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);
@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-OP
return 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-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_UNАVAILABLE,
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_UNАVAILABLE,
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 {
// 调用过滤链
filterChain.doFilter(request.getRequest(),
response.getResponse());
}
/// 省略代码……………………………………
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