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Tomcat源码解析之Web请求与处理

︶ㄣ米米素材网 メ
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这篇文章主要介绍了Tomcat源码解析之Web请求与处理,文中有非常详细的代码示例,对正在学习java的小伙伴们有很好的帮助,需要的朋友可以参考下

前言

tomcat最全uml类图

Tomcat源码解析之Web请求与处理

tomcat请求处理过程：

Tomcat源码解析之Web请求与处理

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。

Tomcat源码解析之Web请求与处理

一、endpoint

Tomcat源码解析之Web请求与处理

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。

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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。

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// 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。

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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。

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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。

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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。

Tomcat源码解析之Web请求与处理

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。

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@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

Tomcat源码解析之Web请求与处理

（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);

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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);

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@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。

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@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。

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@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。

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@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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原文链接：https://blog.csdn.net/qq_34037358/article/details/115579034