从连接器（Connector）源码说起
既然是来解析连接器（Connector），那么我们直接从源码入手，后面所有源码我会剔除不重要部分，所以会忽略大部分源码细节，只关注流程。源码如下（高能预警，大量代码）：
public class Connector extends LifecycleMBeanBase {
public Connector() {
this("org.apache.coyote.http11.Http11NioProtocol");
}
public Connector(String protocol) {
boolean aprConnector = AprLifecycleListener.isAprAvailable() &&
AprLifecycleListener.getUseAprConnector();
if ("HTTP/1.1".equals(protocol) || protocol == null) {
if (aprConnector) {
protocolHandlerClassName = "org.apache.coyote.http11.Http11AprProtocol";
} else {
protocolHandlerClassName = "org.apache.coyote.http11.Http11NioProtocol";
}
} else if ("AJP/1.3".equals(protocol)) {
if (aprConnector) {
protocolHandlerClassName = "org.apache.coyote.ajp.AjpAprProtocol";
} else {
protocolHandlerClassName = "org.apache.coyote.ajp.AjpNioProtocol";
}
} else {
protocolHandlerClassName = protocol;
}
// Instantiate protocol handler
ProtocolHandler p = null;
try {
Class<?> clazz = Class.forName(protocolHandlerClassName);
p = (ProtocolHandler) clazz.getConstructor().newInstance();
} catch (Exception e) {
log.error(sm.getString(
"coyoteConnector.protocolHandlerInstantiationFailed"), e);
} finally {
this.protocolHandler = p;
}
// Default for Connector depends on this system property
setThrowOnFailure(Boolean.getBoolean("org.apache.catalina.startup.EXIT_ON_INIT_FAILURE"));
}
我们来看看Connector的构造方法，其实只做了一件事情，就是根据协议设置对应的ProtocolHandler,根据名称我们知道，这是协议处理类，所以连接器内部的一个重要子模块就是ProtocolHandler。
关于生命周期
我们看到Connector继承了LifecycleMBeanBase，我们来看看Connector的最终继承关系：
我们看到最终实现的是Lifecycle接口,我们看看这个接口是何方神圣。我把其接口的注释拿下来解释下
/**
* Common interface for component life cycle methods. Catalina components
* may implement this interface (as well as the appropriate interface(s) for
* the functionality they support) in order to provide a consistent mechanism
* to start and stop the component.
* start()
* -----------------------------
* | |
* | init() |
* NEW -»-- INITIALIZING |
* | | | | ------------------«-----------------------
* | | |auto | | |
* | | \|/ start() \|/ \|/ auto auto stop() |
* | | INITIALIZED --»-- STARTING_PREP --»- STARTING --»- STARTED --»--- |
* | | | | |
* | |destroy()| | |
* | --»-----«-- ------------------------«-------------------------------- ^
* | | | |
* | | \|/ auto auto start() |
* | | STOPPING_PREP ----»---- STOPPING ------»----- STOPPED -----»-----
* | \|/ ^ | ^
* | | stop() | | |
* | | -------------------------- | |
* | | | | |
* | | | destroy() destroy() | |
* | | FAILED ----»------ DESTROYING ---«----------------- |
* | | ^ | |
* | | destroy() | |auto |
* | --------»----------------- \|/ |
* | DESTROYED |
* | |
* | stop() |
* ----»-----------------------------»------------------------------
*
* Any state can transition to FAILED.
*
* Calling start() while a component is in states STARTING_PREP, STARTING or
* STARTED has no effect.
*
* Calling start() while a component is in state NEW will cause init() to be
* called immediately after the start() method is entered.
*
* Calling stop() while a component is in states STOPPING_PREP, STOPPING or
* STOPPED has no effect.
*
* Calling stop() while a component is in state NEW transitions the component
* to STOPPED. This is typically encountered when a component fails to start and
* does not start all its sub-components. When the component is stopped, it will
* try to stop all sub-components - even those it didn't start.
*
* Attempting any other transition will throw {@link LifecycleException}.
*
* </pre>
* The {@link LifecycleEvent}s fired during state changes are defined in the
* methods that trigger the changed. No {@link LifecycleEvent}s are fired if the
* attempted transition is not valid.
这段注释翻译就是，这个接口是提供给组件声明周期管理的，并且提供了声明周期流转图。这里我们只需要知道正常流程即可：
从生命周期探索连接器
根据上面的生命周期说明，我们可以知道连接器（Connector）就是按照如此的声明周期管理的，所以我们找到了线索，所以连接器肯定会先初始化然后再启动。我们查看其initInternal()方法可以知道连接器初始化做了什么事情，源码如下：
@Override
protected void initInternal() throws LifecycleException {
super.initInternal();
if (protocolHandler == null) {
throw new LifecycleException(
sm.getString("coyoteConnector.protocolHandlerInstantiationFailed"));
}
// Initialize adapter
adapter = new CoyoteAdapter(this);
protocolHandler.setAdapter(adapter);
if (service != null) {
protocolHandler.setUtilityExecutor(service.getServer().getUtilityExecutor());
}
// Make sure parseBodyMethodsSet has a default
if (null == parseBodyMethodsSet) {
setParseBodyMethods(getParseBodyMethods());
}
if (protocolHandler.isAprRequired() && !AprLifecycleListener.isInstanceCreated()) {
throw new LifecycleException(sm.getString("coyoteConnector.protocolHandlerNoAprListener",
getProtocolHandlerClassName()));
}
if (protocolHandler.isAprRequired() && !AprLifecycleListener.isAprAvailable()) {
throw new LifecycleException(sm.getString("coyoteConnector.protocolHandlerNoAprLibrary",
getProtocolHandlerClassName()));
}
if (AprLifecycleListener.isAprAvailable() && AprLifecycleListener.getUseOpenSSL() &&
protocolHandler instanceof AbstractHttp11JsseProtocol) {
AbstractHttp11JsseProtocol<?> jsseProtocolHandler =
(AbstractHttp11JsseProtocol<?>) protocolHandler;
if (jsseProtocolHandler.isSSLEnabled() &&
jsseProtocolHandler.getSslImplementationName() == null) {
// OpenSSL is compatible with the JSSE configuration, so use it if APR is available
jsseProtocolHandler.setSslImplementationName(OpenSSLImplementation.class.getName());
}
}
try {
protocolHandler.init();
} catch (Exception e) {
throw new LifecycleException(
sm.getString("coyoteConnector.protocolHandlerInitializationFailed"), e);
}
}
}
根据上面源码，我们发现主要是处理protocolHandler并初始化它，同时我们注意到了protocolHandler 设置了一个适配器，我们看看这个适配器是做啥的，跟踪源码如下：
/**
* The adapter, used to call the connector.
*
* @param adapter The adapter to associate
*/
public void setAdapter(Adapter adapter);
这个注释已经说的很直白了，这个适配器就是用来调用连接器的。我们再继续看看protocolHandler的初始化方法
/**
* Endpoint that provides low-level network I/O - must be matched to the
* ProtocolHandler implementation (ProtocolHandler using NIO, requires NIO
* Endpoint etc.).
*/
private final AbstractEndpoint<S,?> endpoint;
public void init() throws Exception {
if (getLog().isInfoEnabled()) {
getLog().info(sm.getString("abstractProtocolHandler.init", getName()));
logPortOffset();
}
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) {
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));
endpoint.setDomain(domain);
endpoint.init();
}
这里出现了一个新的对象，endpoint,根据注释我们可以知道endpoint是用来处理网络IO的，而且必须匹配到指定的子类（比如Nio,就是NioEndPoint处理）。endpoint.init()实际上就是做一些网络的配置，然后就是初始化完毕了。根据我们上面的周期管理，我们知道init()后就是start(),所以我们查看Connector的start()源码：
protected void startInternal() throws LifecycleException {
// Validate settings before starting
if (getPortWithOffset() < 0) {
throw new LifecycleException(sm.getString(
"coyoteConnector.invalidPort", Integer.valueOf(getPortWithOffset())));
}
setState(LifecycleState.STARTING);
try {
protocolHandler.start();
} catch (Exception e) {
throw new LifecycleException(
sm.getString("coyoteConnector.protocolHandlerStartFailed"), e);
}
}
其实就是主要调用 protocolHandler.start()方法，继续跟踪，为了方便表述，我会把接下来的代码统一放在一起说明，代码如下：
//1.类：AbstractProtocol implements ProtocolHandler,
MBeanRegistration
public void start() throws Exception {
// 省略部分代码
endpoint.start();
}
//2. 类：AbstractEndPoint
public final void start() throws Exception {
// 省略部分代码
startInternal();
}
/**3.类：NioEndPoint extends AbstractJsseEndpoint<NioChannel,SocketChannel>
* Start the NIO endpoint, creating acceptor, poller threads.
*/
@Override
public void startInternal() throws Exception {
//省略部分代码
// Start poller thread
poller = new Poller();
Thread pollerThread = new Thread(poller, getName() + "-ClientPoller");
pollerThread.setPriority(threadPriority);
pollerThread.setDaemon(true);
pollerThread.start();
startAcceptorThread();
}
}
到这里，其实整个启动代码就完成了，我们看到最后是在NioEndPoint创建了一个Poller,并且启动它，这里需要补充说明下，这里只是以NioEndPoint为示列，其实Tomcat 主要提供了三种实现，分别是AprEndPoint,NioEndPoint,Nio2EndPoint,这里表示了tomcat支持的I/O模型：
上述代码主要是开启两个线程，一个是Poller,一个是开启Acceptor，既然是线程，核心的代码肯定是run方法，我们来查看源码，代码如下：
//4.类：Acceptor<U> implements Runnable
public void run() {
//省略了部分代码
U socket = null;
socket = endpoint.serverSocketAccept();
// Configure the socket
if (endpoint.isRunning() && !endpoint.isPaused()) {
// setSocketOptions() will hand the socket off to
// an appropriate processor if successful
//核心逻辑
if (!endpoint.setSocketOptions(socket)) {
endpoint.closeSocket(socket);
}
} else {
endpoint.destroySocket(socket);
}
state = AcceptorState.ENDED;
}
//5.类：NioEndpoint
protected boolean setSocketOptions(SocketChannel socket) {
// Process the connection
//省略部分代码
try {
// Disable blocking, polling will be used
socket.configureBlocking(false);
Socket sock = socket.socket();
socketProperties.setProperties(sock);
NioSocketWrapper socketWrapper = new NioSocketWrapper(channel, this);
channel.setSocketWrapper(socketWrapper);
socketWrapper.setReadTimeout(getConnectionTimeout());
socketWrapper.setWriteTimeout(getConnectionTimeout());
socketWrapper.setKeepAliveLeft(NioEndpoint.this.getMaxKeepAliveRequests());
socketWrapper.setSecure(isSSLEnabled());
//核心逻辑
poller.register(channel, socketWrapper);
return true;
}
这里可以发现Acceptor主要就是接受socket,然后把它注册到poller中，我们继续看看是如何注册的。
/**6.类NioEndpoint
* Registers a newly created socket with the poller.
*
* @param socket The newly created socket
* @param socketWrapper The socket wrapper
*/
public void register(final NioChannel socket, final NioSocketWrapper socketWrapper) {
socketWrapper.interestOps(SelectionKey.OP_READ);//this is what OP_REGISTER turns into.
PollerEvent r = null;
if (eventCache != null) {
r = eventCache.pop();
}
if (r == null) {
r = new PollerEvent(socket, OP_REGISTER);
} else {
r.reset(socket, OP_REGISTER);
}
addEvent(r);
}
/** 7.类：PollerEvent implements Runnable
public void run() {
//省略部分代码
socket.getIOChannel().register(socket.getSocketWrapper().getPoller().getSelector(), SelectionKey.OP_READ, socket.getSocketWrapper());
}
这里发现最终就是采用NIO模型把其注册到通道中。(这里涉及NIO网络编程知识，不了解的同学可以传送这里)。那么注册完毕后，我们看看Poller做了什么事情。
*/
/**8.类：NioEndPoint内部类 Poller implements Runnable
**/
@Override
public void run() {
// Loop until destroy() is called
while (true) {
//省略部分代码
Iterator<SelectionKey> iterator =
keyCount > 0 ? selector.selectedKeys().iterator() : null;
// Walk through the collection of ready keys and dispatch
// any active event.
while (iterator != null && iterator.hasNext()) {
SelectionKey sk = iterator.next();
NioSocketWrapper socketWrapper = (NioSocketWrapper) sk.attachment();
// Attachment may be null if another thread has called
// cancelledKey()
if (socketWrapper == null) {
iterator.remove();
} else {
iterator.remove();
//sock处理
processKey(sk, socketWrapper);
}
}
//省略部分代码
}
这个就是通过selector把之前注册的事件取出来，从而完成了调用。
//9.类： NioEndPoint内部类 Poller implements Runnable
protected void processKey(SelectionKey sk, NioSocketWrapper socketWrapper) {
//省略大部分代码
processSocket(socketWrapper, SocketEvent.OPEN_WRITE, true)
}
//10.类：AbstractEndPoint
public boolean processSocket(SocketWrapperBase<S> socketWrapper,
SocketEvent event, boolean dispatch) {
//省略部分代码
Executor executor = getExecutor();
if (dispatch && executor != null) {
executor.execute(sc);
} else {
sc.run();
}
return true;
}
//11.类：SocketProcessorBase implements Runnable
public final void run() {
synchronized (socketWrapper) {
// It is possible that processing may be triggered for read and
// write at the same time. The sync above makes sure that processing
// does not occur in parallel. The test below ensures that if the
// first event to be processed results in the socket being closed,
// the subsequent events are not processed.
if (socketWrapper.isClosed()) {
return;
}
doRun();
}
}
//类：12.NioEndPoint extends AbstractJsseEndpoint<NioChannel,SocketChannel>
protected void doRun() {
//省略部分代码
if (handshake == 0) {
SocketState state = SocketState.OPEN;
// Process the request from this socket
if (event == null) {
state = getHandler().process(socketWrapper, SocketEvent.OPEN_READ);
} else {
state = getHandler().process(socketWrapper, event);
}
if (state == SocketState.CLOSED) {
poller.cancelledKey(key, socketWrapper);
}
}
}
Poller调用的run方法或者用Executor线程池去执行run(),最终调用都是各个子EndPoint中的doRun()方法，最终会取一个Handler去处理socketWrapper。继续看源码：
//类：13.AbstractProtocol内部类ConnectionHandler implements AbstractEndpoint.Handler<S>
public SocketState process(SocketWrapperBase<S> wrapper, SocketEvent status) {
//省略部分代码
state = processor.process(wrapper, status);
return SocketState.CLOSED;
}
//类：14.AbstractProcessorLight implements Processor
public SocketState process(SocketWrapperBase<?> socketWrapper, SocketEvent status)
throws IOException {
//省略部分代码
state = service(socketWrapper);
return state;
}
这部分源码表明最终调用的process是通过一个Processor接口的实现类来完成的，这里最终也是会调用到各个子类中，那么这里的处理器其实就是处理应用协议，我们可以查看AbstractProcessorLight的实现类，分别有AjpProcessor、Http11Processor、StreamProcessor，分别代表tomcat支持三种应用层协议，分别是：
这里我们以常用的HTTP1.1为例，继续看源码：
//类：15. Http11Processor extends AbstractProcessor
public SocketState service(SocketWrapperBase<?> socketWrapper)
throws IOException {
//省略大部分代码
getAdapter().service(request, response);
//省略大部分代码
}
//类：16 CoyoteAdapter implements Adapter
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);
postParseSuccess = postParseRequest(req, request, res, response);
if (postParseSuccess) {
//check valves if we support async
request.setAsyncSupported(
connector.getService().getContainer().getPipeline().isAsyncSupported());
// Calling the container
connector.getService().getContainer().getPipeline().getFirst().invoke(
request, response);
}
}
这里我们发现协议处理器最终会调用适配器(CoyoteAdapter),而适配器最终的工作是转换Request和Response对象为HttpServletRequest和HttpServletResponse，从而可以去调用容器，到这里整个连接器的流程和作用我们就已经分析完了。
小结
那么我们来回忆下整个流程，我画了一张时序图来说明：
这张图包含了两个流程，一个是组件的初始化，一个是调用的流程。连接器(Connector)主要初始化了两个组件，ProtcoHandler和EndPoint,但是我们从代码结构发现，他们两个是父子关系，也就是说ProtcoHandler包含了EndPoint。后面的流程就是各个子组件的调用链关系，总结来说就是Acceptor负责接收请求，然后注册到Poller，Poller负责处理请求，然后调用processor处理器来处理，最后把请求转成符合Servlet规范的request和response去调用容器(Container)。
我们流程梳理清楚了，接下来我们来结构化的梳理下：
回到连接器（Connector）是源码，我们发现，上述说的模块只有ProtocolHandler和Adapter两个属于连接器中，也就是说，连接器只包含了这两大子模块，那么后续的EndPoint、Acceptor、Poller、Processor都是ProtocolHandler的子模块。 而Acceptor和Poller两个模块的核心功能都是在EndPoint 中完成的，所以是其子模块，而Processor比较独立，所以它和EndPoint是一个级别的子模块。
我们用图来说明下上述的关系：
根据上图我们可以知道，连接器主要负责处理连接请求，然后通过适配器调用容器。那么具体流程细化可以如下：
Acceptor监听网络请求，获取请求。Poller获取到监听的请求提交线程池进行处理。Processor根据具体的应用协议（HTTP/AJP）来生成Tomcat Request对象。Adapter把Request对象转换成Servlet标准的Request对象，调用容器。
总结
我们从连接器的源码，一步一步解析，分析了连接器主要包含了两大模块，ProtocolHandler和Adapter。ProtocolHandler主要包含了Endpoint模块和Processor模块。Endpoint模块主要的作用是连接的处理，它委托了Acceptor子模块进行连接的监听和注册,委托子模块Poller进行连接的处理；而Processor模块主要是应用协议的处理，最后提交给Adapter进行对象的转换，以便可以调用容器(Container)。另外我们也在分析源码的过程中补充了一些额外知识点：
- 当前Tomcat版本支持的IO模型为：APR模型、NIO模型、NIO.2模型
- Tomcat支持的协议是AJP和HTTP,其中HTTP又分为HTTP1.1和HTTP2.0