How Tomcat Works（五）

lujiguo115

　　本文接下来介绍tomcat的默认连接器，Tomcat中的默认连接器必须满足以下要求：

• 　　实现org.apache.catalina.Connector接口
  
  
• 　　负责创建实现org.apache.catalina.Request接口的Request对象
  
  
• 　　负责创建实现org.apache.catalina.Response接口的Response对象
  
  

　　org.apache.catalina.Connector接口最重要的方法是getContainer() 、setContainer()、creatRequest()、 creatResponse()，setContainer()方法用于设置相关联的servlet容器，getContainer()方法获取相关连的servlet容器，creatRequest()方法为http请求创建request对象，creatResponse()方法创建response对象
　　下面来分析HttpConnector类实现，HttpConnector类同时实现了org.apache.catalina.Connector接口org.apache.catalina.Lifecycle接口（用于生命周期管理）、java.lang.Runnable接口（多线程接口）
　　在HttpConnector对象的初始化方法initialize()里面，调用私有方法open()，创建ServerSocket实例



private ServerSocket open()
throws IOException, KeyStoreException, NoSuchAlgorithmException,
CertificateException, UnrecoverableKeyException,
KeyManagementException
{
// Acquire the server socket factory for this Connector
ServerSocketFactory factory = getFactory();
// If no address is specified, open a connection on all addresses
if (address == null) {
log(sm.getString("httpConnector.allAddresses"));
try {
return (factory.createSocket(port, acceptCount));
} catch (BindException be) {
throw new BindException(be.getMessage() + ":" + port);
}
}
// Open a server socket on the specified address
try {
InetAddress is = InetAddress.getByName(address);
log(sm.getString("httpConnector.anAddress", address));
try {
return (factory.createSocket(port, acceptCount, is));
} catch (BindException be) {
throw new BindException(be.getMessage() + ":" + address +
":" + port);
}
} catch (Exception e) {
log(sm.getString("httpConnector.noAddress", address));
try {
return (factory.createSocket(port, acceptCount));
} catch (BindException be) {
throw new BindException(be.getMessage() + ":" + port);
}
}
}
　　上面的ServerSocketFactory factory = getFactory()显然是创建ServerSocket实例的工厂，方法如下



/**
* Return the server socket factory used by this Container.
*/
public ServerSocketFactory getFactory() {
if (this.factory == null) {
synchronized (this) {
this.factory = new DefaultServerSocketFactory();
}
}
return (this.factory);
}
　　工厂类DefaultServerSocketFactory实现了ServerSocketFactory接口



public final class DefaultServerSocketFactory implements ServerSocketFactory {

public ServerSocket createSocket (int port)
throws IOException, KeyStoreException, NoSuchAlgorithmException,
CertificateException, UnrecoverableKeyException,
KeyManagementException {
return (new ServerSocket(port));
}

public ServerSocket createSocket (int port, int backlog)
throws IOException, KeyStoreException, NoSuchAlgorithmException,
CertificateException, UnrecoverableKeyException,
KeyManagementException {
return (new ServerSocket(port, backlog));
}

public ServerSocket createSocket (int port, int backlog,
InetAddress ifAddress)
throws IOException, KeyStoreException, NoSuchAlgorithmException,
CertificateException, UnrecoverableKeyException,
KeyManagementException {
return (new ServerSocket(port, backlog, ifAddress));
}
}
　　下面接着分析用于生命周期的start()方法



/**
* Begin processing requests via this Connector.
*
* @exception LifecycleException if a fatal startup error occurs
*/
public void start() throws LifecycleException {
// Validate and update our current state
if (started)
throw new LifecycleException
(sm.getString("httpConnector.alreadyStarted"));
threadName = "HttpConnector[" + port + "]";
lifecycle.fireLifecycleEvent(START_EVENT, null);
started = true;
// Start our background thread
        threadStart();
// Create the specified minimum number of processors
while (curProcessors < minProcessors) {
if ((maxProcessors > 0) && (curProcessors >= maxProcessors))
break;
HttpProcessor processor = newProcessor();
recycle(processor);
}
}
　　首先是启动HttpConnector连接器线程，然后是初始化最少数量的HttpProcessor处理器入栈



/**
* Start the background processing thread.
*/
private void threadStart() {
log(sm.getString("httpConnector.starting"));
thread = new Thread(this, threadName);
thread.setDaemon(true);
thread.start();
}
　　由于HttpConnector连接器实现了java.lang.Runnable接口，我们分析它的run()方法实现



/**
* The background thread that listens for incoming TCP/IP connections and
* hands them off to an appropriate processor.
*/
public void run() {
// Loop until we receive a shutdown command
while (!stopped) {
// Accept the next incoming connection from the server socket
Socket socket = null;
try {
//                if (debug >= 3)
//                    log("run: Waiting on serverSocket.accept()");
socket = serverSocket.accept();
//                if (debug >= 3)
//                    log("run: Returned from serverSocket.accept()");
if (connectionTimeout > 0)
socket.setSoTimeout(connectionTimeout);
socket.setTcpNoDelay(tcpNoDelay);
} catch (AccessControlException ace) {
log("socket accept security exception", ace);
continue;
} catch (IOException e) {
//                if (debug >= 3)
//                    log("run: Accept returned IOException", e);
try {
// If reopening fails, exit
synchronized (threadSync) {
if (started && !stopped)
log("accept error: ", e);
if (!stopped) {
//                    if (debug >= 3)
//                        log("run: Closing server socket");
                            serverSocket.close();
//                        if (debug >= 3)
//                            log("run: Reopening server socket");
serverSocket = open();
}
}
//                    if (debug >= 3)
//                        log("run: IOException processing completed");
} catch (IOException ioe) {
log("socket reopen, io problem: ", ioe);
break;
} catch (KeyStoreException kse) {
log("socket reopen, keystore problem: ", kse);
break;
} catch (NoSuchAlgorithmException nsae) {
log("socket reopen, keystore algorithm problem: ", nsae);
break;
} catch (CertificateException ce) {
log("socket reopen, certificate problem: ", ce);
break;
} catch (UnrecoverableKeyException uke) {
log("socket reopen, unrecoverable key: ", uke);
break;
} catch (KeyManagementException kme) {
log("socket reopen, key management problem: ", kme);
break;
}
continue;
}
// Hand this socket off to an appropriate processor
HttpProcessor processor = createProcessor();
if (processor == null) {
try {
log(sm.getString("httpConnector.noProcessor"));
socket.close();
} catch (IOException e) {
;
}
continue;
}
//            if (debug >= 3)
//                log("run: Assigning socket to processor " + processor);
            processor.assign(socket);
// The processor will recycle itself when it finishes

}
// Notify the threadStop() method that we have shut ourselves down
//        if (debug >= 3)
//            log("run: Notifying threadStop() that we have shut down");
synchronized (threadSync) {
threadSync.notifyAll();
}
}
　　上面方法中，监听客户端的http请求，当监听到http请求时，获取Socket实例，然后委派给HttpProcessor对象进行处理（处理器线程吧），最后是如果收到停止连接器线程命令， 则事件通知可以停止线程了
　　在上面我们还没有来得及分析HttpProcessor对象的初始化相关，所以要重新回到start()方法（源码分析有时要跟踪方法中对多个其他方法的调用，深度优先则顾此失彼，难以兼顾；而广度优先则不便纵向深入）



// Create the specified minimum number of processors
while (curProcessors < minProcessors) {
if ((maxProcessors > 0) && (curProcessors >= maxProcessors))
break;
HttpProcessor processor = newProcessor();
recycle(processor);
}
　　这里是创建最少数量的HttpProcessor处理器并入栈，我们先分析newProcessor()方法的实现



/**
* Create and return a new processor suitable for processing HTTP
* requests and returning the corresponding responses.
*/
private HttpProcessor newProcessor() {
//        if (debug >= 2)
//            log("newProcessor: Creating new processor");
HttpProcessor processor = new HttpProcessor(this, curProcessors++);
if (processor instanceof Lifecycle) {
try {
((Lifecycle) processor).start();
} catch (LifecycleException e) {
log("newProcessor", e);
return (null);
}
}
created.addElement(processor);
return (processor);
}
　　我们可以看到，这里主要是实例化HttpProcessor对象，传入HttpConnector实例本身（里面要用到HttpConnector对象的创建Request对象方法和创建Response对象方法），然后向上转型为Lifecycle接口类型，并调用它的start()方法，接着Vector created = new Vector()成员变量添加该HttpProcessor对象（Vector实现List接口，内部采用数组实现，其操作方法支持线程同步），最后返回实例



/**
* Recycle the specified Processor so that it can be used again.
*
* @param processor The processor to be recycled
*/
void recycle(HttpProcessor processor) {
//        if (debug >= 2)
//            log("recycle: Recycling processor " + processor);
        processors.push(processor);
}
　　这里将HttpProcessor对象入栈，成员变量Stack processors = new Stack()继承自Vector，是一种先进后出的数据结构
　　我们现在来分析run()方法里面的相关源码，也许更容易理解



/**
* Create (or allocate) and return an available processor for use in
* processing a specific HTTP request, if possible.  If the maximum
* allowed processors have already been created and are in use, return
* <code>null</code> instead.
*/
private HttpProcessor createProcessor() {
synchronized (processors) {
if (processors.size() > 0) {
// if (debug >= 2)
// log("createProcessor: Reusing existing processor");
return ((HttpProcessor) processors.pop());
}
if ((maxProcessors > 0) && (curProcessors < maxProcessors)) {
// if (debug >= 2)
// log("createProcessor: Creating new processor");
return (newProcessor());
} else {
if (maxProcessors < 0) {
// if (debug >= 2)
// log("createProcessor: Creating new processor");
return (newProcessor());
} else {
// if (debug >= 2)
// log("createProcessor: Cannot create new processor");
return (null);
}
}
}
}
　　这里是从Stack processors = new Stack()成员变量里面获取HttpProcessor对象 ，后面的代码不用多加解释了吧，你懂的！
　　后面那段代码是干嘛的



// Notify the threadStop() method that we have shut ourselves down
//        if (debug >= 3)
//            log("run: Notifying threadStop() that we have shut down");
synchronized (threadSync) {
threadSync.notifyAll();
}
　　我们看到threadStop()方法里面的代码，可以看出上面的代码块是用来通知线程停止的



/**
* Stop the background processing thread.
*/
private void threadStop() {
log(sm.getString("httpConnector.stopping"));
stopped = true;
try {
threadSync.wait(5000);
} catch (InterruptedException e) {
;
}
thread = null;
}
　　由于HttpProcessor处理器类的源码分析相对独立，加上篇幅还比较多，因此本文先到这里，下文继续……
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