servlet & tomcat
在spring-mvc demo步调运行到DispatcherServlet的mvc处理 一文中，我们实践了欣赏器输入一个请求，然后到SpringMvc的DispatcherServlet处理的整个流程. 设计上这些都是tomcat servlet的处理https://i-blog.csdnimg.cn/direct/1710b30f7f9c4f8c9653a876cb2d9577.png
那么究竟这是怎么到DispatcherServlet处理的，本文将给出。
Tomcat架构
显然需要先了解tomcat， 可以下载tomcat源码分析。 其处理流程基本如下：
https://i-blog.csdnimg.cn/direct/bbdc4b242d1e4f46ae16e0453e193348.png
Tomcat包罗几个容器：Engine, Host, Context，Wrapper，Servlet，末了是Servlet实例实行service方法处理请求。
而Servlet 生命周期可被定义为从创建直到毁灭的整个过程。以下是 Servlet 遵照的过程：
[*]Servlet 通过调用init()方法举行初始化。
[*]Servlet 调用service()方法来处理客户端的请求。
[*]Servlet 通过调用destroy()方法终止（结束）。
[*]末了，Servlet 是由 JVM 的垃圾回收器举行垃圾回收的。
service()方法是实行现实使命的主要方法。Servlet 容器（即 Web 服务器）调用 service() 方法来处理来自客户端（欣赏器）的请求，并把格式化的响应写回给客户端。每次服务器接收到一个 Servlet 请求时，服务器会产生一个新的线程并调用服务。service() 方法检查 HTTP 请求范例（GET、POST、PUT、DELETE 等），并在适当的时候调用 doGet、doPost、doPut，doDelete等方法。
Connector
connector是什么？
The HTTP Connector element represents a Connector component that supports the HTTP/1.1 protocol. It enables Catalina to function as a stand-alone web server, in addition to its ability to execute servlets and JSP pages. A particular instance of this component listens for connections on a specific TCP port number on the server.One or more such Connectors can be configured as part of a single Service, each forwarding to the associated Engine to perform request processing and create the response.
（https://tomcat.apache.org/tomcat-8.0-doc/config/http.html）
HTTP Connector 能支持 HTTP/1.1 协议。它使 Catalina 可以或许作为独立的 Web 服务器运行，别的还可以或许实行 servlet 和 JSP 页面。此组件的特定实例会侦听服务器上特定 TCP 端口号上的连接。可以将一个或多个如许的 Connector 设置为单个服务的一部分，每个 Connector 都会转发到关联的 Engine 以实行请求处理并创建响应。
public Connector(String protocol) {
setProtocol(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;
}
if (Globals.STRICT_SERVLET_COMPLIANCE) {
uriCharset = StandardCharsets.ISO_8859_1;
} else {
uriCharset = StandardCharsets.UTF_8;
}
// Default for Connector depends on this (deprecated) system property
if (Boolean.parseBoolean(System.getProperty("org.apache.tomcat.util.buf.UDecoder.ALLOW_ENCODED_SLASH", "false"))) {
encodedSolidusHandling = EncodedSolidusHandling.DECODE;
}
}
第一句 setProtocol就根据设置了socket编程协议范例
/**
* Set the Coyote protocol which will be used by the connector.
*
* @param protocol The Coyote protocol name
*
* @deprecated Will be removed in Tomcat 9. Protocol must be configured via
* the constructor
*/
@Deprecated
public void setProtocol(String protocol) {
boolean aprConnector = AprLifecycleListener.isAprAvailable() &&
AprLifecycleListener.getUseAprConnector();
if ("HTTP/1.1".equals(protocol) || protocol == null) {
if (aprConnector) {
setProtocolHandlerClassName("org.apache.coyote.http11.Http11AprProtocol");
} else {
setProtocolHandlerClassName("org.apache.coyote.http11.Http11NioProtocol");
}
} else if ("AJP/1.3".equals(protocol)) {
if (aprConnector) {
setProtocolHandlerClassName("org.apache.coyote.ajp.AjpAprProtocol");
} else {
setProtocolHandlerClassName("org.apache.coyote.ajp.AjpNioProtocol");
}
} else {
setProtocolHandlerClassName(protocol);
}
}
Http11NioProtocol -> NioEndpoint
接收tcp/ip请求的线程，Acceptor
protected final void startAcceptorThreads() {
int count = getAcceptorThreadCount();
acceptors = new Acceptor;
for (int i = 0; i < count; i++) {
acceptors = createAcceptor();
String threadName = getName() + "-Acceptor-" + i;
acceptors.setThreadName(threadName);
Thread t = new Thread(acceptors, threadName);
t.setPriority(getAcceptorThreadPriority());
t.setDaemon(getDaemon());
t.start();
}
}
直接：java.nio.channels.ServerSocketChannel#accept (所以时候都要知道socket编程和tcp协议，IO底子可复习：https://doctording.blog.csdn.net/article/details/145839941)
/**
* The background thread that listens for incoming TCP/IP connections and
* hands them off to an appropriate processor.
*/
protected class Acceptor extends AbstractEndpoint.Acceptor {
@Override
public void run() {
int errorDelay = 0;
// Loop until we receive a shutdown command
while (running) {
// Loop if endpoint is paused
while (paused && running) {
state = AcceptorState.PAUSED;
try {
Thread.sleep(50);
} catch (InterruptedException e) {
// Ignore
}
}
if (!running) {
break;
}
state = AcceptorState.RUNNING;
try {
//if we have reached max connections, wait
countUpOrAwaitConnection();
SocketChannel socket = null;
try {
// Accept the next incoming connection from the server
// socket
socket = serverSock.accept();
} catch (IOException ioe) {
// We didn't get a socket
countDownConnection();
if (running) {
// Introduce delay if necessary
errorDelay = handleExceptionWithDelay(errorDelay);
// re-throw
throw ioe;
} else {
break;
}
}
// Successful accept, reset the error delay
errorDelay = 0;
// Configure the socket
if (running && !paused) {
// setSocketOptions() will hand the socket off to
// an appropriate processor if successful
if (!setSocketOptions(socket)) {
closeSocket(socket);
}
} else {
closeSocket(socket);
}
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
log.error(sm.getString("endpoint.accept.fail"), t);
}
}
state = AcceptorState.ENDED;
}
处理socket连接数据的线程，Poller
Acceptor的到的连接socket，举行如下处理
/**
* Process the specified connection.
* @param socket The socket channel
* @return <code>true</code> if the socket was correctly configured
*and processing may continue, <code>false</code> if the socket needs to be
*close immediately
*/
protected boolean setSocketOptions(SocketChannel socket) {
// Process the connection
try {
//disable blocking, APR style, we are gonna be polling it
socket.configureBlocking(false);
Socket sock = socket.socket();
socketProperties.setProperties(sock);
NioChannel channel = nioChannels.pop();
if (channel == null) {
SocketBufferHandler bufhandler = new SocketBufferHandler(
socketProperties.getAppReadBufSize(),
socketProperties.getAppWriteBufSize(),
socketProperties.getDirectBuffer());
if (isSSLEnabled()) {
channel = new SecureNioChannel(socket, bufhandler, selectorPool, this);
} else {
channel = new NioChannel(socket, bufhandler);
}
} else {
channel.setIOChannel(socket);
channel.reset();
}
getPoller0().register(channel);
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
try {
log.error("",t);
} catch (Throwable tt) {
ExceptionUtils.handleThrowable(tt);
}
// Tell to close the socket
return false;
}
return true;
}
Pollor类定义如下:
Pollor负责轮询网络连接上的数据。在 NIO 或 NIO2 模型中，Poller 线程会检查注册在其上的 Channel（例如，SocketChannel）是否有数据可读或可写。
此中使用了java nio的Selector，即允许一个单一的线程来操作多个 Channel.
/**
* Poller class.
*/
public class Poller implements Runnable {
private Selector selector;
private final SynchronizedQueue<PollerEvent> events =
new SynchronizedQueue<>();
private volatile boolean close = false;
private long nextExpiration = 0;//optimize expiration handling
private AtomicLong wakeupCounter = new AtomicLong(0);
private volatile int keyCount = 0;
public Poller() throws IOException {
this.selector = Selector.open();
}
socket详细的读写处理，Processor（Executor线程池）
Poller判断连接是否有读写，交给Processor详细处理
protected void processKey(SelectionKey sk, NioSocketWrapper attachment) {
try {
if ( close ) {
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
if (sk.isReadable()) {
if (!processSocket(attachment, SocketEvent.OPEN_READ, true)) {
closeSocket = true;
}
}
if (!closeSocket && sk.isWritable()) {
if (!processSocket(attachment, SocketEvent.OPEN_WRITE, true)) {
closeSocket = true;
}
}
if (closeSocket) {
cancelledKey(sk);
}
}
}
} else {
//invalid key
cancelledKey(sk);
}
} catch ( CancelledKeyException ckx ) {
cancelledKey(sk);
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
log.error("",t);
}
}
背后是扩展的Executor线程池处理
/**
* This class is the equivalent of the Worker, but will simply use in an
* external Executor thread pool.
*/
protected class SocketProcessor extends SocketProcessorBase<NioChannel> {
public SocketProcessor(SocketWrapperBase<NioChannel> socketWrapper, SocketEvent event) {
super(socketWrapper, event);
}
@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()) {
// No TLS handshaking required. Let the handler
// process this socket / event combination.
handshake = 0;
} else if (event == SocketEvent.STOP || event == SocketEvent.DISCONNECT ||
event == SocketEvent.ERROR) {
// Unable to complete the TLS handshake. Treat it as
// if the handshake failed.
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.
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) {
state = getHandler().process(socketWrapper, SocketEvent.OPEN_READ);
} else {
state = getHandler().process(socketWrapper, event);
}
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){
socketWrapper.registerReadInterest();
} else if (handshake == SelectionKey.OP_WRITE){
socketWrapper.registerWriteInterest();
}
} catch (CancelledKeyException cx) {
socket.getPoller().cancelledKey(key);
} catch (VirtualMachineError vme) {
ExceptionUtils.handleThrowable(vme);
} catch (Throwable t) {
log.error("", t);
socket.getPoller().cancelledKey(key);
} finally {
socketWrapper = null;
event = null;
//return to cache
if (running && !paused) {
processorCache.push(this);
}
}
}
}
详细在抽象类AbstractEndpoint中org.apache.tomcat.util.net.AbstractEndpoint#processSocket
/**
* Process the given SocketWrapper with the given status. Used to trigger
* processing as if the Poller (for those endpoints that have one)
* selected the socket.
*
* @param socketWrapper The socket wrapper to process
* @param event The socket event to be processed
* @param dispatch Should the processing be performed on a new
* container thread
*
* @return if processing was triggered successfully
*/
public boolean processSocket(SocketWrapperBase<S> socketWrapper,
SocketEvent event, boolean dispatch) {
try {
if (socketWrapper == null) {
return false;
}
SocketProcessorBase<S> sc = processorCache.pop();
if (sc == null) {
sc = createSocketProcessor(socketWrapper, event);
} else {
sc.reset(socketWrapper, event);
}
Executor executor = getExecutor();
if (dispatch && executor != null) {
executor.execute(sc);
} else {
sc.run();
}
} catch (RejectedExecutionException ree) {
getLog().warn(sm.getString("endpoint.executor.fail", socketWrapper) , ree);
return false;
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
// This means we got an OOM or similar creating a thread, or that
// the pool and its queue are full
getLog().error(sm.getString("endpoint.process.fail"), t);
return false;
}
return true;
}
（大概差异版本不一样，如上是在tomcat-8.5.57源码中）
org.apache.coyote.http11.Http11Processor#service
详细的processor处理，则依据设置和socket连接，如Http11Processor处理如下：
@Override
public SocketState service(SocketWrapperBase<?> socketWrapper)
throws IOException {
RequestInfo rp = request.getRequestProcessor();
rp.setStage(org.apache.coyote.Constants.STAGE_PARSE);
// Setting up the I/O
setSocketWrapper(socketWrapper);
// Flags
keepAlive = true;
openSocket = false;
readComplete = true;
boolean keptAlive = false;
SendfileState sendfileState = SendfileState.DONE;
while (!getErrorState().isError() && keepAlive && !isAsync() && upgradeToken == null &&
sendfileState == SendfileState.DONE && !endpoint.isPaused()) {
// Parsing the request header
try {
if (!inputBuffer.parseRequestLine(keptAlive)) {
if (inputBuffer.getParsingRequestLinePhase() == -1) {
return SocketState.UPGRADING;
} else if (handleIncompleteRequestLineRead()) {
break;
}
}
// Process the Protocol component of the request line
// Need to know if this is an HTTP 0.9 request before trying to
// parse headers.
prepareRequestProtocol();
if (endpoint.isPaused()) {
// 503 - Service unavailable
response.setStatus(503);
setErrorState(ErrorState.CLOSE_CLEAN, null);
} else {
keptAlive = true;
// Set this every time in case limit has been changed via JMX
request.getMimeHeaders().setLimit(endpoint.getMaxHeaderCount());
// Don't parse headers for HTTP/0.9
if (!http09 && !inputBuffer.parseHeaders()) {
// We've read part of the request, don't recycle it
// instead associate it with the socket
openSocket = true;
readComplete = false;
break;
}
if (!disableUploadTimeout) {
socketWrapper.setReadTimeout(connectionUploadTimeout);
}
}
关键处理在getAdapter().service(request, response);
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