EndPoint的组件就是属于连接器Connector里面的。它是一个通信的端点，就是负责对外实现TCP/IP协议。EndPoint是个接口，它的具体实现类就是AbstractEndpoint，而AbstractEndpoint具体的实现类就有AprEndpoint、Nio2Endpoint、NioEndpoint。
AprEndpoint：对应的是APR模式，简单理解就是从操作系统级别解决异步IO的问题，大幅度提高服务器的处理和响应性能。但是启用这种模式需要安装一些其他的依赖库。
Nio2Endpoint：利用代码来实现异步IO
NioEndpoint：利用了JAVA的NIO实现了非阻塞IO，Tomcat默认启动是以这个来启动的，而这个也是我们的讲述重点。
在代码NioEndpoint.class中定义的这五个组件。具体这五个组件是干嘛的呢？
LimitLatch：连接控制器，负责控制最大的连接数
Acceptor：负责接收新的连接，然后返回一个Channel对象给Poller
Poller：可以将其看成是NIO中Selector，负责监控Channel的状态
SocketProcessor：可以看成是一个被封装的任务类
Executor：Tomcat自己扩展的线程池，用来执行任务类
组件间的关联关系：
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启动NioEndpoint的Acceptor多线程，默认初始化一个Acceptor：此处与8之前的版本有更新！！！
package org.apache.tomcat.util.net；
public abstract class AbstractEndpoint<S>
/** * Acceptor是接收连接的，我们可以看到Acceptor实现了Runnable接口， * 那么在哪会新开启线程来执行Acceptor的run方法呢？ * 在AbstractEndpoint的startAcceptorThreads方法中。 */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(); }}
@Overrideprotected AbstractEndpoint.Acceptor createAcceptor() { return new Acceptor();}具体类的实现内容：1、执行run方法，启动socket服务；2、关闭socket服务。
/** * The background thread that listens for incoming TCP/IP connections and * hands them off to an appropriate processor. * 重要方法 */protected class Acceptor extends AbstractEndpoint.Acceptor { @Override public void run() { int errorDelay = 0; // Loop until we receive a shutdown command while (running) { // Loop if endpoint is paused while (paused && running) { state = AcceptorState.PAUSED; try { Thread.sleep(50); } catch (InterruptedException e) { // Ignore } } if (!running) { break; } state = AcceptorState.RUNNING; try { //if we have reached max connections, wait （默认是 private int maxConnections = 10000;）
countUpOrAwaitConnection(); SocketChannel socket = null; try { // Accept the next incoming connection from the server // socket socket = serverSock.accept(); } catch (IOException ioe) { // We didn't get a socket countDownConnection(); if (running) { // 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 (running && !paused) { // setSocketOptions() will hand the socket off to // an appropriate processor if successful if (!setSocketOptions(socket)) { closeSocket(socket); } } else { closeSocket(socket); } } catch (Throwable t) { ExceptionUtils.handleThrowable(t); log.error(sm.getString("endpoint.accept.fail"), t); } } state = AcceptorState.ENDED; } private void closeSocket(SocketChannel socket) { countDownConnection(); try { socket.socket().close(); } catch (IOException ioe) { if (log.isDebugEnabled()) { log.debug(sm.getString("endpoint.err.close"), ioe); } } try { socket.close(); } catch (IOException ioe) { if (log.isDebugEnabled()) { log.debug(sm.getString("endpoint.err.close"), ioe); } } }}
package sun.nio.ch;
ServerSocketChannelImpl.class
public SocketChannel accept() throws IOException { synchronized(this.lock) { if (!this.isOpen()) { throw new ClosedChannelException(); } else if (!this.isBound()) { throw new NotYetBoundException(); } else { SocketChannelImpl var2 = null; int var3 = 0; FileDescriptor var4 = new FileDescriptor(); InetSocketAddress[] var5 = new InetSocketAddress[1]; InetSocketAddress var6; try { this.begin(); if (!this.isOpen()) { var6 = null; return var6; } this.thread = NativeThread.current(); do { var3 = this.accept(this.fd, var4, var5); } while(var3 == -3 && this.isOpen()); } finally { this.thread = 0L; this.end(var3 > 0); assert IOStatus.check(var3); } if (var3 < 1) { return null; } else { IOUtil.configureBlocking(var4, true); var6 = var5[0]; var2 = new SocketChannelImpl(this.provider(), var4, var6); SecurityManager var7 = System.getSecurityManager(); if (var7 != null) { try { var7.checkAccept(var6.getAddress().getHostAddress(), var6.getPort()); } catch (SecurityException var13) { var2.close(); throw var13; } } return var2; } } }}
private int accept(FileDescriptor var1, FileDescriptor var2, InetSocketAddress[] var3) throws IOException { return this.accept0(var1, var2, var3);}private native int accept0(FileDescriptor var1, FileDescriptor var2, InetSocketAddress[] var3) throws IOException;
