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(guò)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(tīng)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(kāi)始經(jīng)過(guò)的所有容器都含有責(zé)任鏈模式，每經(jīng)過(guò)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(tīng)用戶的請(qǐng)求，監(jiān)聽(tīng)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(xiě)事件，就執(zhí)行processSocket(attachment, SocketEvent.OPEN_WRITE, true);讀大于寫(xiě)。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(xiě)
// 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(xiě)
// 就對(duì)NioSocketWrapper進(jìn)行寫(xiě)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(méi)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(méi)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(xiě)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(xiě)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(kāi)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);
@Override
public 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(guò)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-OP
return 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(méi)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(méi)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(guò)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-used
release(processor);
// Create the upgrade processor
processor = upgradeProtocol.getProcessor(wrapper, getProtocol().getAdapter());
wrapper.unRead(leftOverInput);
// Associate with the processor with the connection
connections.put(socket, processor);
} else {
if (getLog().isDebugEnabled()) {
getLog().debug(sm.getString(
"abstractConnectionHandler.negotiatedProcessor.fail",
"h2c"));
}
// Exit loop and trigger appropriate clean-up
state = 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(guò)connector.getService()方法就可以拿到Service，然后從Service開(kāi)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(lái)就是從StandradEngine開(kāi)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(guò)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(méi)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(méi)有被初始化，就分配一個(gè)Servelt實(shí)例來(lái)處理request請(qǐng)求。
servlet = wrapper.allocate();
}
/// 省略代碼..........................................
// // 給該request創(chuàng)建Filter過(guò)濾鏈。Filter過(guò)濾鏈執(zhí)行完之后，會(huì)執(zhí)行Servelt
ApplicationFilterChain filterChain =
ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);
// Call the filter chain for this request
// NOTE: This also calls the servlet's service() method
try {
if ((servlet != null) && (filterChain != null)) {
// Swallow output if needed
if (context.getSwallowOutput()) {
try {
SystemLogHandler.startCapture();
if (request.isAsyncDispatching()) {
request.getAsyncContextInternal().doInternalDispatch();
} else {
// 調(diào)用過(guò)濾鏈
filterChain.doFilter(request.getRequest(),
response.getResponse());
}
/// 省略代碼..........................................
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