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[Java教程]Tomcat源码分析——请求处理准备


前言

  谈起Tomcat的诞生,最早可以追溯到1995年。近20年来,Tomcat始终是使用最广泛的web服务器,由于其使用Java语言开发,所以广为Java程序员所熟悉。很多人早期的J2EE项目,由程序员自己实现jsp页面或者servlet接受请求,后来借助struts1、struts2、spring等中间件后,实际也是利用filter或者servlet处理请求,大家肯定要问了,这些servlet处理的请求来自哪里?Tomcat作为web服务器是怎样将HTTP请求交给servlet的呢?

  本文就Tomcat对HTTP的请求处理细节进行分析。

  提示:阅读本文前,请确保首先理解了《Tomcat源码分析——生命周期管理》中的内容。

Connector的初始化

  根据《Tomcat源码分析——生命周期管理》一文的内容,我们知道Tomcat中有很多容器,包括Server、Service、Connector等。其中Connector正是与HTTP请求处理相关的容器。Service是Server的子容器,而Connector又是Service的子容器。那么这三个容器的初始化顺序为:Server->Service->Connector。Connector的实现分为以下几种:

  • Http Connector:基于HTTP协议,负责建立HTTP连接。它又分为BIO Http Connector与NIO Http Connector两种,后者提供非阻塞IO与长连接Comet支持。
  • AJP Connector:基于AJP协议,AJP是专门设计用于Tomcat与HTTP服务器通信定制的协议,能提供较高的通信速度和效率。如与Apache服务器集成时,采用这个协议。
  • APR HTTP Connector:用C实现,通过JNI调用的。主要提升对静态资源(如HTML、图片、CSS、JS等)的访问性能。现在这个库已独立出来可用在任何项目中。由于APR性能较前两类有很大提升,所以目前是Tomcat的默认Connector。

现在我们直接来看Connector的initInternal方法吧,见代码清单1。

代码清单1

  @Override  protected void initInternal() throws LifecycleException {    super.initInternal();        // Initialize adapter    adapter = new CoyoteAdapter(this);    protocolHandler.setAdapter(adapter);    IntrospectionUtils.setProperty(protocolHandler, "jkHome",                    System.getProperty("catalina.base"));    onameProtocolHandler = register(protocolHandler,        createObjectNameKeyProperties("ProtocolHandler"));        mapperListener.setDomain(getDomain());    onameMapper = register(mapperListener,        createObjectNameKeyProperties("Mapper"));  }

 

代码清单1说明了Connector的初始化步骤如下:

步骤一 构造网络协议处理的CoyoteAdapter

  代码清单1构造了CoyoteAdapter对象,并且将其设置为ProtocolHandler的Adapter。ProtocolHandler是做什么的呢?Tomcat处理HTTP请求,需要有一个ServerSocket监听网络端口来完成任务。接口ProtocolHandler被设计成控制网络端口监听组件运行,负责组件的生命周期控制,这个接口实际并没有定义网络端口监听功能的规范,而是用于负责维护组件的生命周期。从ProtocolHandler的名字来看,它应该是网络协议的处理者,但它实际不负责这个功能,而是将其交给org.apache.coyote.Adapter来完成,这么设计估计是为了方便维护和拓展新功能。Http11Protocol是ProtocolHandler接口的一个实现(是Connector的默认处理协议),被设计用来处理HTTP1.1网络协议的请求,通过该类可以完成在某个网络端口上面的监听,同时以HTTP1.1的协议来解析请求内容,然后将请求传递到Connector所寄居的Container容器pipeline流水工作线上处理。此处的ProtocolHandler是何时生成的呢?还记得《TOMCAT源码分析——SERVER.》一文中的Digester和Rule吗?Digester在解析到<Connector>标签的时候,会执行startElement方法,startElement中会调用Rule的begin(String namespace, String name, Attributes attributes)方法,Connector对应的Rule包括ConnectorCreateRule,的begin方法的实现见代码清单2。

代码清单2

 

  @Override  public void begin(String namespace, String name, Attributes attributes)      throws Exception {    Service svc = (Service)digester.peek();    Executor ex = null;    if ( attributes.getValue("executor")!=null ) {      ex = svc.getExecutor(attributes.getValue("executor"));    }    Connector con = new Connector(attributes.getValue("protocol"));    if ( ex != null ) _setExecutor(con,ex);        digester.push(con);  }

 

代码清单2中调用了Connector的构造器,传递的参数为属性protocol。我们知道server.

  <Connector port="8080" protocol="HTTP/1.1"        connectionTimeout="20000"        redirectPort="8443" />  <!-- Define an AJP 1.3 Connector on port 8009 -->  <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />

我们看看Connector的构造器实现,见代码清单3。

代码清单3

  public Connector(String protocol) {    setProtocol(protocol);    // Instantiate protocol handler    try {      Class<?> clazz = Class.forName(protocolHandlerClassName);      this.protocolHandler = (ProtocolHandler) clazz.newInstance();    } catch (Exception e) {      log.error        (sm.getString         ("coyoteConnector.protocolHandlerInstantiationFailed", e));    }  }

setProtocol方法(见代码清单4)根据protocol参数的不同,调用setProtocolHandlerClassName方法(见代码清单5)设置protocolHandlerClassName属性。以HTTP/1.1为例,由于默认情况下Apr不可用,所以protocolHandlerClassName会被设置为org.apache.coyote.http11.Http11Protocol,那么反射生成的protocolHandler就是Http11Protocol实例。Tomcat默认还会配置协议是AJP/1.3的Connector,那么此Connector的protocolHandler就是org.apache.coyote.ajp.AjpProtocol。

 代码清单4

  /**   * Set the Coyote protocol which will be used by the connector.   *   * @param protocol The Coyote protocol name   */  public void setProtocol(String protocol) {    if (AprLifecycleListener.isAprAvailable()) {      if ("HTTP/1.1".equals(protocol)) {        setProtocolHandlerClassName          ("org.apache.coyote.http11.Http11AprProtocol");      } else if ("AJP/1.3".equals(protocol)) {        setProtocolHandlerClassName          ("org.apache.coyote.ajp.AjpAprProtocol");      } else if (protocol != null) {        setProtocolHandlerClassName(protocol);      } else {        setProtocolHandlerClassName          ("org.apache.coyote.http11.Http11AprProtocol");      }    } else {      if ("HTTP/1.1".equals(protocol)) {        setProtocolHandlerClassName          ("org.apache.coyote.http11.Http11Protocol");      } else if ("AJP/1.3".equals(protocol)) {        setProtocolHandlerClassName          ("org.apache.coyote.ajp.AjpProtocol");      } else if (protocol != null) {        setProtocolHandlerClassName(protocol);      }    }  }

代码清单5

  public void setProtocolHandlerClassName(String protocolHandlerClassName) {    this.protocolHandlerClassName = protocolHandlerClassName;  }

 

除此之外,ProtocolHandler还有其它实现,如图1所示。

 

图1  ProtocolHandler类继承体系

图1中有关ProtocolHandler的实现类都在org.apache.coyote包中 。前面所说的BIO Http Connector实际就是Http11Protocol,NIO Http Connector实际就是Http11NioProtocol,AJP Connector包括AjpProtocol和AjpAprProtocol,APR HTTP Connector包括AjpAprProtocol、Http11AprProtocol,此外还有一个MemoryProtocolHandler(这个是做什么的,目前没搞清楚,有知道的同学告诉我下啊!)。

步骤二 将ProtocolHandler、MapperListener注册到JMX

  BIO Http Connector的ProtocolHandler(即Http11Protocol)的JMX注册名为Catalina:type=ProtocolHandler,port=8080。BIO Http Connector的MapperListener的注册名为Catalina:type=Mapper,port=8080。AJP Connector的ProtocolHandler(即AjpProtocol)的JMX注册名为Catalina:type=ProtocolHandler,port=8009。AJP Connector的MapperListener的注册名为Catalina:type=Mapper,port=8009。有关Tomcat中JMX注册的内容,请阅读《TOMCAT源码分析——生命周期管理》一文。

Connector的启动

  根据《Tomcat源码分析——生命周期管理》一文的内容,我们知道Tomcat中有很多容器。ProtocolHandler的初始化稍微有些特殊,Server、Service、Connector这三个容器的初始化顺序为:Server->Service->Connector。值得注意的是,ProtocolHandler作为Connector的子容器,其初始化过程并不是由Connector的initInternal方法调用的,而是与启动过程一道被Connector的startInternal方法所调用。由于本文的目的是分析请求,所以直接从Connector的initInternal方法(见代码清单6)开始。

代码清单6

  /**   * Begin processing requests via this Connector.   *   * @exception LifecycleException if a fatal startup error occurs   */  @Override  protected void startInternal() throws LifecycleException {    setState(LifecycleState.STARTING);    // Protocol handlers do not follow Lifecycle conventions.    // protocolHandler.init() needs to wait until the connector.start()    try {      protocolHandler.init();    } catch (Exception e) {      throw new LifecycleException        (sm.getString         ("coyoteConnector.protocolHandlerInitializationFailed", e));    }    try {      protocolHandler.start();    } catch (Exception e) {      String errPrefix = "";      if(this.service != null) {        errPrefix += "service.getName(): \"" + this.service.getName() + "\"; ";      }      throw new LifecycleException        (errPrefix + " " + sm.getString         ("coyoteConnector.protocolHandlerStartFailed", e));    }    // MapperListener doesn't follow Lifecycle conventions either    mapperListener.init();  }

代码清单6说明了Connector的initInternal方法的执行顺序如下:

  1. 将Connector容器的状态更改为启动中(LifecycleState.STARTING);
  2. 初始化ProtocolHandler;
  3. 启动ProtocolHandler;
  4. 初始化MapperListener。

初始化ProtocolHandler

  简单起见,我们以Http11Protocol为例剖析ProtocolHandler的init方法,其实现见代码清单7。

代码清单7

  @Override  public void init() throws Exception {    ((JIoEndpoint)endpoint).setName(getName());    ((JIoEndpoint)endpoint).setHandler(cHandler);    // Verify the validity of the configured socket factory    try {      if (isSSLEnabled()) {        sslImplementation =          SSLImplementation.getInstance(sslImplementationName);        socketFactory = sslImplementation.getServerSocketFactory();        ((JIoEndpoint)endpoint).setServerSocketFactory(socketFactory);      } else if (socketFactoryName != null) {        socketFactory = (ServerSocketFactory) Class.forName(socketFactoryName).newInstance();        ((JIoEndpoint)endpoint).setServerSocketFactory(socketFactory);      }    } catch (Exception ex) {      log.error(sm.getString("http11protocol.socketfactory.initerror"),           ex);      throw ex;    }    if (socketFactory!=null) {      Iterator<String> attE = attributes.keySet().iterator();      while( attE.hasNext() ) {        String key = attE.next();        Object v=attributes.get(key);        socketFactory.setAttribute(key, v);      }    }        try {      endpoint.init();    } catch (Exception ex) {      log.error(sm.getString("http11protocol.endpoint.initerror"), ex);      throw ex;    }    if (log.isInfoEnabled())      log.info(sm.getString("http11protocol.init", getName()));  }

从代码清单7看到,Http11Protocol的初始化步骤如下:

步骤一 设置JIoEndpoint的名称

  JIoEndpoint的名称默认为http-8080,这里的JIoEndpoint是在调用Http11Protocol的构造器时创建的,Http11Protocol的构造器中还设置了socket的延迟关闭选项soLingerOn、socket的延时关闭秒数soLingerTime、socket连接超时时间soTimeout、提高socket性能的tcpNoDelay等选项,见代码清单8。

代码清单8

  public Http11Protocol() {    endpoint = new JIoEndpoint();    setSoLinger(Constants.DEFAULT_CONNECTION_LINGER);    setSoTimeout(Constants.DEFAULT_CONNECTION_TIMEOUT);    //setServerSoTimeout(Constants.DEFAULT_SERVER_SOCKET_TIMEOUT);    setTcpNoDelay(Constants.DEFAULT_TCP_NO_DELAY);      }

步骤二 设置JIoEndpoint的Handler

  JIoEndpoint的handler被设置为cHandler,此cHandler的定义如下:

  protected Http11ConnectionHandler cHandler = new Http11ConnectionHandler(this);

步骤三 配置ServerSocketFactory

从代码清单7看到,生成ServerSocketFactory有三种方式:
  • 如果在server.ServerSocketFactory;

  • 如果Http11Protocol指定了socketFactoryName,则使用socketFactoryName反射生成ServerSocketFactory实例;
  • 如果不满足以上2个条件,那么JIoEndpoint的init方法(见代码清单9)将创建ServerSocketFactory。当SSLEnabled="true"时,JIoEndpoint的init方法还会给ServerSocketFactory设置一些SSL相关的属性。最后使用此ServerSocketFactory创建serverSocket。此外,acceptorThreadCount属性用于指定接受连接的线程数,可以通过给Connector设置acceptorThreadCount属性进行调整,默认值为1。

代码清单9

  @Override  public void init()    throws Exception {    if (initialized)      return;        // Initialize thread count defaults for acceptor    if (acceptorThreadCount == 0) {      acceptorThreadCount = 1;    }    if (serverSocketFactory == null) {      serverSocketFactory = ServerSocketFactory.getDefault();    }    if (isSSLEnabled()) {      serverSocketFactory.setAttribute(SSL_ATTR_ALGORITHM,          getAlgorithm());      serverSocketFactory.setAttribute(SSL_ATTR_CLIENT_AUTH,          getClientAuth());      serverSocketFactory.setAttribute(SSL_ATTR_KEYSTORE_FILE,          getKeystoreFile());      serverSocketFactory.setAttribute(SSL_ATTR_KEYSTORE_PASS,          getKeystorePass());      serverSocketFactory.setAttribute(SSL_ATTR_KEYSTORE_TYPE,          getKeystoreType());      serverSocketFactory.setAttribute(SSL_ATTR_KEYSTORE_PROVIDER,          getKeystoreProvider());      serverSocketFactory.setAttribute(SSL_ATTR_SSL_PROTOCOL,          getSslProtocol());      serverSocketFactory.setAttribute(SSL_ATTR_CIPHERS,          getCiphers());      serverSocketFactory.setAttribute(SSL_ATTR_KEY_ALIAS,          getKeyAlias());      serverSocketFactory.setAttribute(SSL_ATTR_KEY_PASS,          getKeyPass());      serverSocketFactory.setAttribute(SSL_ATTR_TRUSTSTORE_FILE,          getTruststoreFile());      serverSocketFactory.setAttribute(SSL_ATTR_TRUSTSTORE_PASS,          getTruststorePass());      serverSocketFactory.setAttribute(SSL_ATTR_TRUSTSTORE_TYPE,          getTruststoreType());      serverSocketFactory.setAttribute(SSL_ATTR_TRUSTSTORE_PROVIDER,          getTruststoreProvider());      serverSocketFactory.setAttribute(SSL_ATTR_TRUSTSTORE_ALGORITHM,          getTruststoreAlgorithm());      serverSocketFactory.setAttribute(SSL_ATTR_CRL_FILE,          getCrlFile());      serverSocketFactory.setAttribute(SSL_ATTR_TRUST_MAX_CERT_LENGTH,          getTrustMaxCertLength());      serverSocketFactory.setAttribute(SSL_ATTR_SESSION_CACHE_SIZE,          getSessionCacheSize());      serverSocketFactory.setAttribute(SSL_ATTR_SESSION_TIMEOUT,          getSessionTimeout());      serverSocketFactory.setAttribute(SSL_ATTR_ALLOW_UNSAFE_RENEG,          getAllowUnsafeLegacyRenegotiation());    }    if (serverSocket == null) {      try {        if (getAddress() == null) {          serverSocket = serverSocketFactory.createSocket(getPort(), getBacklog());        } else {          serverSocket = serverSocketFactory.createSocket(getPort(), getBacklog(), getAddress());        }      } catch (BindException orig) {        String msg;        if (getAddress() == null)          msg = orig.getMessage() + " <null>:" + getPort();        else          msg = orig.getMessage() + " " +              getAddress().toString() + ":" + getPort();        BindException be = new BindException(msg);        be.initCause(orig);        throw be;      }    }    //if( serverTimeout >= 0 )    //  serverSocket.setSoTimeout( serverTimeout );        initialized = true;      }

启动ProtocolHandler

  我们继续以Http11Protocol为例,剖析ProtocolHandler的start方法,其实现见代码清单10。

代码清单10

  @Override  public void start() throws Exception {    if (this.domain != null) {      try {        tpOname = new ObjectName          (domain + ":" + "type=ThreadPool,name=" + getName());        Registry.getRegistry(null, null)          .registerComponent(endpoint, tpOname, null );      } catch (Exception e) {        log.error("Can't register endpoint");      }      rgOname=new ObjectName        (domain + ":type=GlobalRequestProcessor,name=" + getName());      Registry.getRegistry(null, null).registerComponent        ( cHandler.global, rgOname, null );    }    try {      endpoint.start();    } catch (Exception ex) {      log.error(sm.getString("http11protocol.endpoint.starterror"), ex);      throw ex;    }    if (log.isInfoEnabled())      log.info(sm.getString("http11protocol.start", getName()));  }

 从代码清单10可以知道JIoEndpoint以Catalina:type=ThreadPool,name=http-8080注册到JMX,cHandler.global(Http11ConnectionHandler的对象属性,类型为RequestGroupInfo)以Catalina:type=GlobalRequestProcessor,name=http-8080注册到JMX。最后调用JIoEndpoint的start方法(见代码清单11)接受请求的创建线程池并创建一定数量的接收请求线程。

代码清单11

  @Override  public void start() throws Exception {    // Initialize socket if not done before    if (!initialized) {      init();    }    if (!running) {      running = true;      paused = false;      // Create worker collection      if (getExecutor() == null) {        createExecutor();      }      // Start acceptor threads      for (int i = 0; i < acceptorThreadCount; i++) {        Thread acceptorThread = new Thread(new Acceptor(), getName() + "-Acceptor-" + i);        acceptorThread.setPriority(threadPriority);        acceptorThread.setDaemon(getDaemon());        acceptorThread.start();      }    }  }

从代码清单11看出JIoEndpoint的start方法的执行步骤如下:

步骤一 对JIoEndpoint做初始化检查

  这一步实际就是判断是否已经初始化(即initialized是否为true),如果没有初始化则需要调用JIoEndpoint的init方法进行初始化。

步骤二 创建线程池与任务队列

  如果JIoEndpoint尚未处于运行中(即running等于true),才会创建线程池和任务队列。如果尚未创建线程池(即调用getExecutor方法等于null),则需要调用createExecutor方法(见代码清单12)创建线程池和任务队列TaskQueue。

代码清单12

  public void createExecutor() {    internalExecutor = true;    TaskQueue taskqueue = new TaskQueue();    TaskThreadFactory tf = new TaskThreadFactory(getName() + "-exec-", daemon, getThreadPriority());    executor = new ThreadPoolExecutor(getMinSpareThreads(), getMaxThreads(), 60, TimeUnit.SECONDS,taskqueue, tf);    taskqueue.setParent( (ThreadPoolExecutor) executor);  }

  

步骤三 创建接收请线程

  如果JIoEndpoint尚未处于运行中(即running等于true),才会创建接收请求线程。从代码清单11可以看出接收请求线程的数量主要由acceptorThreadCount控制,代码清单9已经告诉我们acceptorThreadCount的默认值为1,但是我们可以通过给Connector增加acceptorThreadCount属性来修改接收请求线程的数量。这些接收请求线程的主要工作由Acceptor完成,Acceptor的实质是一个Runnable,见代码清单13。

代码清单13

  /**   * Server socket acceptor thread.   */  protected class Acceptor implements Runnable {    /**     * 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 (running) {        // Loop if endpoint is paused        while (paused) {          try {            Thread.sleep(1000);          } catch (InterruptedException e) {            // Ignore          }        }        // Accept the next incoming connection from the server socket        try {          Socket socket = serverSocketFactory.acceptSocket(serverSocket);          serverSocketFactory.initSocket(socket);          // Hand this socket off to an appropriate processor          if (!processSocket(socket)) {            // Close socket right away            try {              socket.close();            } catch (IOException e) {              // Ignore            }          }        }catch ( IOException x ) {          if ( running ) log.error(sm.getString("endpoint.accept.fail"), x);        } catch (Throwable t) {          log.error(sm.getString("endpoint.accept.fail"), t);        }        // The processor will recycle itself when it finishes      }    }  }

 

初始化MapperListener

  MapperListener的init方法用于初始化,见代码清单14。

代码清单14

 

  /**   * Initialize associated mapper.   */  public void init() {    // Find any components that have already been initialized since the    // MBean listener won't be notified as those components will have    // already registered their MBeans    findDefaultHost();        Engine engine = (Engine) connector.getService().getContainer();    engine.addContainerListener(this);        Container[] conHosts = engine.findChildren();    for (Container conHost : conHosts) {      Host host = (Host) conHost;      if (!LifecycleState.NEW.equals(host.getState())) {        host.addLifecycleListener(this);        // Registering the host will register the context and wrappers        registerHost(host);      }    }  }

 

从代码清单14看到MapperListener的初始化步骤如下:

步骤一 查找默认Host

  StandardService的子容器包括:StandardEngine、Connector和Executor。MapperListener本身会持有Connector,所以可以通过各个容器的父子关系,找到Connector的同级容器StandardEngine。StandardHost是StandardEngine的子容器,Engine和Host的默认配置如下:

  <Engine name="Catalina" defaultHost="localhost">   <Realm className="org.apache.catalina.realm.UserDatabaseRealm"       resourceName="UserDatabase"/>   <Host name="localhost" appBase="webapps"      unpackWARs="true" autoDeploy="true">    <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"         prefix="localhost_access_log." suffix=".txt"        pattern="%h %l %u %t &quot;%r&quot; %s %b" resolveHosts="false"/>   </Host>  </Engine>

findDefaultHost方法(见代码清单15)可以获取上面配置中的默认Host,Engine元素的defaultHost属性值必须要与配置的某个Host元素的name属性值相同。如果defaultHost的属性值配置无误,则会添加为MapperListener的Mapper对象属性的defaultHostName。

代码清单15

  private void findDefaultHost() {    Engine engine = (Engine) connector.getService().getContainer();    String defaultHost = engine.getDefaultHost();    boolean found = false;    if (defaultHost != null && defaultHost.length() >0) {      Container[] containers = engine.findChildren();            for (Container container : containers) {        Host host = (Host) container;        if (defaultHost.equalsIgnoreCase(host.getName())) {          found = true;          break;        }                String[] aliases = host.findAliases();        for (String alias : aliases) {          if (defaultHost.equalsIgnoreCase(alias)) {            found = true;            break;          }        }      }    }    if(found) {      mapper.setDefaultHostName(defaultHost);    } else {      log.warn(sm.getString("mapperListener.unknownDefaultHost",          defaultHost));    }  }

 

 步骤二 将Host及其子容器Context,Context的子容器Wrapper注册到MapperListener的Mapper对象

  Mapper的数据结构,见代码清单16。

                          代码清单16
  /**   * Array containing the virtual hosts definitions.   */  protected Host[] hosts = new Host[0];  /**   * Default host name.   */  protected String defaultHostName = null;  /**   * Context associated with this wrapper, used for wrapper mapping.   */  protected Context context = new Context();  protected static abstract class MapElement {    public String name = null;    public Object object = null;  }  protected static final class Host    extends MapElement {    public ContextList contextList = null;  }  protected static final class ContextList {    public Context[] contexts = new Context[0];    public int nesting = 0;  }  protected static final class Context    extends MapElement {    public String path = null;    public String[] welcomeResources = new String[0];    public javax.naming.Context resources = null;    public Wrapper defaultWrapper = null;    public Wrapper[] exactWrappers = new Wrapper[0];    public Wrapper[] wildcardWrappers = new Wrapper[0];    public Wrapper[] extensionWrappers = new Wrapper[0];    public int nesting = 0;  }  protected static class Wrapper    extends MapElement {    public String path = null;    public boolean jspWildCard = false;  }

根据代码清单16,我们知道Mapper中维护着一个Host数组,每个Host中有一个ContextList,这个ContextList中维护着一个Context数组。每个Context维护着一个defaultWrapper,三个Wrapper数组(exactWrappers、wildcardWrappers、extensionWrappers)。下面对Host、Context及Wrapper进行功能上的介绍:

  • Host:代表一个虚拟主机,各Host的name不能相同,appBase代表各虚拟主机的应用发布位置;
  • Context:代表一个应用,Context可以根据应用的/WEB-INF/web.
  • Wrapper: 代表一个Servlet或者jsp,它负责管理一个 Servlet,包括的 Servlet 的装载、初始化、执行以及资源回收。

 以我本地为例,注册到Mapper中的Host及其子容器如图2所示。

图2  注册到Mapper中的Host及其Context子容器

 图2说明Host内一共5个Context,由于我的Tomcat是从svn拉下来的,所以webapps目录下的.svn文件夹也是一个Context,除了这个天外来客,我将其它与请求有关的容器整理后用图3来展示。

图3  我本地的Host、Context及Wrapper

  至此,Tomcat中为请求处理的准备工作已经完成。有关请求的处理过程将在之后的博文中献上。