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介绍：

Tomcat中绑定、监听端口、注册到Poller、事件触发都在EndPoint组件里面处理。

结构图：

Endpoint.png

主要可以分析下NioEndpoint的代码，另外Nio2Endpoint和AprEndpoint用的频率不是很高。
使用了模板模式：AbstractEndpoint是一个抽象类，抽象方法如下：

    public abstract void bind() throws Exception;
    public abstract void unbind() throws Exception;
    public abstract void startInternal() throws Exception;
    public abstract void stopInternal() throws Exception;

流程简介：

NioEndpoint的startInternal方法，用来启动当前组件，创建Acceptor、Poller...

启动组件.png

绑定端口：

    @Override
    public void bind() throws Exception {
        initServerSocket();

        setStopLatch(new CountDownLatch(1));

        // Initialize SSL if needed
        initialiseSsl();

        selectorPool.open(getName());
    }

socket注册到poller，poller里面有selector变量...

        public void register(final NioChannel socket, final NioSocketWrapper socketWrapper) {
            socketWrapper.interestOps(SelectionKey.OP_READ);//this is what OP_REGISTER turns into.
            PollerEvent event = null;
            if (eventCache != null) {
                event = eventCache.pop();
            }
            if (event == null) {
                event = new PollerEvent(socket, OP_REGISTER);
            } else {
                event.reset(socket, OP_REGISTER);
            }
            addEvent(event);
        }

感知事件变化,Poller的run方法：

@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 socketWrapper = (NioSocketWrapper) sk.attachment();
                    // Attachment may be null if another thread has called
                    // cancelledKey()
                    if (socketWrapper == null) {
                        iterator.remove();
                    } else {
                        iterator.remove();
                        processKey(sk, socketWrapper);
                    }
                }

                // Process timeouts
                timeout(keyCount,hasEvents);
            }

            getStopLatch().countDown();
        }

总结：

不积跬步，无以至千里...