors中获取processor    processor = recycledProcessors.pop();    if (getLog().isDebugEnabled()) {getLog().debug(sm.getString("abstractConnectionHandler.processorPop", processor));    }}if (processor == null) {    // 创建处理器    processor = getProtocol().createProcessor();    register(processor);    if (getLog().isDebugEnabled()) {getLog().debug(sm.getString("abstractConnectionHandler.processorCreate", processor));    }}processor.setSslSupport(wrapper.getSslSupport(getProtocol().getClientCertProvider()));// 将socket和processor建立关联。connections.put(socket, processor);SocketState state = SocketState.CLOSED;do {    // 调用processor的process方法。    state = processor.process(wrapper, status);    // processor的process方法返回升级状态    if (state == SocketState.UPGRADING) {// Get the HTTP upgrade handler// 得到HTTP的升级句柄UpgradeToken upgradeToken = processor.getUpgradeToken();// Retrieve leftover input// 检索剩余输入ByteBuffer leftOverInput = processor.getLeftoverInput();if (upgradeToken == null) {    // Assume direct HTTP/2 connection    UpgradeProtocol upgradeProtocol = getProtocol().getUpgradeProtocol("h2c");    if (upgradeProtocol != null) {// Release the Http11 processor to be re-usedrelease(processor);// Create the upgrade processorprocessor = upgradeProtocol.getProcessor(wrapper, getProtocol().getAdapter());wrapper.unRead(leftOverInput);// Associate with the processor with the connectionconnections.put(socket, processor);    } else {if (getLog().isDebugEnabled()) {    getLog().debug(sm.getString(    "abstractConnectionHandler.negotiatedProcessor.fail",    "h2c"));}// Exit loop and trigger appropriate clean-upstate = 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);    // 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);	

（2）以Http11协议为例，执行的是Http11Processor，Http11Processor的祖父类AbstractProcessorLight实现了process方法，process调用了service模板方法，service模板方法是由Http11Processor进行实现的。service方法最重要的操作是执行getAdapter().service(request, response);

@Override    public SocketState service(SocketWrapperBase<?> socketWrapper)    throws IOException {		// 上面省略n行		// 调用Coyote的service方法		 getAdapter().service(request, response);		 // 下面省略n行

三、Coyote

回顾一下CoyoteAdapter的创建是在Connector的initInternal方法。

@Override    public SocketState service(SocketWrapperBase<?> socketWrapper)    throws IOException {		// 上面省略n行		// 调用Coyote的service方法		 getAdapter().service(request, response);		 // 下面省略n行

Coyote的作用就是coyote.Request和coyote.Rsponse转成HttpServletRequest和HttpServletRsponse。然后，因为Connector在init的时候，将自己注入到了CoyoteAdapter中，所以，直接通过connector.getService()方法就可以拿到Service，然后从Service开始调用责任链模式，进行处理。

@Override    public SocketState service(SocketWrapperBase<?> socketWrapper)    throws IOException {		// 上面省略n行		// 调用Coyote的service方法		 getAdapter().service(request, response);		 // 下面省略n行

四、容器责任链模式

接下来就是从StandradEngine开始的责任链模式。首先执行StandradEngine的责任链模式，找到合适的Engine，合适的Engine在通过责任链模式找到合适的Context，直到找到StandardWrapperValve。最后执行到StandardWrapperValve的invoke方法。首先查看Context和Wrapper是不是不可用了，如果可用，并且Servelt还没有被初始化，就执行初始化操作。如果是单线程模式就直接返回之前创建好的Servelt，如果是多线程模式，就先创建一个Servelt对象进行返回。

@Override    public final void invoke(Request request, Response response)    throws IOException, ServletException {// 初始化我们需要的本地变量boolean unavailable = false;Throwable throwable = null;// This should be a Request attribute...long t1 = System.currentTimeMillis();// 原子类AtomicInteger，CAS操作，表示请求的数量。requestCount.incrementAndGet();StandardWrapper wrapper = (StandardWrapper) getContainer();Servlet servlet = null;Context context = (Context) wrapper.getParent();// 检查当前的Context应用是否已经被标注为不可以使用if (!context.getState().isAvailable()) {    // 如果当前应用不可以使用的话，就报503错误。    response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,    sm.getString("standardContext.isUnavailable"));    unavailable = true;}// 检查Servelt是否被标记为不可使用if (!unavailable && wrapper.isUnavailable()) {    container.getLogger().info(sm.getString("standardWrapper.isUnavailable",    wrapper.getName()));    long available = wrapper.getAvailable();    if ((available > 0L) && (available < Long.MAX_VALUE)) {response.setDateHeader("Retry-After", available);response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,sm.getString("standardWrapper.isUnavailable",wrapper.getName()));    } else if (available == Long.MAX_VALUE) {response.sendError(HttpServletResponse.SC_NOT_FOUND,sm.getString("standardWrapper.notFound",wrapper.getName()));    }    unavailable = true;}// Servelt是第一次调用的时候初始化try {    if (!unavailable) {// 如果此时Servelt还没有被初始化，就分配一个Servelt实例来处理request请求。servlet = wrapper.allocate();    }/// 省略代码..........................................// // 给该request创建Filter过滤链。Filter过滤链执行完之后，会执行ServeltApplicationFilterChain filterChain =ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);// Call the filter chain for this request// NOTE: This also calls the servlet"s service() methodtry {    if ((servlet != null) && (filterChain != null)) {// Swallow output if neededif (context.getSwallowOutput()) {    try {SystemLogHandler.startCapture();if (request.isAsyncDispatching()) {    request.getAsyncContextInternal().doInternalDispatch();} else {    // 调用过滤链    filterChain.doFilter(request.getRequest(),    response.getResponse());}/// 省略代码..........................................

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