tomcat(13)Host和Engine容器

【0】README

0.1）本文部分文字描述转自 “how tomcat works”，旨在学习 “tomcat(13)Host和Engine容器” 的基础知识；

0.2）Host容器：若你想在同一个tomcat部署上运行多个Context 容器的话，就需要使用 Host 容器；它是Context容器的父容器；（干货——若你想在同一个tomcat部署上运行多个Context 容器的话，就需要使用 Host 容器，Host容器表示包含有一个或多个 Context容器的虚拟主机）

0.3）Engine容器：表示Catalina的整个servlet 引擎。如果使用了Engine容器，那么它总是处于容器层级的最顶层；添加到Engine 容器中的子容器通常是 org.apache.catalina.Host的实现。默认情况下，tomcat 会使用 Engine容器的，并且有一个Host容器作为其子容器；（干货——Engine表示Catalina的整个servlet 引擎，并且有一个Host容器作为其子容器）

0.4）本文内容概览

step1）首先介绍Host接口及其相关实现类 StandardHost类， StandardHostMapper 类和 StandardHostValve类；

step2）接下来使用一个应用程序来说明如何使用Host实例作为一个顶层servlet容器；

step3）介绍Engine接口及其相关实现类 StandardEngine 和 StandardEngineValve类，并使用一个app 说明如何使用Engine实例作为顶层 servlet容器；

0.5）for complete source code, please visit https://github.com/pacosonTang/HowTomcatWorks/tree/master/chapter13

【1】Host接口（org.apache.catalina.Host）

1）源码如下

public interface Host extends Container { // org.apache.catalina.Hostpublic static final String ADD_ALIAS_EVENT = "addAlias";    public static final String REMOVE_ALIAS_EVENT = "removeAlias"; public String getAppBase();    public void setAppBase(String appBase);    public boolean getAutoDeploy();   public void setAutoDeploy(boolean autoDeploy);    public void addDefaultContext(DefaultContext defaultContext); public DefaultContext getDefaultContext();     public String getName();    public void setName(String name); public void importDefaultContext(Context context); public void addAlias(String alias); public String[] findAliases();    public Context map(String uri);  // highlight line.public void removeAlias(String alias);
}

对以上代码的分析（Analysis）：Host接口中比较重要的方法是 map()方法，该方法返回一个用来处理引入的http 请求的Context容器的实例；具体实现在 StandardHost类中；

【2】StandardHost类

1）StandardHost的构造函数

public class StandardHost  extends ContainerBase implements Deployer, Host { //org.apache.catalina.core.StandardHostpublic StandardHost() {super();pipeline.setBasic(new StandardHostValve());}

2）调用其start()方法时，会添加两个阀，分别是ErrorReportValve类和ErrorDispatchValve类的实例。start()方法源代码如下：

public synchronized void start() throws LifecycleException {  //org.apache.catalina.core.StandardHost.start().// Set error report valveif ((errorReportValveClass != null)&& (!errorReportValveClass.equals(""))) {try {Valve valve = (Valve) Class.forName(errorReportValveClass).newInstance();addValve(valve); // highlight line.} catch (Throwable t) {log(sm.getString("standardHost.invalidErrorReportValveClass",errorReportValveClass));}}// Set dispatcher valveaddValve(new ErrorDispatcherValve()); // highlight line.super.start(); // highlight line.}
// private String errorReportValveClass =  "org.apache.catalina.valves.ErrorReportValve"; // defined in StandardHost

public synchronized void addValve(Valve valve) { //org.apache.catalina.core.ContainerBase.addValve().pipeline.addValve(valve);fireContainerEvent(ADD_VALVE_EVENT, valve);}

3）每当引入一个http请求时都会调用Host.invoke()方法：由于StandardHost类并没有invoke方法，故调用ContainerBase.invoke()方法，接着调用StandardHost实例的基础阀StandardHostValve.invoke()方法；而StandardHostValve.invoke()方法会调用 StandardHost.map()方法来获取相应的Context实例来处理http 请求。

4）StandardHost.map()方法源代码如下：

 public Context map(String uri) { //org.apache.catalina.core.StandardHost.map().if (debug > 0)log("Mapping request URI '" + uri + "'");if (uri == null)return (null);// Match on the longest possible context path prefixif (debug > 1)log("  Trying the longest context path prefix");Context context = null;String mapuri = uri;while (true) {context = (Context) findChild(mapuri);if (context != null)break;int slash = mapuri.lastIndexOf('/');if (slash < 0)break;mapuri = mapuri.substring(0, slash);}// If no Context matches, select the default Contextif (context == null) {if (debug > 1)log("  Trying the default context");context = (Context) findChild("");}// Complain if no Context has been selectedif (context == null) {log(sm.getString("standardHost.mappingError", uri));return (null);}// Return the mapped Context (if any)if (debug > 0)log(" Mapped to context '" + context.getPath() + "'");return (context);}

Attention）在tomcat4中， ContainerBase类也有map()方法，而 ContainerBase.map()方法会调用 StandardHost.map()方法；（而在tomcat5中，映射器组件已经移除，Context实例是通过request对象来获取的）

【3】StandardHostMapper类（org.apache.catalina.core.StandardHostMapper）

1）在tomcat4中， ContainerBase类（即StandardHost的父类）会调用其 addDefaultMapper() 方法创建一个默认映射器。默认映射器的类型由 mapperClass属性的值决定，ContainerBase.addDefaultMapper()方法的源代码如下：

protected void addDefaultMapper(String mapperClass) { //org.apache.catalina.core.ContainerBase.addDefaultMapper().if (mapperClass == null)return;if (mappers.size() >= 1)return;// Instantiate and add a default Mappertry {Class clazz = Class.forName(mapperClass);Mapper mapper = (Mapper) clazz.newInstance();mapper.setProtocol("http");addMapper(mapper);} catch (Exception e) {log(sm.getString("containerBase.addDefaultMapper", mapperClass),e);}}

对上述代码的分析（Analysis）：

A1）mapperClass的值定义在 StandardHost 类中：

private String mapperClass =  "org.apache.catalina.core.StandardHostMapper"; //defined in org.apache.catalina.core.StandardHost

A2）StandardHost.start()方法：会在方法末尾调用父类的 start()方法（ContainerBase.start()方法），确保默认映射器创建完成；

public synchronized void start() throws LifecycleException { //org.apache.catalina.core.ContainerBase.start().// Validate and update our current component stateif (started)throw new LifecycleException(sm.getString("containerBase.alreadyStarted", logName()));// Notify our interested LifecycleListenerslifecycle.fireLifecycleEvent(BEFORE_START_EVENT, null);addDefaultMapper(this.mapperClass);started = true;// Start our subordinate components, if anyif ((loader != null) && (loader instanceof Lifecycle))((Lifecycle) loader).start();if ((logger != null) && (logger instanceof Lifecycle))((Lifecycle) logger).start();if ((manager != null) && (manager instanceof Lifecycle))((Lifecycle) manager).start();if ((cluster != null) && (cluster instanceof Lifecycle))((Lifecycle) cluster).start();if ((realm != null) && (realm instanceof Lifecycle))((Lifecycle) realm).start();if ((resources != null) && (resources instanceof Lifecycle))((Lifecycle) resources).start();// Start our Mappers, if anyMapper mappers[] = findMappers();for (int i = 0; i < mappers.length; i++) {if (mappers[i] instanceof Lifecycle)((Lifecycle) mappers[i]).start();}// Start our child containers, if anyContainer children[] = findChildren();for (int i = 0; i < children.length; i++) {if (children[i] instanceof Lifecycle)((Lifecycle) children[i]).start();}// Start the Valves in our pipeline (including the basic), if anyif (pipeline instanceof Lifecycle)((Lifecycle) pipeline).start();// Notify our interested LifecycleListenerslifecycle.fireLifecycleEvent(START_EVENT, null);// Notify our interested LifecycleListenerslifecycle.fireLifecycleEvent(AFTER_START_EVENT, null);}

2）StandardHostMapper类中最重要的方法是 map()方法，源代码如下：

      public Container map(Request request, boolean update) { //org.apache.catalina.core.StandardHostMapper.map()// Has this request already been mapped?if (update && (request.getContext() != null))return (request.getContext());// Perform mapping on our request URIString uri = ((HttpRequest) request).getDecodedRequestURI();Context context = host.map(uri); // highlight line.// Update the request (if requested) and return the selected Contextif (update) {request.setContext(context);if (context != null)((HttpRequest) request).setContextPath(context.getPath());else((HttpRequest) request).setContextPath(null);}return (context);}

Attention）StandardHostMapper.map()方法仅仅调用了 Host.map()方法；

【4】StandardHostValve类（org.apache.catalina.core.StandardHostValve）

1）StandardHostValve是StandardHost 的基础阀。当有引入的http 请求时，会调用 StandardHostValve.invoke()方法对其进行处理；

public void invoke(Request request, Response response,ValveContext valveContext)  //org.apache.catalina.core.StandardHostValve.invoke().throws IOException, ServletException {// Validate the request and response object typesif (!(request.getRequest() instanceof HttpServletRequest) ||!(response.getResponse() instanceof HttpServletResponse)) {return;     // NOTE - Not much else we can do generically}// Select the Context to be used for this RequestStandardHost host = (StandardHost) getContainer();Context context = (Context) host.map(request, true); // highlight line.if (context == null) {((HttpServletResponse) response.getResponse()).sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,sm.getString("standardHost.noContext"));return;}// Bind the context CL to the current threadThread.currentThread().setContextClassLoader(context.getLoader().getClassLoader());// Update the session last access time for our session (if any)HttpServletRequest hreq = (HttpServletRequest) request.getRequest();String sessionId = hreq.getRequestedSessionId();if (sessionId != null) {Manager manager = context.getManager();if (manager != null) {Session session = manager.findSession(sessionId);if ((session != null) && session.isValid())session.access(); //highlight line.}}// Ask this Context to process this requestcontext.invoke(request, response);Thread.currentThread().setContextClassLoader(StandardHostValve.class.getClassLoader());}

对以上代码的分析（Analysis）：

step1）在tomcat4中，首先invoke()方法会调用 StandardHost.map() 方法来获取一个相应的 Context实例；
// Select the Context to be used for this RequestStandardHost host = (StandardHost) getContainer();Context context = (Context) host.map(request, true); // highlight line.

Attention）在获取Context实例的代码中有一个往复的过程。上面的map()方法需要两个参数，该方法定义在 ContainerBase类中。ContainerBase.map()方法会找到其子容器的映射器，并调用其map()方法；

step2）然后，invoke()方法会获取与该request对象相关联的session 对象，并调用其 access()方法。access()方法会修改 session对象的最后访问时间。

step3）org.apache.catalina.session.StandardSession.access()方法的源代码如下：
 public void access() {this.isNew = false;this.lastAccessedTime = this.lastUsedTime;this.lastUsedTime = System.currentTimeMillis();}
step4）最后StandardHostValve.invoke()方法调用Context实例的 invoke()来处理http 请求；

【5】为什么必须要有一个Host容器

1）在tomcat4 和 tomcat5的部署中，若一个Context实例使用ContextConfig对象进行设置，就必须使用一个 Host对象，原因如下（reasons）：

r1）使用ContextConfig对象需要知道应用程序 web.xml 文件的位置。在其 applicationConfig() 方法中，它会试图打开web.xml ；applicationConfig()方法的源码片段如下：

private void applicationConfig() { // org.apache.catalina.startup.ContextConfig.applicationConfig()// Open the application web.xml file, if it existsInputStream stream = null;ServletContext servletContext = context.getServletContext();if (servletContext != null)stream = servletContext.getResourceAsStream(Constants.ApplicationWebXml); //  public static final String ApplicationWebXml = "/WEB-INF/web.xml";if (stream == null) {log(sm.getString("contextConfig.applicationMissing"));return;}// Process the application web.xml filesynchronized (webDigester) { // highlight code begins.try {URL url =servletContext.getResource(Constants.ApplicationWebXml);InputSource is = new InputSource(url.toExternalForm());is.setByteStream(stream);webDigester.setDebug(getDebug());if (context instanceof StandardContext) {((StandardContext) context).setReplaceWelcomeFiles(true);}webDigester.clear();webDigester.push(context);webDigester.parse(is);webDigester.push(null);} catch (SAXParseException e) {log(sm.getString("contextConfig.applicationParse"), e);log(sm.getString("contextConfig.applicationPosition","" + e.getLineNumber(),"" + e.getColumnNumber()));ok = false;} catch (Exception e) {log(sm.getString("contextConfig.applicationParse"), e);ok = false;} finally {try {if (stream != null) {stream.close();}} catch (IOException e) {log(sm.getString("contextConfig.applicationClose"), e);}}        }    }<strong style="font-family: SimSun; background-color: rgb(255, 255, 255);"> </strong>

对以上代码的分析（Analysis）：

A1）其中public static final String ApplicationWebXml = "/WEB-INF/web.xml"；web.xml 文件的相对路径，servletContext是一个 org.apache.catalina.core.ApplicationContext类型（实现了 javax.servlet.servletContext接口）的对象；

A2）下面是 ApplicationContext.getResource()方法的部分实现代码：
public URL getResource(String path)  throws MalformedURLException { // org.apache.catalina.core.ApplicationContext.getResource(). path = normalize(path);if (path == null)return (null);DirContext resources = context.getResources();if (resources != null) {String fullPath = context.getName() + path;String hostName = context.getParent().getName(); //highlight line.try {resources.lookup(path);if( System.getSecurityManager() != null ) {try {PrivilegedGetResource dp =new PrivilegedGetResource(hostName, fullPath, resources);return (URL)AccessController.doPrivileged(dp);} catch( PrivilegedActionException pe) {throw pe.getException();}} else {return new URL("jndi", null, 0, getJNDIUri(hostName, fullPath),new DirContextURLStreamHandler(resources));}} catch (Exception e) {//e.printStackTrace();}}return (null);}
Attention）上述“highlight line” 所标识的行表明了，如果要使用 ContextConfig实例来进行配置的话，Context实例必须有一个 Host实例作为其父容器，否则context.getParent().getName()会抛出异常导致获取资源文件（web.xml）的URL不成功；

【6】应用程序1（StandardHost测试用例）

6.1）源代码

public final class Bootstrap1 {public static void main(String[] args) {//invoke: http://localhost:8080/app1/Primitive or http://localhost:8080/app1/ModernSystem.setProperty("catalina.base", System.getProperty("user.dir"));Connector connector = new HttpConnector();Wrapper wrapper1 = new StandardWrapper();wrapper1.setName("Primitive");//wrapper1.setServletClass("servlet.PrimitiveServlet");wrapper1.setServletClass("PrimitiveServlet");Wrapper wrapper2 = new StandardWrapper();wrapper2.setName("Modern");//wrapper2.setServletClass("servlet.ModernServlet");wrapper2.setServletClass("ModernServlet");Context context = new StandardContext();// StandardContext's start method adds a default mappercontext.setPath("/app1");context.setDocBase("app1");context.addChild(wrapper1);context.addChild(wrapper2);LifecycleListener listener = new SimpleContextConfig();((Lifecycle) context).addLifecycleListener(listener);Host host = new StandardHost();host.addChild(context);host.setName("localhost");host.setAppBase("webapps");Loader loader = new WebappLoader();context.setLoader(loader);// context.addServletMapping(pattern, name);context.addServletMapping("/Primitive", "Primitive");context.addServletMapping("/Modern", "Modern");connector.setContainer(host);try {connector.initialize();((Lifecycle) connector).start();((Lifecycle) host).start(); // 与以往的Bootstrap.java不同的是，这里是host.start() 而不是 context.start()// make the application wait until we press a key.System.in.read();((Lifecycle) host).stop();}catch (Exception e) {e.printStackTrace();}}
}

对以上代码的分析（Analysis）：

A1）本文结合 “tomcat(11)的Tomcat 处理http请求的方法调用协作图（以Context容器为起点）”总结了“《Tomcat 处理http请求的方法调用协作图（以Host容器为起点）》”，如下：

6.2）console info

E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src>java -cp .;lib/servlet.jar;lib/catalina_4_1_24.jar;lib/catalina-5.5.4.jar;lib/naming-common
jar;lib/commons-collections.jar;lib/naming-resources.jar;lib/commons-digester.jar;lib/catalina.jar;E:\bench-cluster\cloud-data-preprocess\HowTomcatWo
ks\webroot com.tomcat.chapter13.startup.Bootstrap1
HttpConnector Opening server socket on all host IP addresses
HttpConnector[8080] Starting background thread
WebappLoader[/app1]: Deploying class repositories to work directory E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src\work\_\localhost\app1
StandardManager[/app1]: Seeding random number generator class java.security.SecureRandom
StandardManager[/app1]: Seeding of random number generator has been completed
StandardManager[/app1]: IOException while loading persisted sessions: java.io.EOFException
java.io.EOFException // <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); font-family: Consolas, 'Courier New', Courier, mono, serif; line-height: 18px;">这是从文件中加载 session对象到内存，由于没有相关文件，所以加载失败，抛出异常，但这不会影响我们访问servlet，大家不要惊慌；  </span><span style="margin: 0px; padding: 0px; border: none; font-family: Consolas, 'Courier New', Courier, mono, serif; line-height: 18px;">  </span>at java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1188)at org.apache.catalina.core.StandardHost.start(StandardHost.java:738)at com.tomcat.chapter13.startup.Bootstrap1.main(Bootstrap1.java:59)
StandardManager[/app1]: Exception loading sessions from persistent storage
java.io.EOFExceptionat java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1188)at org.apache.catalina.core.StandardHost.start(StandardHost.java:738)at com.tomcat.chapter13.startup.Bootstrap1.main(Bootstrap1.java:59)
ModernServlet -- init
StandardHost[localhost]: MAPPING configuration error for request URI /favicon.ico

6.3）访问效果

【7】Engine接口（org.apche.catalina.Engine）

1）intro to Engine：Engine容器是org.apche.catalina.Engine接口的实例。Engine容器也就是tomcat的servlet 引擎。当部署tomcat时要支持多个虚拟机（Host）的话，就需要使用 Engine容器。一般 case下，部署的tomcat 都会使用一个 Engine容器；

2）org.apche.catalina.Engine定义如下：

public interface Engine extends Container {  public String getDefaultHost();  public void setDefaultHost(String defaultHost);  public String getJvmRoute();  public void setJvmRoute(String jvmRouteId);  public Service getService();  public void setService(Service service);   public void addDefaultContext(DefaultContext defaultContext);   public DefaultContext getDefaultContext();  public void importDefaultContext(Context context);
}

3）在Engine容器中，可以设置一个默认的Host容器或Context容器。注意，Engine容器可以与一个服务实例相关联；

【8】StandardEngine类（org.apache.catalina.core.StandardEngine）

1）其构造函数如下：

public class StandardEngine  extends ContainerBase implements Engine { public StandardEngine() { super();pipeline.setBasic(new StandardEngineValve());}

2）作为一个顶层容器，Engine容器可以有子容器，而它的子容器只能是Host容器；将一个非Host容器设置为其子容器，则抛出异常，参见StandardEngine.addChild()：

public void addChild(Container child) { // org.apache.catalina.core.StandardEngine.addChild().if (!(child instanceof Host))throw new IllegalArgumentException(sm.getString("standardEngine.notHost"));super.addChild(child);}

3）当然了，由于Engine是顶层容器，它就不能再有父容器了，若调用 StandardEngine.setParent方法为其设置父容器时，抛出异常：

 public void setParent(Container container) {   // org.apache.catalina.core.StandardEngine.setParent().throw new IllegalArgumentException(sm.getString("standardEngine.notParent"));}

【9】StandardEngineValve类（org.apache.catalina.core.StandardEngineValve）

1）StandardEngineValve：是 StandardEngine容器的基础阀；

2）StandardEngineValve.invoke()方法如下：

 public void invoke(Request request, Response response,ValveContext valveContext) // org.apache.catalina.core.StandardEngineValve.invoke().throws IOException, ServletException {// Validate the request and response object typesif (!(request.getRequest() instanceof HttpServletRequest) ||!(response.getResponse() instanceof HttpServletResponse)) {return;     // NOTE - Not much else we can do generically}// Validate that any HTTP/1.1 request included a host headerHttpServletRequest hrequest = (HttpServletRequest) request;if ("HTTP/1.1".equals(hrequest.getProtocol()) &&(hrequest.getServerName() == null)) {((HttpServletResponse) response.getResponse()).sendError(HttpServletResponse.SC_BAD_REQUEST,sm.getString("standardEngine.noHostHeader",request.getRequest().getServerName()));return;}// Select the Host to be used for this RequestStandardEngine engine = (StandardEngine) getContainer();Host host = (Host) engine.map(request, true);if (host == null) {((HttpServletResponse) response.getResponse()).sendError(HttpServletResponse.SC_BAD_REQUEST,sm.getString("standardEngine.noHost",request.getRequest().getServerName()));return;}// Ask this Host to process this requesthost.invoke(request, response);}

对以上代码的分析（Analysis）：

step1）在验证了request和response对象的类型后，invoke()方法得到Host实例，用于处理该请求；

step2）invoke()方法会通过调用Engine实例的map()方法获取Host对象；

step3）得到Host对象后，调用其invoke() 方法处理请求；

【10】应用程序2（StandardEngine测试用例）

1）源代码：

public final class Bootstrap2 {public static void main(String[] args) {//invoke: http://localhost:8080/app1/Primitive or http://localhost:8080/app1/ModernSystem.setProperty("catalina.base", System.getProperty("user.dir"));Connector connector = new HttpConnector();Wrapper wrapper1 = new StandardWrapper();wrapper1.setName("Primitive");//wrapper1.setServletClass("servlet.PrimitiveServlet");wrapper1.setServletClass("PrimitiveServlet");Wrapper wrapper2 = new StandardWrapper();wrapper2.setName("Modern");//wrapper2.setServletClass("servlet.ModernServlet");wrapper2.setServletClass("ModernServlet");Context context = new StandardContext();// StandardContext's start method adds a default mappercontext.setPath("/app1");context.setDocBase("app1");context.addChild(wrapper1);context.addChild(wrapper2);LifecycleListener listener = new SimpleContextConfig();((Lifecycle) context).addLifecycleListener(listener);Host host = new StandardHost();host.addChild(context);host.setName("localhost");host.setAppBase("webapps");Loader loader = new WebappLoader();context.setLoader(loader);// context.addServletMapping(pattern, name);context.addServletMapping("/Primitive", "Primitive");context.addServletMapping("/Modern", "Modern");Engine engine = new StandardEngine();engine.addChild(host);engine.setDefaultHost("localhost");connector.setContainer(engine);try {connector.initialize();((Lifecycle) connector).start();((Lifecycle) engine).start();// make the application wait until we press a key.System.in.read();((Lifecycle) engine).stop(); // 与以往不同的是，这里是engine.start()而不是 context.start()，因为最上层容易已经改变了，而enginge包含host，host包含context，context包含wrapper.}catch (Exception e) {e.printStackTrace();}}
}

对以上代码的分析（Analysis）：

A1）同理，本小节也总结了 “Tomcat 处理http请求的方法调用协作图（以Engine容器为起点）”，如下：

A2）对上面的协作图的调用steps做分析：

step1）当http 请求到达 tomcat server时，HttpConnector得到 ServerSocket(（accept()方法）），然后调用最上层容器的invoke（）方法，而所有容器都继承自ContainerBase，所以实际上调用的是 ContainerBase.invoke（）方法；

step2）之后调用管道StandardPipeline.invoke()方法，进而调用管道的非基础阀和基础阀的invoke方法（而基础阀在容器的构造器中设置了）；（干货——所有容器都继承自ContainerBase，而管道StandardPipeline是在 ContainerBase中创建的，所以所有容器都共用同一个管道对象，而当调用到某容器的时候，设置其对应的基础阀即可）

step3）基础阀的invoke()方法会调用下一层级容器的invoke方法，接着继续调用管道StandardPipeline.invoke()方法，一直进行下去（回到step2的过程）.......直到到达Wrapper容器（因为它是最小的容器，是一个具体servlet的封装）；

step4）Wrapper.invoke（）方法，同样也要调用其管道StandardPipeline.invoke()方法，接着调用基础阀StandardWrapperValve，与其他基础阀不同的是，StandardWrapperValve.invoke()方法会调用 ApplicationFilterChain.doFilter()方法，接着调用具体的HttpServlet.allocate()方法和service()方法，写出响应info（html）到client，ending（Bingo）；

2）console info

E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src>java -cp .;lib/servlet.jar;lib/catalina_4_1_24.jar;lib/catalina-5.5.4.jar;lib/naming-common.
jar;lib/commons-collections.jar;lib/naming-resources.jar;lib/commons-digester.jar;lib/catalina.jar;E:\bench-cluster\cloud-data-preprocess\HowTomcatWok
s\webroot com.tomcat.chapter13.startup.Bootstrap2
HttpConnector Opening server socket on all host IP addresses
HttpConnector[8080] Starting background thread
Apache Tomcat/4.1.24
WebappLoader[/app1]: Deploying class repositories to work directory E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src\work\_\localhost\app1
WebappLoader[/app1]: Deploy class files /WEB-INF/classes to E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src\webapps\app1\WEB-INF\classes
StandardManager[/app1]: Seeding random number generator class java.security.SecureRandom
StandardManager[/app1]: Seeding of random number generator has been completed
StandardManager[/app1]: IOException while loading persisted sessions: java.io.EOFException
java.io.EOFExceptionat java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1188)at org.apache.catalina.core.StandardHost.start(StandardHost.java:738)at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1188)at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:347)at com.tomcat.chapter13.startup.Bootstrap2.main(Bootstrap2.java:67)
StandardManager[/app1]: Exception loading sessions from persistent storage
java.io.EOFExceptionat java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1188)at org.apache.catalina.core.StandardHost.start(StandardHost.java:738)at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1188)at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:347)at com.tomcat.chapter13.startup.Bootstrap2.main(Bootstrap2.java:67)
ModernServlet -- init
StandardHost[localhost]: MAPPING configuration error for request URI /favicon.ico
StandardHost[localhost]: MAPPING configuration error for request URI /favicon.ico

3）访问效果