结合 tomcat 处理流程分析 Filter 的执行

作者: 晴天哥_王志 | 来源:发表于2022-08-10 23:29 被阅读0次

缘起

大约3-4年前看过 Tomcat 的源码，那时候主要聚焦在 Tomcat 加载 war 包的过程；一个星期前的周末在研究拦截器 Filter 的过程中发现可以整合Tomcat的执行流程来一并分析，所以就有了这篇文章。
文章的输出很大程度取决于日常的积累，时机到了就会有相应的输出，基本上没有其他更快的路径了。

Tomcat 线程模型

Acceptor线程：全局唯一，负责接受请求，并将请求放入Poller线程的事件队列。Accetpr线程在分发事件的时候，采用的Round Robin的方式来分发的
Poller线程：官方的建议是每个处理器配一个，但不要超过两个，由于现在几乎都是多核处理器，所以一般来说都是两个。每个Poller线程各自维护一个事件队列（无上限），它的职责是从事件队列里面拿出socket，往自己的selector上注册，然后等待selector选择读写事件，并交给SocketProcessor线程去实际处理请求。
SocketProcessor线程池：tomcat的默认配置是250(参见server.xml里面的maxThreads)，它是实际的工作线程，用于处理请求。

Tomcat 执行流程

tomcat 执行流程

Tomcat 监听过程

public class NioEndpoint extends AbstractJsseEndpoint<NioChannel> {

    private NioSelectorPool selectorPool = new NioSelectorPool();
    private ServerSocketChannel serverSock = null;
    private Executor executor = null;

    public final void start() throws Exception {
        if (bindState == BindState.UNBOUND) {
            bind();
            bindState = BindState.BOUND_ON_START;
        }
        startInternal();
    }

    @Override
    public void bind() throws Exception {
        // 创建 serverSock 执行绑定
        serverSock = ServerSocketChannel.open();

        socketProperties.setProperties(serverSock.socket());
        InetSocketAddress addr = (getAddress()!=null?new InetSocketAddress(getAddress(),getPort()):new InetSocketAddress(getPort()));
        serverSock.socket().bind(addr,getAcceptCount());
        serverSock.configureBlocking(true); 

        if (acceptorThreadCount == 0) {
            acceptorThreadCount = 1;
        }
        if (pollerThreadCount <= 0) {
            pollerThreadCount = 1;
        }
        setStopLatch(new CountDownLatch(pollerThreadCount));
        initialiseSsl();
        selectorPool.open();
    }


    @Override
    public void startInternal() throws Exception {
        if (!running) {
            running = true;
            paused = false;

            processorCache = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                    socketProperties.getProcessorCache());
            eventCache = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                            socketProperties.getEventCache());
            nioChannels = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
                    socketProperties.getBufferPool());

            // 创建 Poller 执行任务的线程
            if ( getExecutor() == null ) {
                createExecutor();
            }

            initializeConnectionLatch();

            // 开启 Poller 相关的线程
            pollers = new Poller[getPollerThreadCount()];
            for (int i=0; i<pollers.length; i++) {
                pollers[i] = new Poller();
                Thread pollerThread = new Thread(pollers[i], getName() + "-ClientPoller-"+i);
                pollerThread.setPriority(threadPriority);
                pollerThread.setDaemon(true);
                pollerThread.start();
            }

            // 启动Acceptor线程
            startAcceptorThreads();
        }
    }

    protected final void startAcceptorThreads() {
        int count = getAcceptorThreadCount();
        acceptors = new Acceptor[count];

        for (int i = 0; i < count; i++) {
            acceptors[i] = createAcceptor();
            String threadName = getName() + "-Acceptor-" + i;
            acceptors[i].setThreadName(threadName);
            Thread t = new Thread(acceptors[i], threadName);
            t.setPriority(getAcceptorThreadPriority());
            t.setDaemon(getDaemon());
            t.start();
        }
    }


    public void createExecutor() {
        internalExecutor = true;
        TaskQueue taskqueue = new TaskQueue();
        TaskThreadFactory tf = new TaskThreadFactory(getName() + "-exec-", daemon, getThreadPriority());
        executor = new ThreadPoolExecutor(getMinSpareThreads(), getMaxThreads(), 60, TimeUnit.SECONDS,taskqueue, tf);
        taskqueue.setParent( (ThreadPoolExecutor) executor);
    }
}

Tomcat 监听过程负责创建监听 socket 并进行 bind 操作，参见bind()方法。
Tomcat 负责创建Poller对象并绑定对应的Poller线程。
Tomcat 负责创建Acceptor对象并绑定对应的Acceptor线程。
Tomcat 负责创建SocketProcessor执行的线程池对象 Executor。

Tomcat 连接处理过程

public class NioEndpoint extends AbstractJsseEndpoint<NioChannel> {

    private ServerSocketChannel serverSock = null;

    protected class Acceptor extends AbstractEndpoint.Acceptor {
        @Override
        public void run() {
            while (running) {
                // 省略相关代码
                state = AcceptorState.RUNNING;
                try {
                    SocketChannel socket = null;
                    try {
                        // 获取新的链接
                        socket = serverSock.accept();
                    } catch (IOException ioe) {
                    }

                    if (running && !paused) {
                        // 通过setSocketOptions设置新连接的socket
                        if (!setSocketOptions(socket)) {
                            closeSocket(socket);
                        }
                    } 
                } catch (Throwable t) {
                }
            }
            state = AcceptorState.ENDED;
        }
    }

    protected boolean setSocketOptions(SocketChannel socket) {
        try {
            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();
            }
            // 注册对应的 Poller 当中
            getPoller0().register(channel);
        } catch (Throwable t) {
            return false;
        }
        return true;
    }

    public Poller getPoller0() {
        int idx = Math.abs(pollerRotater.incrementAndGet()) % pollers.length;
        return pollers[idx];
    }
}

Acceptor线程接受请求，从nioChannels里拿出NioChannel对象。从Poller 队列中轮询拿到一个 Poller 后关联 NioChannel。
setSocketOptions的getPoller0().register(channel)负责注册 accept 的NioChannel到Poller中。

Tomcat Socket 注册过程

public class NioEndpoint extends AbstractJsseEndpoint<NioChannel> {

    public class Poller implements Runnable {

        private Selector selector;
        private final SynchronizedQueue<PollerEvent> events =
                new SynchronizedQueue<>();
        private volatile boolean close = false;
        private long nextExpiration = 0;
        private AtomicLong wakeupCounter = new AtomicLong(0);
        private volatile int keyCount = 0;

        public Poller() throws IOException {
            this.selector = Selector.open();
        }

        public void register(final NioChannel socket) {
            socket.setPoller(this);
            // 包装 socket 成 NioSocketWrapper对象进行处理
            NioSocketWrapper ka = new NioSocketWrapper(socket, NioEndpoint.this);
            socket.setSocketWrapper(ka);
            ka.setPoller(this);
            ka.setReadTimeout(getSocketProperties().getSoTimeout());
            ka.setWriteTimeout(getSocketProperties().getSoTimeout());
            ka.setKeepAliveLeft(NioEndpoint.this.getMaxKeepAliveRequests());
            ka.setSecure(isSSLEnabled());
            ka.setReadTimeout(getConnectionTimeout());
            ka.setWriteTimeout(getConnectionTimeout());
            PollerEvent r = eventCache.pop();

            // 注意对应的事件
            ka.interestOps(SelectionKey.OP_READ);//this is what OP_REGISTER turns into.
            if ( r==null) r = new PollerEvent(socket,ka,OP_REGISTER);
            else r.reset(socket,ka,OP_REGISTER);
            addEvent(r);
        }

        private void addEvent(PollerEvent event) {
            events.offer(event);
            if ( wakeupCounter.incrementAndGet() == 0 ) selector.wakeup();
        }

        public boolean events() {
            boolean result = false;
            PollerEvent pe = null;
            while ( (pe = events.poll()) != null ) {
                result = true;
                try {
                    pe.run();
                    pe.reset();
                    if (running && !paused) {
                        eventCache.push(pe);
                    }
                } catch ( Throwable x ) {
                }
            }

            return result;
        }

        public void run() {
            while (true) {
                boolean hasEvents = false;
                try {
                    if (!close) {
                        hasEvents = events();
                    }
                } catch (Throwable x) {
                }
                // 省略代码
            }
        }
    }


    public static class PollerEvent implements Runnable {

        private NioChannel socket;
        private int interestOps;
        private NioSocketWrapper socketWrapper;

        public PollerEvent(NioChannel ch, NioSocketWrapper w, int intOps) {
            reset(ch, w, intOps);
        }

        @Override
        public void run() {
            if (interestOps == OP_REGISTER) {
                try {
                    socket.getIOChannel().register(
                            socket.getPoller().getSelector(), SelectionKey.OP_READ, socketWrapper);
                } catch (Exception x) {
                }
            } 
        }
    }
}

Poller实现NioChannel的register过程通过PollerEvent的创建和提交来实现。
Poller的 run 方法中会调用PollerEvent的 run 方法，进而实现NioChannel的注册。

Tomcat Socket 任务处理过程

public class NioEndpoint extends AbstractJsseEndpoint<NioChannel> {
    public class Poller implements Runnable {
        @Override
        public void run() {
            while (true) {
                // 省略代码
                Iterator<SelectionKey> iterator =
                    keyCount > 0 ? selector.selectedKeys().iterator() : null;

                while (iterator != null && iterator.hasNext()) {
                    SelectionKey sk = iterator.next();
                    NioSocketWrapper attachment = (NioSocketWrapper)sk.attachment();

                    if (attachment == null) {
                        iterator.remove();
                    } else {
                        iterator.remove();
                        // 处理连接请求
                        processKey(sk, attachment);
                    }
                }
                timeout(keyCount,hasEvents);
            }
        }

        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;
                            if (sk.isReadable()) {
                                // 处理可读事件
                                if (!processSocket(attachment, SocketEvent.OPEN_READ, true)) {
                                    closeSocket = true;
                                }
                            }
                        }
                    }
                } 
            }  catch (Throwable t) {
            }
        }
    }

    public boolean processSocket(SocketWrapperBase<S> socketWrapper,
            SocketEvent event, boolean dispatch) {
        try {
            if (socketWrapper == null) {
                return false;
            }
            // SocketProcessor对象
            SocketProcessorBase<S> sc = processorCache.pop();
            if (sc == null) {
                sc = createSocketProcessor(socketWrapper, event);
            } else {
                sc.reset(socketWrapper, event);
            }
            Executor executor = getExecutor();
            if (dispatch && executor != null) {
                // 执行对应的连接请求
                executor.execute(sc);
            } else {
                sc.run();
            }
        } catch (RejectedExecutionException ree) {
            return false;
        } catch (Throwable t) {
            return false;
        }
        return true;
    }
}

Poller注册NioChannel后通过 select 方法返回待处理的NioSocketWrapper对象，进而包装成SocketProcessor后提交Executor 进行处理。

Tomcat 请求处理过程

public class NioEndpoint extends AbstractJsseEndpoint<NioChannel> {

   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;

                // 省略代码

                if (handshake == 0) {
                    SocketState state = SocketState.OPEN;
                    // 通过ConnectionHandler 处理请求
                    if (event == null) {
                        state = getHandler().process(socketWrapper, SocketEvent.OPEN_READ);
                    } else {
                        state = getHandler().process(socketWrapper, event);
                    }
                    if (state == SocketState.CLOSED) {
                        close(socket, key);
                    }
                } 
            } catch (Throwable t) {
            } finally {
            }
        }
    }
}

SocketProcessor作为封装任务内部仅执行ConnectionHandler的 proces 方法。

ConnectionHandler处理过程

public abstract class AbstractProtocol<S> implements ProtocolHandler,
        MBeanRegistration {

    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);
        private final Map<S,Processor> connections = new ConcurrentHashMap<>();
        private final RecycledProcessors recycledProcessors = new RecycledProcessors(this);

        @Override
        public SocketState process(SocketWrapperBase<S> wrapper, SocketEvent status) {
                // 省略相关代码
                if (processor == null) {
                    processor = recycledProcessors.pop();
                }
                if (processor == null) {
                    processor = getProtocol().createProcessor();
                    register(processor);
                }

                do {
                    // 执行Http11Processor的 process 方法
                    state = processor.process(wrapper, status);
                } while ( state == SocketState.UPGRADING);

                return state;
            } catch (Throwable e) {
            } 
        }
    }
}

public abstract class AbstractHttp11Protocol<S> extends AbstractProtocol<S> {
    @Override
    protected Processor createProcessor() {
        // 创建Http11Processor对象
        Http11Processor processor = new Http11Processor(getMaxHttpHeaderSize(),
                getAllowHostHeaderMismatch(), getRejectIllegalHeaderName(), getEndpoint(),
                getMaxTrailerSize(), allowedTrailerHeaders, getMaxExtensionSize(),
                getMaxSwallowSize(), httpUpgradeProtocols, getSendReasonPhrase());
        // 省略相关代码
        return processor;
    }
}

public class Http11Processor extends AbstractProcessor {

    public Http11Processor(int maxHttpHeaderSize, boolean allowHostHeaderMismatch,
            boolean rejectIllegalHeaderName, AbstractEndpoint<?> endpoint, int maxTrailerSize,
            Set<String> allowedTrailerHeaders, int maxExtensionSize, int maxSwallowSize,
            Map<String,UpgradeProtocol> httpUpgradeProtocols, boolean sendReasonPhrase) {

        super(endpoint);
        // 省略相关代码
    }
}

public abstract class AbstractProcessor extends AbstractProcessorLight implements ActionHook {
    protected Adapter adapter;
    protected final AsyncStateMachine asyncStateMachine;
    private volatile long asyncTimeout = -1;
    protected final AbstractEndpoint<?> endpoint;
    protected final Request request;
    protected final Response response;
    protected volatile SocketWrapperBase<?> socketWrapper = null;
    protected volatile SSLSupport sslSupport;
    private ErrorState errorState = ErrorState.NONE;

    public AbstractProcessor(AbstractEndpoint<?> endpoint) {
        this(endpoint, new Request(), new Response());
    }

    protected AbstractProcessor(AbstractEndpoint<?> endpoint, Request coyoteRequest,
            Response coyoteResponse) {
        this.endpoint = endpoint;
        asyncStateMachine = new AsyncStateMachine(this);
        request = coyoteRequest;
        response = coyoteResponse;
        response.setHook(this);
        request.setResponse(response);
        request.setHook(this);
    }
}

ConnectionHandler通过Http11NioProtocol的createProcessor方法创建 Processor对象。通过recycledProcessors实现processor的重用性。
Http11Processor作为processor 对象，内部包含Request和Response对象。
Http11Processor的process方法负责处理请求逻辑。
Http11Processor的重用意味着每次请来请求都要重置内部Request和Response对象。

Http11Processor 处理过程

public abstract class AbstractProcessorLight implements Processor {

    private Set<DispatchType> dispatches = new CopyOnWriteArraySet<>();
    protected Adapter adapter;
    // Http11Processor内部包含Request 和 Response对象
    protected final Request request;
    protected final Response response;

    @Override
    public SocketState process(SocketWrapperBase<?> socketWrapper, SocketEvent status)
            throws IOException {

        SocketState state = SocketState.CLOSED;
        Iterator<DispatchType> dispatches = null;
        do {
            if (dispatches != null) {
            } else if (status == SocketEvent.OPEN_READ){
                // 执行对应的逻辑
                state = service(socketWrapper);
            } 
            // 省略相关代码
        } while (state == SocketState.ASYNC_END ||
                dispatches != null && state != SocketState.CLOSED);

        return state;
    }
}

public abstract class AbstractProcessor 
       extends AbstractProcessorLight implements ActionHook {

    protected Adapter adapter;
    private volatile long asyncTimeout = -1;
    protected final AbstractEndpoint<?> endpoint;
    protected final Request request;
    protected final Response response;
    protected volatile SocketWrapperBase<?> socketWrapper = null;
}

public class Http11Processor extends AbstractProcessor {

    @Override
    public SocketState service(SocketWrapperBase<?> socketWrapper)
        throws IOException {
        // 省略相关代码
        while (!getErrorState().isError() && keepAlive && !isAsync() && upgradeToken == null &&
                sendfileState == SendfileState.DONE && !endpoint.isPaused()) {
            try {
                // 解析请求
                if (!inputBuffer.parseRequestLine(keptAlive)) {
                    if (inputBuffer.getParsingRequestLinePhase() == -1) {
                        return SocketState.UPGRADING;
                    } else if (handleIncompleteRequestLineRead()) {
                        break;
                    }
                }
            } catch (Throwable t) {
            }

            // 解析 Request 对象
            if (!getErrorState().isError()) {
                try {
                    prepareRequest();
                } catch (Throwable t) {
                }
            }

            if (!getErrorState().isError()) {
                try {
                    getAdapter().service(request, response);
                } catch (Throwable t) {
                }
            }

            sendfileState = processSendfile(socketWrapper);
        }
    }
}

Http11Processor对象能够被重用，每次处理请求都会重新初始化Request对象。
Http11Processor处理每次请求通过inputBuffer.parseRequestLine和prepareRequest来重新初始化Request对象。
Http11Processor的 service 内部调用CoyoteAdapter的service方法。

CoyoteAdapter 执行流程

org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
      // 5、StandardWrapperValve
      at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
      // 4、StandardContextValve
      at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
      at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478)
      // 3、StandardHostValve
      at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
      at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
      // 2、StandardEngineValve
      at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
      // 1、CoyoteAdapter
      at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
      at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803)
      at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
      at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
      at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
      at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
      - locked <0x19b6> (a org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
      at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
      at java.lang.Thread.run(Thread.java:748)

CoyoteAdapter的执行流程按照 Tomcat 内部对象的经典顺序进行执行，见调用栈注释。
整个执行过程最终调用的是StandardWrapperValve的 invoke 方法。

Tomcat Filter职责链

final class StandardWrapperValve
    extends ValveBase {

    public StandardWrapperValve() {
        super(true);
    }

    @Override
    public final void invoke(Request request, Response response)
        throws IOException, ServletException {

        Servlet servlet = null;

        try {
            if (!unavailable) {
                // wrapper是StandardEngine[Tomcat].StandardHost[localhost].TomcatEmbeddedContext[].StandardWrapper
                // 创建一个 servlet 对象
                servlet = wrapper.allocate();
            }
        } catch (Throwable e) {
        }

        // 创建过滤器职责链
        ApplicationFilterChain filterChain =
                ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);

        try {
            if ((servlet != null) && (filterChain != null)) {
                if (context.getSwallowOutput()) {
                    // 省略代码
                } else {
                    if (request.isAsyncDispatching()) {
                        request.getAsyncContextInternal().doInternalDispatch();
                    } else {
                        // 通过职责链开始执行
                        filterChain.doFilter
                            (request.getRequest(), response.getResponse());
                    }
                }
            }
        } catch (Throwable e) {
        }

        // 释放职责链，职责链的释放表示所有的filter 设置为 null
        if (filterChain != null) {
            filterChain.release();
        }

        // 回收 servlet 对象
        try {
            if (servlet != null) {
                wrapper.deallocate(servlet);
            }
        } catch (Throwable e) {
        }
    }

    public HttpServletResponse getResponse() {
        if (facade == null) {
            facade = new ResponseFacade(this);
        }
        if (applicationResponse == null) {
            applicationResponse = facade;
        }
        return applicationResponse;
    }

    public HttpServletRequest getRequest() {
        if (facade == null) {
            facade = new RequestFacade(this);
        }
        if (applicationRequest == null) {
            applicationRequest = facade;
        }
        return applicationRequest;
    }
}

StandardWrapperValve负责创建经典的 servlet 对象，通过wrapper.allocate创建，内部实现了 servlet 的单例模式。
StandardWrapperValve负责创建 FilterChain 对象，通过createFilterChain方法。
filterChain.doFilter方法中的request.getRequest()和response.getResponse()负责将 request 对象转换成RequestFacade对象，将 response 对象转换成ResponseFacade对象。

Tomcat FilterChain创建和释放

public final class ApplicationFilterChain implements FilterChain {

    private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];
    private int pos = 0;
    private int n = 0;
    public static final int INCREMENT = 10;
    private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];
    private Servlet servlet = null;
}

public final class ApplicationFilterFactory {
    public static ApplicationFilterChain createFilterChain(ServletRequest request,
            Wrapper wrapper, Servlet servlet) {

        ApplicationFilterChain filterChain = null;

        if (request instanceof Request) {
            Request req = (Request) request;
            if (Globals.IS_SECURITY_ENABLED) {
                filterChain = new ApplicationFilterChain();
            } else {
                filterChain = (ApplicationFilterChain) req.getFilterChain();
                if (filterChain == null) {
                    filterChain = new ApplicationFilterChain();
                    req.setFilterChain(filterChain);
                }
            }
        } else {
            filterChain = new ApplicationFilterChain();
        }

        // 设置职责链的filterChain内部的 sevlet 对象
        filterChain.setServlet(servlet);
        filterChain.setServletSupportsAsync(wrapper.isAsyncSupported());

        StandardContext context = (StandardContext) wrapper.getParent();
        FilterMap filterMaps[] = context.findFilterMaps();

        if ((filterMaps == null) || (filterMaps.length == 0))
            return (filterChain);

        DispatcherType dispatcher =
                (DispatcherType) request.getAttribute(Globals.DISPATCHER_TYPE_ATTR);

        String requestPath = null;
        Object attribute = request.getAttribute(Globals.DISPATCHER_REQUEST_PATH_ATTR);
        if (attribute != null){
            requestPath = attribute.toString();
        }

        String servletName = wrapper.getName();

        // Add the relevant path-mapped filters to this filter chain
        for (int i = 0; i < filterMaps.length; i++) {
            if (!matchDispatcher(filterMaps[i] ,dispatcher)) {
                continue;
            }
            if (!matchFiltersURL(filterMaps[i], requestPath))
                continue;
            ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
                context.findFilterConfig(filterMaps[i].getFilterName());
            if (filterConfig == null) {
                // FIXME - log configuration problem
                continue;
            }
            filterChain.addFilter(filterConfig);
        }

        // Add filters that match on servlet name second
        for (int i = 0; i < filterMaps.length; i++) {
            if (!matchDispatcher(filterMaps[i] ,dispatcher)) {
                continue;
            }
            if (!matchFiltersServlet(filterMaps[i], servletName))
                continue;
            ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
                context.findFilterConfig(filterMaps[i].getFilterName());
            if (filterConfig == null) {
                continue;
            }
            filterChain.addFilter(filterConfig);
        }

        return filterChain;
    }

    void addFilter(ApplicationFilterConfig filterConfig) {

        for(ApplicationFilterConfig filter:filters)
            if(filter==filterConfig)
                return;

        if (n == filters.length) {
            ApplicationFilterConfig[] newFilters =
                new ApplicationFilterConfig[n + INCREMENT];
            System.arraycopy(filters, 0, newFilters, 0, n);
            filters = newFilters;
        }
        filters[n++] = filterConfig;
    }


    void release() {
        for (int i = 0; i < n; i++) {
            filters[i] = null;
        }
        n = 0;
        pos = 0;
        servlet = null;
        servletSupportsAsync = false;
    }
}

FilterChain内部包含ApplicationFilterConfig数组保存Filter 对象。
FilterChain每次请求开始的时候进行创建，结束的时候负责回收（参考release方法）。

Tomcat FilterChain的执行

public final class ApplicationFilterChain implements FilterChain {

    private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];
    private int pos = 0;
    private int n = 0;
    public static final int INCREMENT = 10;
    private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];
    private Servlet servlet = null;

    @Override
    public void doFilter(ServletRequest request, ServletResponse response)
        throws IOException, ServletException {

        if( Globals.IS_SECURITY_ENABLED ) {
            // 省略相关代码
        } else {
            internalDoFilter(request,response);
        }

    private void internalDoFilter(ServletRequest request,
                                  ServletResponse response)
        throws IOException, ServletException {

        // 执行职责链
        if (pos < n) {
            ApplicationFilterConfig filterConfig = filters[pos++];
            try {
                Filter filter = filterConfig.getFilter();
                if( Globals.IS_SECURITY_ENABLED ) {
                   // 省略代码
                } else {
                    filter.doFilter(request, response, this);
                }
            } catch (Throwable e) {
            }
            return;
        }

        // 执行 servlet 本身的服务
        try {
            if ((request instanceof HttpServletRequest) &&
                    (response instanceof HttpServletResponse) &&
                    Globals.IS_SECURITY_ENABLED ) {
               // 省略相关代码
            } else {
                // 执行 serlvet 的服务，默认是DispatcherServlet对象
                servlet.service(request, response);
            }
        } catch (Throwable e) {
        } finally {
        }
    }
 }

职责链的执行有两种视角，一种是以上帝视角外部调用 for 循环执行，一种是每个 Filter 自驱执行并触发下一个 Filter，FilterChain选择的是后者。
FilterChain的执行内部通过 pos 和 n 的位置标记判断是否执行结束。

public class TimeFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("time filter init");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("time filter start");
        long startTime = System.currentTimeMillis();
        // filter内部需要调用filterChain继续执行下一个Filter
        filterChain.doFilter(servletRequest, servletResponse);

        long endTime = System.currentTimeMillis();
        System.out.println("time filter consume " + (endTime - startTime) + " ms");
        System.out.println("time filter end");
    }
}

Tomcat 的 Filter 是通过 filter 对象内部执行filterChain.doFilter来驱动下一个Filter对象的执行。

Tomcat Servlet 的创建

public class StandardWrapper extends ContainerBase
    implements ServletConfig, Wrapper, NotificationEmitter {

    @Override
    public Servlet allocate() throws ServletException {
        boolean newInstance = false;

        // singleThreadModel = false
        if (!singleThreadModel) {
            // instance = DispatcherServlet
            if (instance == null || !instanceInitialized) {
                synchronized (this) {
                    if (instance == null) {
                        try {
                            instance = loadServlet();
                            newInstance = true;
                            if (!singleThreadModel) {
                                countAllocated.incrementAndGet();
                            }
                        } catch (ServletException e) {
                            throw e;
                        } catch (Throwable e) {
                        }
                    }
                    if (!instanceInitialized) {
                        initServlet(instance);
                    }
                }
            }

            if (singleThreadModel) {
                if (newInstance) {
                    synchronized (instancePool) {
                        instancePool.push(instance);
                        nInstances++;
                    }
                }
            } else {
                if (!newInstance) {
                    countAllocated.incrementAndGet();
                }
                // 最终返回的单例
                return instance;
            }
        }

        synchronized (instancePool) {
            while (countAllocated.get() >= nInstances) {
                if (nInstances < maxInstances) {
                    try {
                        instancePool.push(loadServlet());
                        nInstances++;
                    } catch (ServletException e) {
                    } catch (Throwable e) {
                    }
                } else {
                    try {
                        instancePool.wait();
                    } catch (InterruptedException e) {
                        // Ignore
                    }
                }
            }
            countAllocated.incrementAndGet();
            return instancePool.pop();
        }
    }
}

Servlet属于单例实例。

Spring的DispatcherServlet

public abstract class HttpServlet extends GenericServlet {

    private static final long serialVersionUID = 1L;
    private static final String METHOD_DELETE = "DELETE";
    private static final String METHOD_HEAD = "HEAD";
    private static final String METHOD_GET = "GET";
    private static final String METHOD_OPTIONS = "OPTIONS";
    private static final String METHOD_POST = "POST";
    private static final String METHOD_PUT = "PUT";
    private static final String METHOD_TRACE = "TRACE";
    private static final String HEADER_IFMODSINCE = "If-Modified-Since";
    private static final String HEADER_LASTMOD = "Last-Modified";
    private static final String LSTRING_FILE =
        "javax.servlet.http.LocalStrings";
    private static final ResourceBundle lStrings =
        ResourceBundle.getBundle(LSTRING_FILE);

    public HttpServlet() {
    }

    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
    }

    protected void doHead(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {
    }

    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {
    }

    protected void doPut(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {
    }

    protected void doDelete(HttpServletRequest req,
                            HttpServletResponse resp)
        throws ServletException, IOException {
    }


    @Override
    public void service(ServletRequest req, ServletResponse res)
        throws ServletException, IOException {

        HttpServletRequest  request;  // RequestFacade
        HttpServletResponse response;  // ResponseFacade

        try {
            request = (HttpServletRequest) req;
            response = (HttpServletResponse) res;
        } catch (ClassCastException e) {
            throw new ServletException("non-HTTP request or response");
        }
        service(request, response);
    }
}


public abstract class HttpServlet extends GenericServlet {

    protected void service(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {
        String method = req.getMethod();

        if (method.equals(METHOD_GET)) {
            long lastModified = getLastModified(req);
            if (lastModified == -1) {
                doGet(req, resp);
            } else {
                long ifModifiedSince;
                try {
                    ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
                } catch (IllegalArgumentException iae) {
                    ifModifiedSince = -1;
                }
                if (ifModifiedSince < (lastModified / 1000 * 1000)) {
                    maybeSetLastModified(resp, lastModified);
                    doGet(req, resp);
                } else {
                    resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
                }
            }
        } else if (method.equals(METHOD_HEAD)) {
            long lastModified = getLastModified(req);
            maybeSetLastModified(resp, lastModified);
            doHead(req, resp);
        } else if (method.equals(METHOD_POST)) {
            doPost(req, resp);
        } else if (method.equals(METHOD_PUT)) {
            doPut(req, resp);
        } else if (method.equals(METHOD_DELETE)) {
            doDelete(req, resp);
        } else if (method.equals(METHOD_OPTIONS)) {
            doOptions(req,resp);
        } else if (method.equals(METHOD_TRACE)) {
            doTrace(req,resp);
        } else {
        }
    }
}

DispatcherServlet内部通过 method 区分不同的逻辑执行。

public class DispatcherServlet extends FrameworkServlet {

    protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
        
        // 省略代码
        try {
            this.doDispatch(request, response);
        } finally {
        }
    }

    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            try {
                ModelAndView mv = null;
                Object dispatchException = null;

                try {
                    processedRequest = this.checkMultipart(request);
                    multipartRequestParsed = processedRequest != request;
                    mappedHandler = this.getHandler(processedRequest);

                    HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());
                    String method = request.getMethod();
                    // ha = RequestMappingHandlerAdapter，对应的执行对象
                    mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
                    if (asyncManager.isConcurrentHandlingStarted()) {
                        return;
                    }

                    this.applyDefaultViewName(processedRequest, mv);
                    mappedHandler.applyPostHandle(processedRequest, response, mv);
                } catch (Exception var20) {
                } catch (Throwable var21) {
                }

                this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
            } catch (Exception var22) {
            } catch (Throwable var23) {
            }
        } finally {
        }
    }
}

DispatcherServlet的doDispatch通过对应的mappedHandler执行对应的逻辑

public class InvocableHandlerMethod extends HandlerMethod {

    private Object[] getMethodArgumentValues(NativeWebRequest request, ModelAndViewContainer mavContainer,
            Object... providedArgs) throws Exception {

        MethodParameter[] parameters = getMethodParameters();
        Object[] args = new Object[parameters.length];
        for (int i = 0; i < parameters.length; i++) {
            MethodParameter parameter = parameters[i];
            parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
            args[i] = resolveProvidedArgument(parameter, providedArgs);
            if (args[i] != null) {
                continue;
            }
            if (this.argumentResolvers.supportsParameter(parameter)) {
                try {
                    args[i] = this.argumentResolvers.resolveArgument(
                            parameter, mavContainer, request, this.dataBinderFactory);
                    continue;
                }
                catch (Exception ex) {
                }
            }
        }
        return args;
    }
}

public class HandlerMethodArgumentResolverComposite implements HandlerMethodArgumentResolver {

    private final List<HandlerMethodArgumentResolver> argumentResolvers =
            new LinkedList<HandlerMethodArgumentResolver>();
    private final Map<MethodParameter, HandlerMethodArgumentResolver> argumentResolverCache =
            new ConcurrentHashMap<MethodParameter, HandlerMethodArgumentResolver>(256);


    private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
        HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
        if (result == null) {
            for (HandlerMethodArgumentResolver methodArgumentResolver : this.argumentResolvers) {
                if (methodArgumentResolver.supportsParameter(parameter)) {
                    result = methodArgumentResolver;
                    this.argumentResolverCache.put(parameter, result);
                    break;
                }
            }
        }
        return result;
    }
}

DispatcherServlet通过InvocableHandlerMethod类实现不同协议对应的请求参数的解析。

参考

HttpServletRequest参数改写

结合 tomcat 处理流程分析 Filter 的执行

缘起

Tomcat 线程模型

Tomcat 执行流程

Tomcat 监听过程

Tomcat 连接处理过程

Tomcat Socket 注册过程

Tomcat Socket 任务处理过程

Tomcat 请求处理过程

ConnectionHandler处理过程

Http11Processor 处理过程

CoyoteAdapter 执行流程

Tomcat Filter职责链

Tomcat FilterChain创建和释放

Tomcat FilterChain的执行

Tomcat Servlet 的创建

Spring的DispatcherServlet

参考

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