【从入门到放弃-SpringBoot】SpringBoot源码分析-请求过程

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【从入门到放弃-SpringBoot】SpringBoot源码分析-请求过程

aloof_ 2019-06-15 00:09:51 浏览2514

前言

前文【从入门到放弃-SpringBoot】SpringBoot源码分析-WebServer中以SpringBoot中内嵌的Tomcat为例了解了webserver的启动过程。

本文将分析下一条请求在SpringBoot中,从接受到返回都经历了那些过程。

Acceptor


在上文最后的connector启动时,会开始acceptor线程等待接收请求。

Acceptor::run

public void run() {

    int errorDelay = 0;

    // Loop until we receive a shutdown command
    while (endpoint.isRunning()) {

        // Loop if endpoint is paused
        while (endpoint.isPaused() && endpoint.isRunning()) {
            state = AcceptorState.PAUSED;
            try {
                Thread.sleep(50);
            } catch (InterruptedException e) {
                // Ignore
            }
        }

        if (!endpoint.isRunning()) {
            break;
        }
        state = AcceptorState.RUNNING;

        try {
            //if we have reached max connections, wait
            endpoint.countUpOrAwaitConnection();

            // Endpoint might have been paused while waiting for latch
            // If that is the case, don't accept new connections
            if (endpoint.isPaused()) {
                continue;
            }

            U socket = null;
            try {
                // Accept the next incoming connection from the server
                // socket
                socket = endpoint.serverSocketAccept();
            } catch (Exception ioe) {
                // We didn't get a socket
                endpoint.countDownConnection();
                if (endpoint.isRunning()) {
                    // 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 (endpoint.isRunning() && !endpoint.isPaused()) {
                // setSocketOptions() will hand the socket off to
                // an appropriate processor if successful
                if (!endpoint.setSocketOptions(socket)) {
                    endpoint.closeSocket(socket);
                }
            } else {
                endpoint.destroySocket(socket);
            }
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            String msg = sm.getString("endpoint.accept.fail");
            // APR specific.
            // Could push this down but not sure it is worth the trouble.
            if (t instanceof Error) {
                Error e = (Error) t;
                if (e.getError() == 233) {
                    // Not an error on HP-UX so log as a warning
                    // so it can be filtered out on that platform
                    // See bug 50273
                    log.warn(msg, t);
                } else {
                    log.error(msg, t);
                }
            } else {
                    log.error(msg, t);
            }
        }
    }
    state = AcceptorState.ENDED;
}

acceptor会一直监听端口,等待连接

setSocketOptions

@Override
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(sm.getString("endpoint.socketOptionsError"), t);
        } catch (Throwable tt) {
            ExceptionUtils.handleThrowable(tt);
        }
        // Tell to close the socket
        return false;
    }
    return true;
}
  • NioChannel:将捕获到的socket封装成NioChannel

register

public void register(final NioChannel socket) {
    socket.setPoller(this);
    NioSocketWrapper ka = new NioSocketWrapper(socket, NioEndpoint.this);
    socket.setSocketWrapper(ka);
    ka.setPoller(this);
    ka.setReadTimeout(getConnectionTimeout());
    ka.setWriteTimeout(getConnectionTimeout());
    ka.setKeepAliveLeft(NioEndpoint.this.getMaxKeepAliveRequests());
    ka.setSecure(isSSLEnabled());
    PollerEvent r = eventCache.pop();
    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);
}
  • 将channel封装成一个PollerEvent投递到SynchronizedQueue队列中,等待poller进行消费

Poller::run

@Override
public void run() {
    // Loop until destroy() is called
    while (true) {

        boolean hasEvents = false;

        try {
            if (!close) {
                hasEvents = events();
                if (wakeupCounter.getAndSet(-1) > 0) {
                    //if we are here, means we have other stuff to do
                    //do a non blocking select
                    keyCount = selector.selectNow();
                } else {
                    keyCount = selector.select(selectorTimeout);
                }
                wakeupCounter.set(0);
            }
            if (close) {
                events();
                timeout(0, false);
                try {
                    selector.close();
                } catch (IOException ioe) {
                    log.error(sm.getString("endpoint.nio.selectorCloseFail"), ioe);
                }
                break;
            }
        } catch (Throwable x) {
            ExceptionUtils.handleThrowable(x);
            log.error(sm.getString("endpoint.nio.selectorLoopError"), x);
            continue;
        }
        //either we timed out or we woke up, process events first
        if ( keyCount == 0 ) hasEvents = (hasEvents | events());

        Iterator<SelectionKey> iterator =
            keyCount > 0 ? selector.selectedKeys().iterator() : null;
        // Walk through the collection of ready keys and dispatch
        // any active event.
        while (iterator != null && iterator.hasNext()) {
            SelectionKey sk = iterator.next();
            NioSocketWrapper attachment = (NioSocketWrapper)sk.attachment();
            // Attachment may be null if another thread has called
            // cancelledKey()
            if (attachment == null) {
                iterator.remove();
            } else {
                iterator.remove();
                processKey(sk, attachment);
            }
        }//while

        //process timeouts
        timeout(keyCount,hasEvents);
    }//while

    getStopLatch().countDown();
}
  • events:处理队列中的Poller Event,直接调用PollerEvent::run。如果返回true 则说明事件已经被处理,返回false说明队列是空的
  • processKey:请求处理的逻辑,将socket交给processSocket处理。
  • SocketProcessor:继承自SocketProcessorBase,调用run方法开始请求的处理逻辑。


图片来源:https://blog.csdn.net/TVwR8OfV0P/article/details/78851949

SocketProcessorBase的run方法是不是非常眼熟?在【从入门到放弃-MySQL】数据库连接过程分析-客户端中,我们断点调试一次查询请求的处理过程,调用栈入口就是这个方法。

SocketProcessor::run

@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 ) {
            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(sm.getString("endpoint.processing.fail"), t);
        socket.getPoller().cancelledKey(key);
    } finally {
        socketWrapper = null;
        event = null;
        //return to cache
        if (running && !paused) {
            processorCache.push(this);
        }
    }
}
  • 判断socket是否握手完毕并根据socket的状态处理请求或关闭链接
  • ConnectionHandler::process:调用AbstractProcessorLight::process,判断socket的状态及协议是否需要upgrade(如HTTP 2,websocket等基于HTTP的协议),选择对应的Processor处理请求。

Http11Processor::service

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);
    inputBuffer.init(socketWrapper);
    outputBuffer.init(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 && !protocol.isPaused()) {

        // Parsing the request header
        try {
            if (!inputBuffer.parseRequestLine(keptAlive, protocol.getConnectionTimeout(),
                    protocol.getKeepAliveTimeout())) {
                if (inputBuffer.getParsingRequestLinePhase() == -1) {
                    return SocketState.UPGRADING;
                } else if (handleIncompleteRequestLineRead()) {
                    break;
                }
            }

            if (protocol.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(protocol.getMaxHeaderCount());
                if (!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 (!protocol.getDisableUploadTimeout()) {
                    socketWrapper.setReadTimeout(protocol.getConnectionUploadTimeout());
                }
            }
        } catch (IOException e) {
            if (log.isDebugEnabled()) {
                log.debug(sm.getString("http11processor.header.parse"), e);
            }
            setErrorState(ErrorState.CLOSE_CONNECTION_NOW, e);
            break;
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            UserDataHelper.Mode logMode = userDataHelper.getNextMode();
            if (logMode != null) {
                String message = sm.getString("http11processor.header.parse");
                switch (logMode) {
                    case INFO_THEN_DEBUG:
                        message += sm.getString("http11processor.fallToDebug");
                        //$FALL-THROUGH$
                    case INFO:
                        log.info(message, t);
                        break;
                    case DEBUG:
                        log.debug(message, t);
                }
            }
            // 400 - Bad Request
            response.setStatus(400);
            setErrorState(ErrorState.CLOSE_CLEAN, t);
        }

        // Has an upgrade been requested?
        Enumeration<String> connectionValues = request.getMimeHeaders().values("Connection");
        boolean foundUpgrade = false;
        while (connectionValues.hasMoreElements() && !foundUpgrade) {
            foundUpgrade = connectionValues.nextElement().toLowerCase(
                    Locale.ENGLISH).contains("upgrade");
        }

        if (foundUpgrade) {
            // Check the protocol
            String requestedProtocol = request.getHeader("Upgrade");

            UpgradeProtocol upgradeProtocol = protocol.getUpgradeProtocol(requestedProtocol);
            if (upgradeProtocol != null) {
                if (upgradeProtocol.accept(request)) {
                    response.setStatus(HttpServletResponse.SC_SWITCHING_PROTOCOLS);
                    response.setHeader("Connection", "Upgrade");
                    response.setHeader("Upgrade", requestedProtocol);
                    action(ActionCode.CLOSE,  null);
                    getAdapter().log(request, response, 0);

                    InternalHttpUpgradeHandler upgradeHandler =
                            upgradeProtocol.getInternalUpgradeHandler(
                                    socketWrapper, getAdapter(), cloneRequest(request));
                    UpgradeToken upgradeToken = new UpgradeToken(upgradeHandler, null, null);
                    action(ActionCode.UPGRADE, upgradeToken);
                    return SocketState.UPGRADING;
                }
            }
        }

        if (getErrorState().isIoAllowed()) {
            // Setting up filters, and parse some request headers
            rp.setStage(org.apache.coyote.Constants.STAGE_PREPARE);
            try {
                prepareRequest();
            } catch (Throwable t) {
                ExceptionUtils.handleThrowable(t);
                if (log.isDebugEnabled()) {
                    log.debug(sm.getString("http11processor.request.prepare"), t);
                }
                // 500 - Internal Server Error
                response.setStatus(500);
                setErrorState(ErrorState.CLOSE_CLEAN, t);
            }
        }

        int maxKeepAliveRequests = protocol.getMaxKeepAliveRequests();
        if (maxKeepAliveRequests == 1) {
            keepAlive = false;
        } else if (maxKeepAliveRequests > 0 &&
                socketWrapper.decrementKeepAlive() <= 0) {
            keepAlive = false;
        }

        // Process the request in the adapter
        if (getErrorState().isIoAllowed()) {
            try {
                rp.setStage(org.apache.coyote.Constants.STAGE_SERVICE);
                getAdapter().service(request, response);
                // Handle when the response was committed before a serious
                // error occurred.  Throwing a ServletException should both
                // set the status to 500 and set the errorException.
                // If we fail here, then the response is likely already
                // committed, so we can't try and set headers.
                if(keepAlive && !getErrorState().isError() && !isAsync() &&
                        statusDropsConnection(response.getStatus())) {
                    setErrorState(ErrorState.CLOSE_CLEAN, null);
                }
            } catch (InterruptedIOException e) {
                setErrorState(ErrorState.CLOSE_CONNECTION_NOW, e);
            } catch (HeadersTooLargeException e) {
                log.error(sm.getString("http11processor.request.process"), e);
                // The response should not have been committed but check it
                // anyway to be safe
                if (response.isCommitted()) {
                    setErrorState(ErrorState.CLOSE_NOW, e);
                } else {
                    response.reset();
                    response.setStatus(500);
                    setErrorState(ErrorState.CLOSE_CLEAN, e);
                    response.setHeader("Connection", "close"); // TODO: Remove
                }
            } catch (Throwable t) {
                ExceptionUtils.handleThrowable(t);
                log.error(sm.getString("http11processor.request.process"), t);
                // 500 - Internal Server Error
                response.setStatus(500);
                setErrorState(ErrorState.CLOSE_CLEAN, t);
                getAdapter().log(request, response, 0);
            }
        }

        // Finish the handling of the request
        rp.setStage(org.apache.coyote.Constants.STAGE_ENDINPUT);
        if (!isAsync()) {
            // If this is an async request then the request ends when it has
            // been completed. The AsyncContext is responsible for calling
            // endRequest() in that case.
            endRequest();
        }
        rp.setStage(org.apache.coyote.Constants.STAGE_ENDOUTPUT);

        // If there was an error, make sure the request is counted as
        // and error, and update the statistics counter
        if (getErrorState().isError()) {
            response.setStatus(500);
        }

        if (!isAsync() || getErrorState().isError()) {
            request.updateCounters();
            if (getErrorState().isIoAllowed()) {
                inputBuffer.nextRequest();
                outputBuffer.nextRequest();
            }
        }

        if (!protocol.getDisableUploadTimeout()) {
            int connectionTimeout = protocol.getConnectionTimeout();
            if(connectionTimeout > 0) {
                socketWrapper.setReadTimeout(connectionTimeout);
            } else {
                socketWrapper.setReadTimeout(0);
            }
        }

        rp.setStage(org.apache.coyote.Constants.STAGE_KEEPALIVE);

        sendfileState = processSendfile(socketWrapper);
    }

    rp.setStage(org.apache.coyote.Constants.STAGE_ENDED);

    if (getErrorState().isError() || protocol.isPaused()) {
        return SocketState.CLOSED;
    } else if (isAsync()) {
        return SocketState.LONG;
    } else if (isUpgrade()) {
        return SocketState.UPGRADING;
    } else {
        if (sendfileState == SendfileState.PENDING) {
            return SocketState.SENDFILE;
        } else {
            if (openSocket) {
                if (readComplete) {
                    return SocketState.OPEN;
                } else {
                    return SocketState.LONG;
                }
            } else {
                return SocketState.CLOSED;
            }
        }
    }
}
  • 初始化各项配置及初始值
  • 解析request的header信息,判断是否是upgrade协议,是的话设置http header信息
  • prepareRequest:校验协议、校验header(如user-agent、Connection、host等)设置filters
  • getAdapter().service:getAdapter获取的是在Connector::initInternal中设置的CoyoteAdapter

CoyoteAdapter::service

public void service(org.apache.coyote.Request req, org.apache.coyote.Response res)
            throws Exception {

    Request request = (Request) req.getNote(ADAPTER_NOTES);
    Response response = (Response) res.getNote(ADAPTER_NOTES);

    if (request == null) {
        // Create objects
        request = connector.createRequest();
        request.setCoyoteRequest(req);
        response = connector.createResponse();
        response.setCoyoteResponse(res);

        // Link objects
        request.setResponse(response);
        response.setRequest(request);

        // Set as notes
        req.setNote(ADAPTER_NOTES, request);
        res.setNote(ADAPTER_NOTES, response);

        // Set query string encoding
        req.getParameters().setQueryStringCharset(connector.getURICharset());
    }

    if (connector.getXpoweredBy()) {
        response.addHeader("X-Powered-By", POWERED_BY);
    }

    boolean async = false;
    boolean postParseSuccess = false;

    req.getRequestProcessor().setWorkerThreadName(THREAD_NAME.get());

    try {
        // Parse and set Catalina and configuration specific
        // request parameters
        postParseSuccess = postParseRequest(req, request, res, response);
        if (postParseSuccess) {
            //check valves if we support async
            request.setAsyncSupported(
                    connector.getService().getContainer().getPipeline().isAsyncSupported());
            // Calling the container
            connector.getService().getContainer().getPipeline().getFirst().invoke(
                    request, response);
        }
        if (request.isAsync()) {
            async = true;
            ReadListener readListener = req.getReadListener();
            if (readListener != null && request.isFinished()) {
                // Possible the all data may have been read during service()
                // method so this needs to be checked here
                ClassLoader oldCL = null;
                try {
                    oldCL = request.getContext().bind(false, null);
                    if (req.sendAllDataReadEvent()) {
                        req.getReadListener().onAllDataRead();
                    }
                } finally {
                    request.getContext().unbind(false, oldCL);
                }
            }

            Throwable throwable =
                    (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION);

            // If an async request was started, is not going to end once
            // this container thread finishes and an error occurred, trigger
            // the async error process
            if (!request.isAsyncCompleting() && throwable != null) {
                request.getAsyncContextInternal().setErrorState(throwable, true);
            }
        } else {
            request.finishRequest();
            response.finishResponse();
        }

    } catch (IOException e) {
        // Ignore
    } finally {
        AtomicBoolean error = new AtomicBoolean(false);
        res.action(ActionCode.IS_ERROR, error);

        if (request.isAsyncCompleting() && error.get()) {
            // Connection will be forcibly closed which will prevent
            // completion happening at the usual point. Need to trigger
            // call to onComplete() here.
            res.action(ActionCode.ASYNC_POST_PROCESS,  null);
            async = false;
        }

        // Access log
        if (!async && postParseSuccess) {
            // Log only if processing was invoked.
            // If postParseRequest() failed, it has already logged it.
            Context context = request.getContext();
            Host host = request.getHost();
            // If the context is null, it is likely that the endpoint was
            // shutdown, this connection closed and the request recycled in
            // a different thread. That thread will have updated the access
            // log so it is OK not to update the access log here in that
            // case.
            // The other possibility is that an error occurred early in
            // processing and the request could not be mapped to a Context.
            // Log via the host or engine in that case.
            long time = System.currentTimeMillis() - req.getStartTime();
            if (context != null) {
                context.logAccess(request, response, time, false);
            } else if (response.isError()) {
                if (host != null) {
                    host.logAccess(request, response, time, false);
                } else {
                    connector.getService().getContainer().logAccess(
                            request, response, time, false);
                }
            }
        }

        req.getRequestProcessor().setWorkerThreadName(null);

        // Recycle the wrapper request and response
        if (!async) {
            updateWrapperErrorCount(request, response);
            request.recycle();
            response.recycle();
        }
    }
}
  • 初始化request和response,如果没有则新new
  • postParseRequest:保证在header解析后的request能被Container正常解析、使用。比如权限认证、字符编码、版本、session等的转换和校验
  • invoke:逐级调用StandardEngineValve、StandardHostValve、StandardHostValve、StandardWrapperValve的invoke实现
  • doFilter:StandardWrapperValve调用doFilter,会执行定义的Filter过滤器,执行完毕后执行HttpServlet::service

HttpServlet::service

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) {
            // servlet doesn't support if-modified-since, no reason
            // to go through further expensive logic
            doGet(req, resp);
        } else {
            long ifModifiedSince;
            try {
                ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
            } catch (IllegalArgumentException iae) {
                // Invalid date header - proceed as if none was set
                ifModifiedSince = -1;
            }
            if (ifModifiedSince < (lastModified / 1000 * 1000)) {
                // If the servlet mod time is later, call doGet()
                // Round down to the nearest second for a proper compare
                // A ifModifiedSince of -1 will always be less
                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 {
        //
        // Note that this means NO servlet supports whatever
        // method was requested, anywhere on this server.
        //

        String errMsg = lStrings.getString("http.method_not_implemented");
        Object[] errArgs = new Object[1];
        errArgs[0] = method;
        errMsg = MessageFormat.format(errMsg, errArgs);

        resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
    }
}
  • 根据请求的method做对应的处理逻辑,其实doXXX底层都是调用的SpringMVC的FrameworkServlet::processRequest
  • FrameworkServlet::processRequest对request做简单处理后,调用了doService,实现类为DispatcherServlet

DispatcherServlet::doService

@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
    logRequest(request);

    // Keep a snapshot of the request attributes in case of an include,
    // to be able to restore the original attributes after the include.
    Map<String, Object> attributesSnapshot = null;
    if (WebUtils.isIncludeRequest(request)) {
        attributesSnapshot = new HashMap<>();
        Enumeration<?> attrNames = request.getAttributeNames();
        while (attrNames.hasMoreElements()) {
            String attrName = (String) attrNames.nextElement();
            if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
                attributesSnapshot.put(attrName, request.getAttribute(attrName));
            }
        }
    }

    // Make framework objects available to handlers and view objects.
    request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
    request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
    request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
    request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());

    if (this.flashMapManager != null) {
        FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
        if (inputFlashMap != null) {
            request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
        }
        request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
        request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
    }

    try {
        doDispatch(request, response);
    }
    finally {
        if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
            // Restore the original attribute snapshot, in case of an include.
            if (attributesSnapshot != null) {
                restoreAttributesAfterInclude(request, attributesSnapshot);
            }
        }
    }
}
  • 主要调用方法为doDispatch

DispatcherServlet::doDispatch

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

    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

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

        try {
            processedRequest = checkMultipart(request);
            multipartRequestParsed = (processedRequest != request);

            // Determine handler for the current request.
            mappedHandler = getHandler(processedRequest);
            if (mappedHandler == null) {
                noHandlerFound(processedRequest, response);
                return;
            }

            // Determine handler adapter for the current request.
            HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

            // Process last-modified header, if supported by the handler.
            String method = request.getMethod();
            boolean isGet = "GET".equals(method);
            if (isGet || "HEAD".equals(method)) {
                long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                    return;
                }
            }

            if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                return;
            }

            // Actually invoke the handler.
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

            if (asyncManager.isConcurrentHandlingStarted()) {
                return;
            }

            applyDefaultViewName(processedRequest, mv);
            mappedHandler.applyPostHandle(processedRequest, response, mv);
        }
        catch (Exception ex) {
            dispatchException = ex;
        }
        catch (Throwable err) {
            // As of 4.3, we're processing Errors thrown from handler methods as well,
            // making them available for @ExceptionHandler methods and other scenarios.
            dispatchException = new NestedServletException("Handler dispatch failed", err);
        }
        processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
    }
    catch (Exception ex) {
        triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
    }
    catch (Throwable err) {
        triggerAfterCompletion(processedRequest, response, mappedHandler,
                new NestedServletException("Handler processing failed", err));
    }
    finally {
        if (asyncManager.isConcurrentHandlingStarted()) {
            // Instead of postHandle and afterCompletion
            if (mappedHandler != null) {
                mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
            }
        }
        else {
            // Clean up any resources used by a multipart request.
            if (multipartRequestParsed) {
                cleanupMultipart(processedRequest);
            }
        }
    }
}
  • getHandler:根据requestURI通过HandlerMapping(这里是requestMappingHandlerMapping)获取到处理此请求的handler以及拦截器(requestMapping对应的类和方法)
  • getHandlerAdapter:获取能执行这个Handler的Adapter
  • applyPreHandle:处理拦截器的前置拦截。
  • ha.handle:通过获取到的Adapter(这里是RequestMappingHandlerAdapter)执行Controller方法,得到ModelAndView
  • processDispatchResult:直接调用render方法,将返回的ModelAndView交给ViewResolver视图解析器找到指定的视图(view),赋值给response返回给客户端显示。

RequestMappingHandlerAdapter::handleInternal

protected ModelAndView handleInternal(HttpServletRequest request,
        HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

    ModelAndView mav;
    checkRequest(request);

    // Execute invokeHandlerMethod in synchronized block if required.
    if (this.synchronizeOnSession) {
        HttpSession session = request.getSession(false);
        if (session != null) {
            Object mutex = WebUtils.getSessionMutex(session);
            synchronized (mutex) {
                mav = invokeHandlerMethod(request, response, handlerMethod);
            }
        }
        else {
            // No HttpSession available -> no mutex necessary
            mav = invokeHandlerMethod(request, response, handlerMethod);
        }
    }
    else {
        // No synchronization on session demanded at all...
        mav = invokeHandlerMethod(request, response, handlerMethod);
    }

    if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
        if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
            applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
        }
        else {
            prepareResponse(response);
        }
    }

    return mav;
}
  • invokeHandlerMethod:执行Handler方法获取到ModelAndView,调用ServletInvocableHandlerMethod::invokeAndHandle

ServletInvocableHandlerMethod::invokeAndHandle

public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
        Object... providedArgs) throws Exception {

    Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
    setResponseStatus(webRequest);

    if (returnValue == null) {
        if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
            mavContainer.setRequestHandled(true);
            return;
        }
    }
    else if (StringUtils.hasText(getResponseStatusReason())) {
        mavContainer.setRequestHandled(true);
        return;
    }

    mavContainer.setRequestHandled(false);
    Assert.state(this.returnValueHandlers != null, "No return value handlers");
    try {
        this.returnValueHandlers.handleReturnValue(
                returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
    }
    catch (Exception ex) {
        if (logger.isTraceEnabled()) {
            logger.trace(formatErrorForReturnValue(returnValue), ex);
        }
        throw ex;
    }
}
  • invokeForRequest: 调用InvocableHandlerMethod::doInvoke 通过反射的方式执行requestMapping对应的Controller方法
  • this.returnValueHandlers.handleReturnValue:将执行完的returnValue设置到response中,我们常用的json返回值就是在这里设置的。

总结

通过对源码的分析我们了解了请求在Tomcat中的流转情况,以及SpringMVC如何完成一个请求的处理。
一个请求在SpringMVC中的生命周期如下图所示:

1、用户发送请求,浏览器acceptor监听到请求,投递至PollerEvent队列,Poller进行消费,交给SocketProcessor(DispatcherServlet)处理。

2、分发器DispatcherServlet向映射器HandlerMapping发请求,根据requestURL获取Handler

3、映射器返回HandlerExecutionChain,包含了需要处理的Handler及HandlerInterceptor拦截器

4、根据Handler获取对应的适配器

5、适配器执行具体的Handler(即Controller的方法)

6、Handler执行完返回ModelAndModel

7、HandlerAdapter将ModelAndModel返回给分发器DispatcherServlet

8、DispatcherServlet将ModelAndView传给ViewReslover视图解析器

9、ViewReslover解析后返回具体的View模板

10、渲染视图,将数据填充至视图中

11、将渲染好的视图返回给用户,在浏览器客户端展现

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