Tomcat源码解析之Web请求与处理
109人参与2021-05-07
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_unavailable,
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_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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