在使用 Tomcat 的时候，我们只需要在 Servlet 实现类中写我们的业务逻辑代码即可，不需要管 Socket 连接、协议处理要怎么实现，因为这部分作为不经常变动的部分，被封装到了 Tomcat 中，程序员只需要引入 Tomcat 中即可，这也是面向对象编程的经典实践。
那么 Tomcat 中的一次请求都要经过哪些类的处理呢？以及 Tomcat 在处理的时候做了哪些方面的考量和设计呢？
Connector
我们知道，Tomcat 中的 Connector 组件负责 Socket 连接的创建和管理，以及网络字节流的传输。在 Connector 组件中，有三个组件 Endpoint、Processor、Adapt。
- Endpoint：负责 ServerSocket 的创建和循环获取 Socket 连接
- Processor：根据具体的协议，解析字节流中的数据
- Adapt：将 Tomcat Request 转换成 ServletRequest，将 ServletResponse 转换成 Tomcat Response
Tomcat 的设计者将 Endpoint 和 Processor 又做了一次封装，将它们封装在 ProtocolHandler 中，表示协议处理器。
从上面看，请求会先在 Endpoint 对象中被接受，然后在 Processor 中被解析，最后通过 Adapt 转换后发送给 Servlet 容器。
Endpoint
NioEndpoint#startInternal
生命周期方法，在启动 Tomcat 的时候会调用 Server#start -> Service.start -> Connector.start -> ProtocolHandler.start() -> EndPoint.start() -> Endpoint.startInternal()
java
@Override
public void startInternal() throws Exception {
if (!running) {
running = true;
paused = false;
if (socketProperties.getProcessorCache() != 0) {
processorCache = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
socketProperties.getProcessorCache());
}
if (socketProperties.getEventCache() != 0) {
eventCache = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
socketProperties.getEventCache());
}
if (socketProperties.getBufferPool() != 0) {
nioChannels = new SynchronizedStack<>(SynchronizedStack.DEFAULT_SIZE,
socketProperties.getBufferPool());
}
// Create worker collection
if (getExecutor() == null) {
createExecutor();
}
initializeConnectionLatch();
// Start poller thread
// 启动一个 Poller 线程并赋值给 NioEndpoint 的 poller 成员变量
// 这个变量在后续处理 PollerEvent 的时候会用到
poller = new Poller();
Thread pollerThread = new Thread(poller, getName() + "-Poller");
pollerThread.setPriority(threadPriority);
pollerThread.setDaemon(true);
pollerThread.start();
// 启动 Acceptor 线程
startAcceptorThread();
}
}AbstractEndpoint#startAcceptorThread
创建并启动 Acceptor 线程
java
protected void startAcceptorThread() {
acceptor = new Acceptor<>(this);
String threadName = getName() + "-Acceptor";
acceptor.setThreadName(threadName);
Thread t = new Thread(acceptor, threadName);
t.setPriority(getAcceptorThreadPriority());
t.setDaemon(getDaemon());
t.start();
}Acceptor#run
Acceptor 的 run 方法中循环获取 socket 连接，为了减少篇幅和方便阅读，我简化了代码：
java
public void run() {
int errorDelay = 0;
long pauseStart = 0;
try {
// 循环，直到我们接收到一个 shutdown 命令
while (!stopCalled) {
if (stopCalled) {
break;
}
state = AcceptorState.RUNNING;
try {
// 如果我们到达了最大连接数，则阻塞该线程
endpoint.countUpOrAwaitConnection();
if (endpoint.isPaused()) {
continue;
}
U socket = null;
try {
// 获取 socket 连接
socket = endpoint.serverSocketAccept();
} catch (Exception ioe) {
...
}
// Successful accept, reset the error delay
errorDelay = 0;
if (!stopCalled && !endpoint.isPaused()) {
// setSocketOptions() 方法会把 socket 交给合适的 processor 处理
if (!endpoint.setSocketOptions(socket)) {
endpoint.closeSocket(socket);
}
} else {
endpoint.destroySocket(socket);
}
} catch (Throwable t) {
...
}
}
} finally {
stopLatch.countDown();
}
state = AcceptorState.ENDED;
}NioEndpoint#setSocketOptions
这里主要做了三件事：
- 设置 socket 为非阻塞模式
- 将 socket 封装到 NioSocketWrapper 中
- 将 NioSocketWrapper 注册到 Poller 中
其中 NioSocketWrapper 是 NioEndpoint 的静态内部类，Poller 是 NioEndpoint 的内部类，它实现了 Runnable 接口。
java
@Override
protected boolean setSocketOptions(SocketChannel socket) {
NioSocketWrapper socketWrapper = null;
try {
// Allocate channel and wrapper
NioChannel channel = null;
if (nioChannels != null) {
channel = nioChannels.pop();
}
if (channel == null) {
SocketBufferHandler bufhandler = new SocketBufferHandler(
socketProperties.getAppReadBufSize(),
socketProperties.getAppWriteBufSize(),
socketProperties.getDirectBuffer());
if (isSSLEnabled()) {
channel = new SecureNioChannel(bufhandler, this);
} else {
channel = new NioChannel(bufhandler);
}
}
// NioSocketWrapper 是 NioEndpoint 的静态内部类
// 将 socket 封装到 NioSocketWrapper 中
NioSocketWrapper newWrapper = new NioSocketWrapper(channel, this);
channel.reset(socket, newWrapper);
connections.put(socket, newWrapper);
socketWrapper = newWrapper;
// 设置 socket 为非阻塞模式
socket.configureBlocking(false);
socketProperties.setProperties(socket.socket());
socketWrapper.setReadTimeout(getConnectionTimeout());
socketWrapper.setWriteTimeout(getConnectionTimeout());
socketWrapper.setKeepAliveLeft(NioEndpoint.this.getMaxKeepAliveRequests());
// Poller 是 NioEndpoint 的内部类，它实现了 Runnable 接口
poller.register(socketWrapper);
return true;
} catch (Throwable t) {
...
}
// Tell to close the socket if needed
return false;
}Poller#register -> Poller#addEvent
- 在 NioSocketWrapper 中设置感兴趣的事件是 SelectionKey.OP_READ，也就是读事件，此时还没有注册到 Selector 上
- 将 NioSocketWrapper 封装成 PollerEvent，并添加到 Poller 持有的同步队列中
java
/**
* Registers a newly created socket with the poller.
*
* @param socketWrapper The socket wrapper
*/
public void register(final NioSocketWrapper socketWrapper) {
// 设置感兴趣的事件是读事件
socketWrapper.interestOps(SelectionKey.OP_READ);//this is what OP_REGISTER turns into.
// 将 NioSocketWrapper 封装成 PollerEvent
PollerEvent pollerEvent = createPollerEvent(socketWrapper, OP_REGISTER);
addEvent(pollerEvent);
}
private void addEvent(PollerEvent event) {
// 将 PollerEvent 添加到 Poller 中 Tomcat 自定义的同步队列中
events.offer(event);
if (wakeupCounter.incrementAndGet() == 0) {
selector.wakeup();
}
}Poller#run
Poller 线程在一个死循环中，首先通过 events() 方法，将 PollerEvent 同步队列中的 socket 用持有的 Selector 注册感兴趣的事件。
然后获取准备好的通道， 每一个通道都传入 processKey 方法中
java
@Override
public void run() {
// Loop until destroy() is called
while (true) {
boolean hasEvents = false;
try {
if (!close) {
hasEvents = events();
if (wakeupCounter.getAndSet(-1) > 0) {
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;
}
// Either we timed out or we woke up, process events first
if (keyCount == 0) {
hasEvents = (hasEvents | events());
}
} catch (Throwable x) {
ExceptionUtils.handleThrowable(x);
log.error(sm.getString("endpoint.nio.selectorLoopError"), x);
continue;
}
Iterator<SelectionKey> iterator =
keyCount > 0 ? selector.selectedKeys().iterator() : null;
// 如果 Selector 存在已经准备好的通道，则遍历就绪的通道集
while (iterator != null && iterator.hasNext()) {
SelectionKey sk = iterator.next();
iterator.remove();
NioSocketWrapper socketWrapper = (NioSocketWrapper) sk.attachment();
if (socketWrapper != null) {
processKey(sk, socketWrapper);
}
}
// Process timeouts
timeout(keyCount,hasEvents);
}
getStopLatch().countDown();
}Poller#events
java
public boolean events() {
boolean result = false;
PollerEvent pe = null;
for (int i = 0, size = events.size(); i < size && (pe = events.poll()) != null; i++ ) {
// 遍历存储 PollerEvent 的同步队列，如果队列大于零，则设置返回值 result 为 true
result = true;
NioSocketWrapper socketWrapper = pe.getSocketWrapper();
SocketChannel sc = socketWrapper.getSocket().getIOChannel();
int interestOps = pe.getInterestOps();
if (sc == null) {
log.warn(sm.getString("endpoint.nio.nullSocketChannel"));
socketWrapper.close();
} else if (interestOps == OP_REGISTER) {
try {
sc.register(getSelector(), SelectionKey.OP_READ, socketWrapper);
} catch (Exception x) {
log.error(sm.getString("endpoint.nio.registerFail"), x);
}
} else {
// 当前 socketChannel 是否在 selector 中注册
final SelectionKey key = sc.keyFor(getSelector());
if (key == null) {
socketWrapper.close();
} else {
final NioSocketWrapper attachment = (NioSocketWrapper) key.attachment();
if (attachment != null) {
try {
int ops = key.interestOps() | interestOps;
attachment.interestOps(ops);
// 在 selector 上注册 READ 事件，每个 Poller 都会创建一个单独的 Selector
key.interestOps(ops);
} catch (CancelledKeyException ckx) {
cancelledKey(key, socketWrapper);
}
} else {
cancelledKey(key, socketWrapper);
}
}
}
if (running && eventCache != null) {
// 重置 PollerEvent 并放回缓存 PollerEvent 的同步栈中
pe.reset();
eventCache.push(pe);
}
}
return result;
}Poller#processKey
该方法的核心逻辑是做条件判断，通过判断 socket 准备好的事件的类型，调用不同的方法来处理。如果是读事件，最终会走到 processSocket(socketWrapper, SocketEvent.OPEN_READ, true) 。
java
protected void processKey(SelectionKey sk, NioSocketWrapper socketWrapper) {
try {
if (close) {
cancelledKey(sk, socketWrapper);
} else if (sk.isValid()) {
if (sk.isReadable() || sk.isWritable()) {
if (socketWrapper.getSendfileData() != null) {
processSendfile(sk, socketWrapper, false);
} else {
unreg(sk, socketWrapper, sk.readyOps());
boolean closeSocket = false;
// Read goes before write
if (sk.isReadable()) {
if (socketWrapper.readOperation != null) {
if (!socketWrapper.readOperation.process()) {
closeSocket = true;
}
} else if (socketWrapper.readBlocking) {
synchronized (socketWrapper.readLock) {
socketWrapper.readBlocking = false;
socketWrapper.readLock.notify();
}
} else if (!processSocket(socketWrapper, SocketEvent.OPEN_READ, true)) {
closeSocket = true;
}
}
if (!closeSocket && sk.isWritable()) {
if (socketWrapper.writeOperation != null) {
if (!socketWrapper.writeOperation.process()) {
closeSocket = true;
}
} else if (socketWrapper.writeBlocking) {
synchronized (socketWrapper.writeLock) {
socketWrapper.writeBlocking = false;
socketWrapper.writeLock.notify();
}
} else if (!processSocket(socketWrapper, SocketEvent.OPEN_WRITE, true)) {
closeSocket = true;
}
}
if (closeSocket) {
cancelledKey(sk, socketWrapper);
}
}
}
} else {
// Invalid key
cancelledKey(sk, socketWrapper);
}
} catch (CancelledKeyException ckx) {
cancelledKey(sk, socketWrapper);
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
log.error(sm.getString("endpoint.nio.keyProcessingError"), t);
}
}Poller#processSocket
该方法用来将 NioSocketWrapper 封装到 SocketProcessor 中，SocketProcessor 是 NioEndpoint 的内部类，它实现了 Runnable 接口，创建好 SocketProcessor 之后将它放到 executor 线程池中执行。
java
public boolean processSocket(SocketWrapperBase<S> socketWrapper,
SocketEvent event, boolean dispatch) {
try {
if (socketWrapper == null) {
return false;
}
SocketProcessorBase<S> sc = null;
if (processorCache != null) {
sc = processorCache.pop();
}
if (sc == null) {
sc = createSocketProcessor(socketWrapper, event);
} else {
sc.reset(socketWrapper, event);
}
Executor executor = getExecutor();
if (dispatch && executor != null) {
executor.execute(sc);
} else {
sc.run();
}
} catch (RejectedExecutionException ree) {
getLog().warn(sm.getString("endpoint.executor.fail", socketWrapper) , ree);
return false;
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
// This means we got an OOM or similar creating a thread, or that
// the pool and its queue are full
getLog().error(sm.getString("endpoint.process.fail"), t);
return false;
}
return true;
}SocketProcessor#doRun
前面我们说过 Connector 组件中包含了 Endpoint、Processor 和 Adapt 三个组件，三个组件各司其职完成了 Socket 客户端的连接、网络字节流的解析和 Request 和 Response 对象的转换。
在 SocketProcessor 线程会调用 Processor 组件的 process 方法来根据不同的协议解析字节流。
java
@Override
protected void doRun() {
boolean launch = false;
try {
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 and pool
socketWrapper.close();
} else if (state == SocketState.UPGRADING) {
launch = true;
}
} catch (VirtualMachineError vme) {
ExceptionUtils.handleThrowable(vme);
} catch (Throwable t) {
log.error(sm.getString("endpoint.processing.fail"), t);
if (socketWrapper != null) {
((Nio2SocketWrapper) socketWrapper).close();
}
} finally {
...
}
}AbstractProtocol#process
调用 AbstractProcessLight 类的 process 方法
java
@Override
public SocketState process(SocketWrapperBase<S> wrapper, SocketEvent status) {
if (wrapper == null) {
// Nothing to do. Socket has been closed.
return SocketState.CLOSED;
}
S socket = wrapper.getSocket();
Processor processor = (Processor) wrapper.takeCurrentProcessor();
try {
...
processor.setSslSupport(
wrapper.getSslSupport(getProtocol().getClientCertProvider()));
SocketState state = SocketState.CLOSED;
do {
// 调用 AbstractProcessLight 类的 process 方法
state = processor.process(wrapper, status);
...
} while ( state == SocketState.UPGRADING);
...
if (processor != null) {
wrapper.setCurrentProcessor(processor);
}
return state;
} catch(java.net.SocketException e) {
...
}
// Make sure socket/processor is removed from the list of current
// connections
release(processor);
return SocketState.CLOSED;
}AbstractProcessLight#process
该方法主要做一些条件判断，如果我们的请求是一个简单的 GET 请求，则会执行到 state = service(socketWrapper); 这行代码。
java
@Override
public SocketState process(SocketWrapperBase<?> socketWrapper, SocketEvent status)
throws IOException {
SocketState state = SocketState.CLOSED;
Iterator<DispatchType> dispatches = null;
do {
if (dispatches != null) {
DispatchType nextDispatch = dispatches.next();
if (getLog().isDebugEnabled()) {
getLog().debug("Processing dispatch type: [" + nextDispatch + "]");
}
state = dispatch(nextDispatch.getSocketStatus());
if (!dispatches.hasNext()) {
state = checkForPipelinedData(state, socketWrapper);
}
} else if (status == SocketEvent.DISCONNECT) {
// Do nothing here, just wait for it to get recycled
} else if (isAsync() || isUpgrade() || state == SocketState.ASYNC_END) {
state = dispatch(status);
state = checkForPipelinedData(state, socketWrapper);
} else if (status == SocketEvent.OPEN_WRITE) {
// Extra write event likely after async, ignore
state = SocketState.LONG;
} else if (status == SocketEvent.OPEN_READ) {
// 读事件
state = service(socketWrapper);
} else if (status == SocketEvent.CONNECT_FAIL) {
logAccess(socketWrapper);
} else {
state = SocketState.CLOSED;
}
...
} while (state == SocketState.ASYNC_END ||
dispatches != null && state != SocketState.CLOSED);
return state;
}Http11Processor#service
Http11Processor 类是 HTTP/1.1 协议的实现，这里会按照请求行、请求头、请求体的顺序解析字节流。
因为代码太多，这里不做展示，请求最终会调用 CoyoteAdapter#service，CoyoteAdapter 是 Adapter 的实现类，它属于 Connector 组件中的 Adapter 组件，用于完成 Request 和 Response 对象的适配工作，并调用 Container 的 Pipeline，至此请求进入到 Servlet 容器中。
java
@Override
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);
...
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);
}
...
} catch (IOException e) {
// Ignore
} finally {
...
}
}总结
简单的梳理了 HTTP 请求进入 Tomcat 的代码调用栈之后，我们可以通过上面的流程画出请求的流程图：
Http11Processor 中主要是对 HTTP 协议的实现，相比于这部分，我对 Endpoint 中的处理更感兴趣，因为这部分更接近操作系统，这里我们只讨论了 Endpoint 在 NIO 模式下的处理流程，在使用 NIO 模式的时候，Tomcat 做了哪些设计和努力来让 Tomcat 能够支持高并发呢？
随着 Tomcat 版本的不断更新，每个版本都会对这部分做一些小优化，该篇文章我用的 Tomcat 是 8.5.84 的版本，其中 Endpoint 中的 Acceptor 和 Poller 都只开启了一个线程，在之后的版本中改成了可以开启多个线程，增加线程可以提高吞吐量。
Container
在上节讲解 Connector 组件的时候我们了解到，Connector 最终会调用到 CoyoteAdapter#service 方法，该方法会通过 Engine 的 Pipeline 将请求发送给 Servlet 容器。
CoyoteAdapter#service
java
@Override
public void service(org.apache.coyote.Request req, org.apache.coyote.Response res)
throws Exception {
...
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);
}
...
} catch (IOException e) {
// Ignore
} finally {
...
}
}在 Servlet 容器中，组件被组织成具有层次结构，大容器包小容器，最小的容器就是 Servlet，Engine -> Host -> Context -> Wrapper。每个容器组件都实现了 Container 接口，且都持有 Pipeline 对象，Pipeline 和 Valve 组合形成了责任链模式。
Pipeline 持有链路中第一个 First Valve 和最后一个 Basic Valve，每个 Valve 持有下一个 Valve 的应用，每个容器在初始化的时候会给 Pipeline 配置好 Basic Valve，每个 Pipeline 的 Basic Valve 会调用子容器 Pipeline 的 First Valve，于是请求就可以在容器中流转。
我们启动本地的 Tomcat，并发起一个 GET 请求，在 IDEA 中 debug 看在默认配置下各容器都持有哪些 Valve。
首先请求会到 StandardEngine，可以看出持有的是 StandardPipeline，它没有 First Valve，只有 Basic Valve，所以它只有一个 Valve，在该 Valve 中完成请求的转发。
之后请求到 StandardHost，它的 StandardPipeline 中既有 First Valve 也有 Basic Valve，Pipeline 中整个责任链如下：
-
NonLoginAuthenticator
-
StandardContextValve
之后请求到 StandardHost，它的 StandardPipeline 也只有一个 Basic Valve。
最后是 StandardWrapper，它的 StandardPipeline 也只有一个 Basic Valve。
StandardWrapperValve
有上可知，StandardWrapperValve 应该是最后一个 Valve 了，再之后就是 Servlet 了。这里单独拿出来细究是怎么到 Servlet 的 service 方法的。
java
@Override
public final void invoke(Request request, Response response)
throws IOException, ServletException {
...
// Allocate a servlet instance to process this request
try {
if (!unavailable) {
// 实例化 Servlet，Servlet 是延迟实例化的，只有用到了才会实例化，在实例化的时候会调用 Servlet 的 init 方法
servlet = wrapper.allocate();
}
} catch (UnavailableException e) {
...
}
...
// Create the filter chain for this request
// 为该请求创建 filterChain
ApplicationFilterChain filterChain =
ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);
// Call the filter chain for this request
// NOTE: This also calls the servlet's service() method
Container container = this.container;
try {
if ((servlet != null) && (filterChain != null)) {
// Swallow output if needed
if (context.getSwallowOutput()) {
try {
SystemLogHandler.startCapture();
if (request.isAsyncDispatching()) {
request.getAsyncContextInternal().doInternalDispatch();
} else {
// 触发过滤器链
filterChain.doFilter(request.getRequest(),
response.getResponse());
}
} finally {
String log = SystemLogHandler.stopCapture();
if (log != null && log.length() > 0) {
context.getLogger().info(log);
}
}
} else {
if (request.isAsyncDispatching()) {
request.getAsyncContextInternal().doInternalDispatch();
} else {
// 触发过滤器链
filterChain.doFilter
(request.getRequest(), response.getResponse());
}
}
}
} catch (ClientAbortException | CloseNowException e) {
...
} finally {
// 释放资源
...
}
}由代码可知会先创建一个 filterChain，servlet 就是在这里面被调用的，我们继续看创建 filterChain 的方法。
java
public static ApplicationFilterChain createFilterChain(ServletRequest request,
Wrapper wrapper, Servlet servlet) {
// If there is no servlet to execute, return null
if (servlet == null) {
return null;
}
// Create and initialize a filter chain object
ApplicationFilterChain filterChain = null;
if (request instanceof Request) {
Request req = (Request) request;
if (Globals.IS_SECURITY_ENABLED) {
// Security: Do not recycle
filterChain = new ApplicationFilterChain();
} else {
filterChain = (ApplicationFilterChain) req.getFilterChain();
if (filterChain == null) {
filterChain = new ApplicationFilterChain();
req.setFilterChain(filterChain);
}
}
} else {
// Request dispatcher in use
filterChain = new ApplicationFilterChain();
}
filterChain.setServlet(servlet);
filterChain.setServletSupportsAsync(wrapper.isAsyncSupported());
// Acquire the filter mappings for this Context
StandardContext context = (StandardContext) wrapper.getParent();
FilterMap filterMaps[] = context.findFilterMaps();
// If there are no filter mappings, we are done
if ((filterMaps == null) || (filterMaps.length == 0)) {
return filterChain;
}
// Acquire the information we will need to match filter mappings
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 (FilterMap filterMap : filterMaps) {
if (!matchDispatcher(filterMap, dispatcher)) {
continue;
}
if (!matchFiltersURL(filterMap, requestPath)) {
continue;
}
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
context.findFilterConfig(filterMap.getFilterName());
if (filterConfig == null) {
// FIXME - log configuration problem
continue;
}
filterChain.addFilter(filterConfig);
}
// Add filters that match on servlet name second
for (FilterMap filterMap : filterMaps) {
if (!matchDispatcher(filterMap, dispatcher)) {
continue;
}
if (!matchFiltersServlet(filterMap, servletName)) {
continue;
}
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
context.findFilterConfig(filterMap.getFilterName());
if (filterConfig == null) {
// FIXME - log configuration problem
continue;
}
filterChain.addFilter(filterConfig);
}
// Return the completed filter chain
return filterChain;
}- 通过 new 关键字创建 ApplicationFilterChain
- 获取 Context 中所有的 Filter 实例，并通过路径和 servlet name 筛选出匹配当前 Servlet 的 Filter 实例添加到 ApplicationFilterChain 中
创建成功后调用 filterChain.doFilter() 方法触发过滤器链。
java
@Override
public void doFilter(ServletRequest request, ServletResponse response)
throws IOException, ServletException {
if( Globals.IS_SECURITY_ENABLED ) {
final ServletRequest req = request;
final ServletResponse res = response;
try {
java.security.AccessController.doPrivileged(
new java.security.PrivilegedExceptionAction<Void>() {
@Override
public Void run()
throws ServletException, IOException {
internalDoFilter(req,res);
return null;
}
}
);
} catch( PrivilegedActionException pe) {
Exception e = pe.getException();
if (e instanceof ServletException) {
throw (ServletException) e;
} else if (e instanceof IOException) {
throw (IOException) e;
} else if (e instanceof RuntimeException) {
throw (RuntimeException) e;
} else {
throw new ServletException(e.getMessage(), e);
}
}
} else {
internalDoFilter(request,response);
}
}
private void internalDoFilter(ServletRequest request,
ServletResponse response)
throws IOException, ServletException {
// Call the next filter if there is one
if (pos < n) {
ApplicationFilterConfig filterConfig = filters[pos++];
try {
Filter filter = filterConfig.getFilter();
if (request.isAsyncSupported() && "false".equalsIgnoreCase(
filterConfig.getFilterDef().getAsyncSupported())) {
request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);
}
if( Globals.IS_SECURITY_ENABLED ) {
final ServletRequest req = request;
final ServletResponse res = response;
Principal principal =
((HttpServletRequest) req).getUserPrincipal();
Object[] args = new Object[]{req, res, this};
SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal);
} else {
filter.doFilter(request, response, this);
}
} catch (IOException | ServletException | RuntimeException e) {
throw e;
} catch (Throwable e) {
e = ExceptionUtils.unwrapInvocationTargetException(e);
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("filterChain.filter"), e);
}
return;
}
// We fell off the end of the chain -- call the servlet instance
try {
if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
lastServicedRequest.set(request);
lastServicedResponse.set(response);
}
if (request.isAsyncSupported() && !servletSupportsAsync) {
request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,
Boolean.FALSE);
}
// Use potentially wrapped request from this point
if ((request instanceof HttpServletRequest) &&
(response instanceof HttpServletResponse) &&
Globals.IS_SECURITY_ENABLED ) {
final ServletRequest req = request;
final ServletResponse res = response;
Principal principal =
((HttpServletRequest) req).getUserPrincipal();
Object[] args = new Object[]{req, res};
SecurityUtil.doAsPrivilege("service",
servlet,
classTypeUsedInService,
args,
principal);
} else {
servlet.service(request, response);
}
} catch (IOException | ServletException | RuntimeException e) {
throw e;
} catch (Throwable e) {
e = ExceptionUtils.unwrapInvocationTargetException(e);
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("filterChain.servlet"), e);
} finally {
if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
lastServicedRequest.set(null);
lastServicedResponse.set(null);
}
}
}ApplicationFilterChain 中有一个 pos 变量来记录过滤器链执行位置，执行每次从 Filter 数组 filters 中获取 Filter 后 pos 就加一。等到 Filter 被调用完之后会执行 servlet.service(request, response);。由此可见 Filter 是在 Servlet init 方法执行之后，service 方法执行之前执行的。