目錄

• 前言
• 一、EndPoint
• 二、ConnectionHandler
• 三、Coyote
• 四、容器責(zé)任鏈模式

前言

Tomcat最全UML類圖

Tomcat請(qǐng)求處理過程：

Connector對(duì)象創(chuàng)建的時(shí)候，會(huì)創(chuàng)建Http11NioProtocol的ProtocolHandler，在Connector的startInteral方法中，會(huì)啟動(dòng)AbstractProtocol，AbstractProtocol啟動(dòng)NioEndPoint進(jìn)行監(jiān)聽客戶端的請(qǐng)求，EndPoint接受到客戶端的請(qǐng)求之后，會(huì)交給Container去處理請(qǐng)求。請(qǐng)求從Engine開始經(jīng)過的所有容器都含有責(zé)任鏈模式，每經(jīng)過一個(gè)容器都會(huì)調(diào)用該容器的責(zé)任鏈對(duì)請(qǐng)求進(jìn)行處理。

一、EndPoint

默認(rèn)的EndPoint實(shí)現(xiàn)是NioEndPoint，NioEndPoint有四個(gè)內(nèi)部類，分別是Poller、Acceptor、PollerEvent、SocketProcessor、NioSocketWrapper。

（1）Acceptor負(fù)責(zé)監(jiān)聽用戶的請(qǐng)求，監(jiān)聽到用戶請(qǐng)求之后，調(diào)用getPoller0().register(channel);先將當(dāng)前請(qǐng)求封裝成PollerEvent，new PollerEvent(socket, ka, OP_REGISTER); 將當(dāng)前請(qǐng)求，封裝成注冊(cè)事件，并添加到PollerEvent隊(duì)列中，然后將PollerEvent注冊(cè)到Poller的Selector對(duì)象上面。

（2）Poller線程會(huì)一直遍歷可以處理的事件（netty的selestor），當(dāng)找到需要處理的事件之后，調(diào)用processKey(sk, socketWrapper);對(duì)，執(zhí)行要處理的PollerEvent的run方法，對(duì)請(qǐng)求進(jìn)行處理。

（3）PollerEvent繼承自Runnable接口，在其run方法里面,如果是PollerEvent的事件是注冊(cè)O(shè)P_REGISTER，那么就將當(dāng)前的socket注冊(cè)到Poller的selector上。

 public void run() {    if (interestOps == OP_REGISTER) {try {	// 核心代碼，終于找到了?。。。。?   // 當(dāng)事件是注冊(cè)的時(shí)候，將當(dāng)前的NioSocketChannel注冊(cè)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被取消的時(shí)候需要將SelectionKey對(duì)應(yīng)的EndPoint的Connection計(jì)數(shù)器，減一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線程內(nèi)會(huì)執(zhí)行keyCount = selector.select(selectorTimeout);獲取當(dāng)前需要處理的SelectionKey的數(shù)量，然后當(dāng)keyCount大于0時(shí)，會(huì)獲取selector的迭代器，遍歷所有需要的selectionkey，并對(duì)其進(jìn)行處理。在這里將socket的事件封裝成NioSocketWrapper。

// 得到selectedKeys的迭代器Iterator<SelectionKey> iterator = keyCount > 0 ? selector.selectedKeys().iterator() : null; // 遍歷所有的SelectionKey，并對(duì)其進(jìn)行處理 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，就處理     if (socketWrapper != null) { // 處理事件 processKey(sk, socketWrapper);     } }

processKey在處理SelectionKey，如果當(dāng)前Poller已經(jīng)關(guān)閉，就取消key。SelectionKey對(duì)應(yīng)的Channel如果發(fā)生讀事件，就調(diào)用AbatractEndPoint.processSocket執(zhí)行讀操作processSocket(attachment, SocketEvent.OPEN_READ, true)，如果SelectionKey對(duì)應(yīng)的Channel發(fā)生寫事件，就執(zhí)行processSocket(attachment, SocketEvent.OPEN_WRITE, true);讀大于寫。socket的事件處理調(diào)用的是AbatractEndPoint的processSocket方法。

protected void processKey(SelectionKey sk, NioSocketWrapper attachment) {	     try {	 if (close) {	     // 如果Poller已經(jīng)關(guān)閉了，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	     // 讀優(yōu)于寫	     // 如果SelectionKey對(duì)應(yīng)的Channel已經(jīng)準(zhǔn)備好了讀	     // 就對(duì)NioSocketWrapper進(jìn)行讀操作	     if (sk.isReadable()) {	 if (!processSocket(attachment, SocketEvent.OPEN_READ, true)) {	     closeSocket = true;	 }	     }	     // 如果SelectionKey對(duì)應(yīng)的Channel已經(jīng)準(zhǔn)備好了寫	     // 就對(duì)NioSocketWrapper進(jìn)行寫操作	     if (!closeSocket && sk.isWritable()) {	 if (!processSocket(attachment, SocketEvent.OPEN_WRITE, true)) {	     closeSocket = true;	 }	     }	     if (closeSocket) {	 // 如果已經(jīng)關(guān)閉了，就取消key	 cancelledKey(sk);	     }	 }	     }	     }

AbatractEndPoint.processSocket方法首先從緩存中獲取SocketProcessor類，如果緩存中沒有就創(chuàng)建一個(gè)，SocketProcessorBase接口對(duì)應(yīng)的就是NioEndPoint.SocketProcessor，也就是Worker。將對(duì)應(yīng)的SocketProcessor類放入到線程池中執(zhí)行。

 public boolean processSocket(SocketWrapperBase<S> socketWrapper, SocketEvent event, boolean dispatch) {	// 得到socket的處理器	// Connector在構(gòu)造函數(shù)里面已經(jīng)指定了協(xié)議：org.apache.coyote.http11.Http11NioProtocol。	SocketProcessorBase<S> sc = processorCache.pop();	if (sc == null) {	// 如果沒有，就創(chuàng)建一個(gè)Socket的處理器。創(chuàng)建的時(shí)候指定socketWrapper以及socket的事件。	    sc = createSocketProcessor(socketWrapper, event);	} else {	    sc.reset(socketWrapper, event);	}	//socket的處理交給了線程池去處理。	Executor executor = getExecutor();	if (dispatch && executor != null) {	    executor.execute(sc);	} else {	    sc.run();	}

（5）NioEndPoint.NioSocketWrapper，是Socket的封裝類，增強(qiáng)類，將Socket與其他對(duì)象建立關(guān)聯(lián)。

 public static class NioSocketWrapper extends SocketWrapperBase<NioChannel> { 		private final NioSelectorPool pool;private Poller poller = null; // 輪詢的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）繼承了Runnable接口，負(fù)責(zé)對(duì)socket的g各種事件進(jìn)行處理。讀事件、寫事件、停止時(shí)間、超時(shí)事件、斷連事件、錯(cuò)誤時(shí)間、連接失敗事件。

SocketProcessor的doRun方法，會(huì)根據(jù)SocketState進(jìn)行處理，SocketState 為STOP、DISCONNECT或者ERROR的時(shí)候就進(jìn)行關(guān)閉，SocketWrapperBase對(duì)應(yīng)的selector事件，得到指定的Handler處理器進(jìn)行處理。

@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()) {     // 是否已經(jīng)握手成功，不需要TLS(加密)握手，就讓處理器對(duì)socket和event的組合進(jìn)行處理。     handshake = 0; } else if (event == SocketEvent.STOP || event == SocketEvent.DISCONNECT || event == SocketEvent.ERROR) {     // 不能夠完成TLS握手，就把他認(rèn)為是TLS握手失敗。     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.     // 握手從/向socket讀/寫時(shí)，握手一旦完成狀態(tài)應(yīng)該為OPEN_WRITE，     // 握手是在套接字打開時(shí)發(fā)生的，因此在完成后狀態(tài)必須始終為OPEN_READ     // 始終設(shè)置此選項(xiàng)是可以的，因?yàn)樗鼉H在握手完成時(shí)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) { // 調(diào)用處理器進(jìn)行處理。 // NioEndPoint的默認(rèn)Handler是Http11的 // 這里的Handler是AbstractProtocol.ConnectionHandler // 這個(gè)Handler的設(shè)置方法是： // 首先在Connector類的構(gòu)造函數(shù)中，將默認(rèn)的ProtocolHandler設(shè)置為org.apache.coyote.http11.Http11NioProtocol // AbstractHttp11Protocol的構(gòu)造函數(shù)里面創(chuàng)建了Handler類ConnectionHandler state = getHandler().process(socketWrapper, SocketEvent.OPEN_READ);     } else { state = getHandler().process(socketWrapper, event);     }     // 如果返回的狀態(tài)是SocketState，那么就關(guān)掉連接     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，也就是讀事件的話，就將OP_READ時(shí)間設(shè)置到socketWrapper     socketWrapper.registerReadInterest(); } else if (handshake == SelectionKey.OP_WRITE) {     // 如果是SelectionKey.OP_WRITE，也就是讀事件的話，就將OP_WRITE事件設(shè)置到socketWrapper     socketWrapper.registerWriteInterest(); }

二、ConnectionHandler

（1）ConnectionHandler用于根據(jù)Socket連接找到相應(yīng)的Engine處理器。

上面是SocketProcessor的doRun方法，執(zhí)行了getHandler().process(socketWrapper, SocketEvent.OPEN_READ);;process方法是首先在Map緩存中查找當(dāng)前socket是否存在對(duì)應(yīng)的processor，如果不存在，再去可循環(huán)的處理器棧中查找是否存在，如果不存在就創(chuàng)建相應(yīng)的Processor，然后將新創(chuàng)建的Processor與Socket建立映射，存在connection的Map中。在任何一個(gè)階段得到Processor對(duì)象之后，會(huì)執(zhí)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);// 終于找到了這個(gè)集合，給Socket和處理器建立連接// 對(duì)每個(gè)有效鏈接都會(huì)緩存進(jìn)這里，用于連接選擇一個(gè)合適的Processor實(shí)現(xiàn)以進(jìn)行請(qǐng)求處理。private final Map<S, Processor> connections = new ConcurrentHashMap<>();// 可循環(huán)的處理器棧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已經(jīng)被關(guān)閉了，所以不需要做任何操作。return SocketState.CLOSED;    }    // 得到wrapper內(nèi)的Socket對(duì)象    S socket = wrapper.getSocket();    // 從Map緩沖區(qū)中得到socket對(duì)應(yīng)的處理器。    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.    // 超時(shí)是在專用線程上計(jì)算的，然后被調(diào)度。    // 因?yàn)檎{(diào)度過程中的延遲，可能不再需要超時(shí)。檢查這里，避免不必要的處理。    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緩存存在該socket相關(guān)的處理器    if (processor != null) {// Make sure an async timeout doesn"t fire// 確保沒有觸發(fā)異步超時(shí)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事件是關(guān)閉，或者SocketEvent時(shí)間出錯(cuò)，此時(shí)不需要做任何操作。// Endpoint需要一個(gè)CLOSED的信號(hào)，并且這里不再有與這個(gè)socket有關(guān)聯(lián)了return SocketState.CLOSED;    }    ContainerThreadMarker.set();    try {// Map緩存不存在該socket相關(guān)的處理器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通常在沒有協(xié)議協(xié)商時(shí)返回""    if (negotiatedProtocol != null && negotiatedProtocol.length() > 0) {// 獲取協(xié)商協(xié)議UpgradeProtocol upgradeProtocol = getProtocol().getNegotiatedProtocol(negotiatedProtocol);if (upgradeProtocol != null) {    // 升級(jí)協(xié)議為空    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));    */}    }}// 經(jīng)過上面的操作，processor還是null的話。if (processor == null) {    // 從recycledProcessors可循環(huán)processors中獲取processor    processor = recycledProcessors.pop();    if (getLog().isDebugEnabled()) {getLog().debug(sm.getString("abstractConnectionHandler.processorPop", processor));    }}if (processor == null) {    // 創(chuàng)建處理器    processor = getProtocol().createProcessor();    register(processor);    if (getLog().isDebugEnabled()) {getLog().debug(sm.getString("abstractConnectionHandler.processorCreate", processor));    }}processor.setSslSupport(wrapper.getSslSupport(getProtocol().getClientCertProvider()));// 將socket和processor建立關(guān)聯(lián)。connections.put(socket, processor);SocketState state = SocketState.CLOSED;do {    // 調(diào)用processor的process方法。    state = processor.process(wrapper, status);    // processor的process方法返回升級(jí)狀態(tài)    if (state == SocketState.UPGRADING) {// Get the HTTP upgrade handler// 得到HTTP的升級(jí)句柄UpgradeToken upgradeToken = processor.getUpgradeToken();// Retrieve leftover input// 檢索剩余輸入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協(xié)議為例，執(zhí)行的是Http11Processor，Http11Processor的祖父類AbstractProcessorLight實(shí)現(xiàn)了process方法，process調(diào)用了service模板方法，service模板方法是由Http11Processor進(jìn)行實(shí)現(xiàn)的。service方法最重要的操作是執(zhí)行getAdapter().service(request, response);

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

三、Coyote

回顧一下CoyoteAdapter的創(chuàng)建是在Connector的initInternal方法。

@Override    public SocketState service(SocketWrapperBase<?> socketWrapper)    throws IOException {		// 上面省略n行		// 調(diào)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轉(zhuǎn)成HttpServletRequest和HttpServletRsponse。然后，因?yàn)镃onnector在init的時(shí)候，將自己注入到了CoyoteAdapter中，所以，直接通過connector.getService()方法就可以拿到Service，然后從Service開始調(diào)用責(zé)任鏈模式，進(jìn)行處理。

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

四、容器責(zé)任鏈模式

接下來就是從StandradEngine開始的責(zé)任鏈模式。首先執(zhí)行StandradEngine的責(zé)任鏈模式，找到合適的Engine，合適的Engine在通過責(zé)任鏈模式找到合適的Context，直到找到StandardWrapperValve。最后執(zhí)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還沒有被初始化，就執(zhí)行初始化操作。如果是單線程模式就直接返回之前創(chuàng)建好的Servelt，如果是多線程模式，就先創(chuàng)建一個(gè)Servelt對(duì)象進(jìn)行返回。

@Override    public final void invoke(Request request, Response response)    throws IOException, ServletException {// 初始化我們需要的本地變量boolean unavailable = false;Throwable throwable = null;// This should be a Request attribute...long t1 = System.currentTimeMillis();// 原子類AtomicInteger，CAS操作，表示請(qǐng)求的數(shù)量。requestCount.incrementAndGet();StandardWrapper wrapper = (StandardWrapper) getContainer();Servlet servlet = null;Context context = (Context) wrapper.getParent();// 檢查當(dāng)前的Context應(yīng)用是否已經(jīng)被標(biāo)注為不可以使用if (!context.getState().isAvailable()) {    // 如果當(dāng)前應(yīng)用不可以使用的話，就報(bào)503錯(cuò)誤。    response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,    sm.getString("standardContext.isUnavailable"));    unavailable = true;}// 檢查Servelt是否被標(biāo)記為不可使用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是第一次調(diào)用的時(shí)候初始化try {    if (!unavailable) {// 如果此時(shí)Servelt還沒有被初始化，就分配一個(gè)Servelt實(shí)例來處理request請(qǐng)求。servlet = wrapper.allocate();    }/// 省略代碼..........................................// // 給該request創(chuàng)建Filter過濾鏈。Filter過濾鏈執(zhí)行完之后，會(huì)執(zhí)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 {    // 調(diào)用過濾鏈    filterChain.doFilter(request.getRequest(),    response.getResponse());}/// 省略代碼..........................................

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