tomcat(12)org.apache.catalina.core.StandardContext源码剖析

【0】README

0）本文部分文字描述转自 “how tomcat works”，旨在学习 “tomcat(12)StandardContext源码剖析” 的基础知识；

1）Context实例表示一个具体的web 应用程序，其中包含一个或多个Wrapper实例，每个Wrapper 表示一个具体的servlet定义；

2）Context容器还需要其他组件的支持，如载入器和Session 管理器。本章要intro 的 StandardContext是 catalina中Context接口的标准实现；

3）本文首先会回顾StandardContext类的实例化和配置，然后讨论与其相关的StandardMapper类和 ContextConfig类。接下来，学习对于引入的每个HTTP 请求的方法调用序列；

【1】StardardContext 配置

1）intro：创建了StandardContext实例后，必须调用其start() 方法来为引入的每个http 请求提供服务；

1.1）StandardContext对象可能启动失败：这时available 设置为false，该属性表明StandardContext 对象是否可用；

1.2）若启动成功：available=true，则表明StandardContext 对象配置正确；

2）正确配置StandardContext后，StandardContext才能读入并解析默认的 web.xml文件，该文件位于 %CATALINA_HOME%/conf 目录下，该文件的内容会应用到所有部署到tomcat 中的应用程序中。这也保证了StandardContext 实例可以处理应用程序级的web.xml 文件；

3）StandardContext.configured属性：表明StandardContext 实例是否正确配置

3.1）StandardContext使用了一个事件监听器作为其配置器；（干货——StandardContext使用了一个事件监听器作为其配置器，参见下图中StandardContext.start()方法中lifecycle.fireLifecycleEvent(BEFORE_START_EVENT, null) 调用）

3.2）当调用StandardContext.start()方法时，其中要做的一件事情是，触发一个生命周期事件。该事件调用监听器，对StandardContext实例进行配置；

3.3）若配置成功，则监听器将 configured设置为true，否则StandardContext 实例拒绝启动，也就无法为http 请求提供服务了；

Attention）下面的图片借用了 “tomcat(10)安全性中章节【6.4】中Supplement-补充模块”的第1张图；

【1.1】StandardContext 类的构造函数

1）源代码如下：

public StandardContext() { // org.apache.catalina.core.StandardContext.StandardContext().super();pipeline.setBasic(new StandardContextValve());namingResources.setContainer(this);}

2）构造函数最重要的事情：是为 StandardContext 实例的管道对象设置基础阀；

【1.2】启动StandardContext 实例

1）start()方法会初始化 StandardContext对象，用生命周期监听器配置 StandardContext实例；

1.1）StandardContext 对象可能启动失败：这时available 设置为false，该属性表明StandardContext 对象是否可用；

1.2）若启动成功：available=true，则表明StandardContext 对象配置正确，与其关联的子容器和组件都正确启动；

2）正确配置后，StandardContext实例可以准备为引入的 http 请求提供服务了。若期间发生了错误，则available设置为false；

3）StandardContext.configured属性：表明StandardContext 实例是否正确配置

3.1）在start()方法的末尾， StandardContext实例会检查 configured变量的值，若configured设置为 true，则StandardContext 启动成功；

3.2）否则，调用stop() 方法，关闭在start() 方法已经启动的所有组件；

public synchronized void start() throws LifecycleException { //org.apache.catalina.core.StandardContext.start()方法if (started)throw new LifecycleException(sm.getString("containerBase.alreadyStarted", logName()));if (debug >= 1)log("Starting");// Notify our interested LifecycleListenerslifecycle.fireLifecycleEvent(BEFORE_START_EVENT, null);if (debug >= 1)log("Processing start(), current available=" + getAvailable());setAvailable(false);setConfigured(false);boolean ok = true;// Add missing components as necessaryif (webappResources == null) {   // (1) Required by Loaderif (debug >= 1)log("Configuring default Resources");try {if ((docBase != null) && (docBase.endsWith(".war")))setResources(new WARDirContext());elsesetResources(new FileDirContext());} catch (IllegalArgumentException e) {log("Error initializing resources: " + e.getMessage());ok = false;}}if (ok) {if (!resourcesStart())ok = false;}// Install DefaultContext configurationif (!getOverride()) {Container host = getParent();if (host instanceof StandardHost) {((StandardHost)host).installDefaultContext(this);Container engine = host.getParent();if( engine instanceof StandardEngine ) {((StandardEngine)engine).installDefaultContext(this);}}}if (getLoader() == null) {      // (2) Required by Managerif (getPrivileged()) {if (debug >= 1)log("Configuring privileged default Loader");setLoader(new WebappLoader(this.getClass().getClassLoader()));} else {if (debug >= 1)log("Configuring non-privileged default Loader");setLoader(new WebappLoader(getParentClassLoader()));}}if (getManager() == null) {     // (3) After prerequisitesif (debug >= 1)log("Configuring default Manager");setManager(new StandardManager());}// Initialize character set mappergetCharsetMapper();// Post work directorypostWorkDirectory();// Reading the "catalina.useNaming" environment variableString useNamingProperty = System.getProperty("catalina.useNaming");if ((useNamingProperty != null)&& (useNamingProperty.equals("false"))) {useNaming = false;}if (ok && isUseNaming()) {if (namingContextListener == null) {namingContextListener = new NamingContextListener();namingContextListener.setDebug(getDebug());namingContextListener.setName(getNamingContextName());addLifecycleListener(namingContextListener);}}// Binding threadClassLoader oldCCL = bindThread();// Standard container startupif (debug >= 1)log("Processing standard container startup");if (ok) {try {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();// Unbinding threadunbindThread(oldCCL);// Binding threadoldCCL = bindThread();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);if ((manager != null) && (manager instanceof Lifecycle))((Lifecycle) manager).start();} finally {// Unbinding threadunbindThread(oldCCL);}}if (!getConfigured())ok = false;// We put the resources into the servlet contextif (ok)getServletContext().setAttribute(Globals.RESOURCES_ATTR, getResources());// Binding threadoldCCL = bindThread();// Create context attributes that will be requiredif (ok) {if (debug >= 1)log("Posting standard context attributes");postWelcomeFiles();}// Configure and call application event listeners and filtersif (ok) {if (!listenerStart())ok = false;}if (ok) {if (!filterStart())ok = false;}// Unbinding threadunbindThread(oldCCL);// Set available status depending upon startup successif (ok) {if (debug >= 1)log("Starting completed");setAvailable(true);} else {log(sm.getString("standardContext.startFailed"));try {stop();} catch (Throwable t) {log(sm.getString("standardContext.startCleanup"), t);}setAvailable(false);throw new LifecycleException(sm.getString("standardContext.startFailed"));}// Notify our interested LifecycleListenerslifecycle.fireLifecycleEvent(AFTER_START_EVENT, null);// Load and initialize all "load on startup" servletsoldCCL = bindThread();loadOnStartup(findChildren());unbindThread(oldCCL);}

对以上代码的调用过程进行分析-start()方法需要完成以下工作（works）：

work1）触发 BEFORE_START 事件；

 public synchronized void start() throws LifecycleException { //org.apache.catalina.core.StandardContext.start()方法。if (started)throw new LifecycleException(sm.getString("containerBase.alreadyStarted", logName()));if (debug >= 1)log("Starting");// Notify our interested LifecycleListenerslifecycle.fireLifecycleEvent(BEFORE_START_EVENT, null);

work2）将 availability 属性设置为false；

work3）将 configured 属性设置为 false；

 if (debug >= 1)log("Processing start(), current available=" + getAvailable());setAvailable(false);setConfigured(false);boolean ok = true;

work4）配置资源；

// Add missing components as necessaryif (webappResources == null) {   // (1) Required by Loaderif (debug >= 1)log("Configuring default Resources");try {if ((docBase != null) && (docBase.endsWith(".war")))setResources(new WARDirContext());elsesetResources(new FileDirContext());} catch (IllegalArgumentException e) {log("Error initializing resources: " + e.getMessage());ok = false;}}if (ok) {if (!resourcesStart())ok = false;}// Install DefaultContext configurationif (!getOverride()) {Container host = getParent();if (host instanceof StandardHost) {((StandardHost)host).installDefaultContext(this);Container engine = host.getParent();if( engine instanceof StandardEngine ) {((StandardEngine)engine).installDefaultContext(this);}}}

work5）设置载入器；

if (getLoader() == null) {      // (2) Required by Managerif (getPrivileged()) {if (debug >= 1)log("Configuring privileged default Loader");setLoader(new WebappLoader(this.getClass().getClassLoader()));} else {if (debug >= 1)log("Configuring non-privileged default Loader");setLoader(new WebappLoader(getParentClassLoader()));}}

work6）设置Session 管理器；

 if (getManager() == null) {     // (3) After prerequisitesif (debug >= 1)log("Configuring default Manager");setManager(new StandardManager());}

work7）初始化字符集映射器；

// Initialize character set mappergetCharsetMapper(); // defined in start().public CharsetMapper getCharsetMapper() {// Create a mapper the first time it is requestedif (this.charsetMapper == null) {try {Class clazz = Class.forName(charsetMapperClass);this.charsetMapper =(CharsetMapper) clazz.newInstance();} catch (Throwable t) {this.charsetMapper = new CharsetMapper();}}return (this.charsetMapper);}

work8）启动与该Context 容器相关联的组件；

// Post work directorypostWorkDirectory();
// Reading the "catalina.useNaming" environment variableString useNamingProperty = System.getProperty("catalina.useNaming");if ((useNamingProperty != null)&& (useNamingProperty.equals("false"))) {useNaming = false;}if (ok && isUseNaming()) {if (namingContextListener == null) {namingContextListener = new NamingContextListener();namingContextListener.setDebug(getDebug());namingContextListener.setName(getNamingContextName());addLifecycleListener(namingContextListener);}}// Binding threadClassLoader oldCCL = bindThread();

work9）启动子容器；

work10）启动管道对象；

work11）启动Session 管理器；

work12）触发 START 事件，在这里监听器（ContextConfig 实例）会执行一些配置操作，若配置成功，ContextConfig 实例会将 StandardContext.configured 变量设置为 true；

 // Set available status depending upon startup successif (ok) {if (debug >= 1)log("Starting completed");setAvailable(true);} else {log(sm.getString("standardContext.startFailed"));try {stop();} catch (Throwable t) {log(sm.getString("standardContext.startCleanup"), t);}setAvailable(false);throw new LifecycleException(sm.getString("standardContext.startFailed"));}

work13）检查 configured 属性的值，若为true，则调用 postWelcomePages()方法，载入那些需要在启动时就载入的子容器，即 Wrapper实例，将 availability属性设置为 true。若 configured 变量为false，则调用stop() 方法；

 // Create context attributes that will be requiredif (ok) { // defined in start() method.if (debug >= 1)log("Posting standard context attributes");postWelcomeFiles();}private void postWelcomeFiles() {getServletContext().setAttribute("org.apache.catalina.WELCOME_FILES",welcomeFiles);}

work14）触发 AFTER_START 事件；

 // Notify our interested LifecycleListenerslifecycle.fireLifecycleEvent(AFTER_START_EVENT, null); // highlight line.// Load and initialize all "load on startup" servletsoldCCL = bindThread();loadOnStartup(findChildren());unbindThread(oldCCL);

【1.3】 org.apahce.catalina.core.StandardContext.invoke() 方法

1）该方法首先会检查应用程序是否正在重载过程中，若是，则等待应用程序重载完成。然后，它调用其父类的 ContainerBase.invoke() 方法；

public void invoke(Request request, Response response)  throws IOException, ServletException { // Wait if we are reloadingwhile (getPaused()) {  // 返回 paused属性的值，当paused为true时，表明应用程序正在重载；try {Thread.sleep(1000);} catch (InterruptedException e) {;}}// Normal request processingif (swallowOutput) {try {SystemLogHandler.startCapture();super.invoke(request, response);} finally {String log = SystemLogHandler.stopCapture();if (log != null && log.length() > 0) {log(log);}}} else {super.invoke(request, response);}}

Attention）上述的StandardContext.invoke() 方法是tomcat 4中的实现，而在 tomcat5中，StandardContext 并没有提供 invoke()方法的实现，所以会执行 ContainerBase.invoke() 方法；而检查应用程序是否正在重载的工作移到了 StandardContextValve.invoke() 方法中；

【2】StandardContextMapper 类

1）对于每个引入的http 请求，都会调用 StandardContext实例的管道对象的基础阀的invoke() 方法来处理；

1.1）StandardContext 实例的基础阀：是 org.apache.catalina.core.StandardContextValve 类的实例；

1.2）StandardContextValve.invoke()方法要做的第一件事：是获取一个要处理 http 请求的Wrapper 实例；

2）在tomcat4中，StandardContextValve实例在它包含的 StandardContext中查找。StandardContextValve实例使用 StandardContext实例的映射器找到一个合适的 Wrapper实例。获得Wrapper实例后，它就会调用 Wrapper.invoke()方法；

3）我们谈谈映射器： ContainerBase类是 StandardContext类的父类，前者定义 addDefaultMapper()方法用来添加一个默认的映射器，如下所示：

protected void addDefaultMapper(String mapperClass) { // org.apache.catalina.core.ContainerBase.addDefaultMapper() method.// Do we need a default Mapper?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);}}

3.2）StandardContext.start()方法中会调用 addDefaultMapper()方法，并传入变量mapperClass的值：

public synchronized void start() throws LifecycleException {// ......if (ok) {try {addDefaultMapper(this.mapperClass);started = true;} //......
// private String mapperClass =  "org.apache.catalina.core.StandardContextMapper";

3.3）必须要调用映射器的setContainer()方法，通过传入一个容器的实例，将映射器和容器相关联。在Catalina中，org.apache.catalina.Mapper 接口的实现类是 org.apache.catalina.core.StandardContextMapper类。StandardContextMapper实例只能与 Context级容器相关联，setContainer()方法如下所示：

public void setContainer(Container container) { // org.apche.catalina.core.StandardContextMapper.setContainer().if (!(container instanceof StandardContext))throw new IllegalArgumentException(sm.getString("httpContextMapper.container"));context = (StandardContext) container;}public StandardContext() { // 而在StandardContext构造中调用setContainer().super();pipeline.setBasic(new StandardContextValve());namingResources.setContainer(this);}

3.4）映射器最重要的方法是map()方法，该方法会返回用来处理http 请求的子容器，该方法签名如下：

public Container map(Request request, boolean update) { // org.apache.catalina.core.StandardContextMapper.map().int debug = context.getDebug();// Has this request already been mapped?if (update && (request.getWrapper() != null))return (request.getWrapper());// Identify the context-relative URI to be mappedString contextPath =((HttpServletRequest) request.getRequest()).getContextPath();String requestURI = ((HttpRequest) request).getDecodedRequestURI();String relativeURI = requestURI.substring(contextPath.length());// Apply the standard request URI mapping rules from the specificationWrapper wrapper = null;String servletPath = relativeURI;String pathInfo = null;String name = null;// Rule 1 -- Exact Match      // Rule 2 -- Prefix Match       // Rule 3 -- Extension Match // Rule 4 -- Default Match       // Update the Request (if requested) and return this Wrapper if ((debug >= 1) && (wrapper != null))context.log(" Mapped to servlet '" + wrapper.getName() +"' with servlet path '" + servletPath +"' and path info '" + pathInfo +"' and update=" + update);if (update) {request.setWrapper(wrapper);((HttpRequest) request).setServletPath(servletPath);((HttpRequest) request).setPathInfo(pathInfo);}return (wrapper);}
}

4）现在，我们回到org.apche.catalina.core.StandardContextValve：其invoke（）方法对于引入的每个http 请求，都会调用Context容器的map()方法，并传入一个 org.apache.catalina.Request 对象。

public void invoke(Request request, Response response,  ValveContext valveContext) throws IOException, ServletException { <span style="font-family: Arial, Helvetica, sans-serif;">//org.apche.catalina.core.StandardContextValve.invoke().</span>// .....        // Disallow any direct access to resources under WEB-INF or META-INFHttpServletRequest hreq = (HttpServletRequest) request.getRequest();String contextPath = hreq.getContextPath();String requestURI = ((HttpRequest) request).getDecodedRequestURI();String relativeURI =requestURI.substring(contextPath.length()).toUpperCase();//......Context context = (Context) getContainer();Wrapper wrapper = null;try {wrapper = (Wrapper) context.map(request, true); // highlight line.->ContainerBase.map().} //......// Ask this Wrapper to process this Requestresponse.setContext(context);wrapper.invoke(request, response);  }

4.1）map() 方法会针对某个特定的协议调用 findMapper()方法返回一个映射器对象，然后调用映射器对象的map() 方法获取 Wrapper实例；

public Container map(Request request, boolean update) {// Select the Mapper we will useMapper mapper = findMapper(request.getRequest().getProtocol());if (mapper == null)return (null);// Use this Mapper to perform this mappingreturn (mapper.map(request, update));
}public Mapper findMapper(String protocol) {if (mapper != null)return (mapper); // mapper == StandardContextMapperelsesynchronized (mappers) {return ((Mapper) mappers.get(protocol));}}

4.2）下面对org.apache.catalina.core.StandardContextMapper.map()方法的调用过程进行分析：

step1）会先标识出相对于Context的URL：

step2）然后，它试图应用匹配规则找到一个适合的Wrapper实例；

Attention）以上代码的都是基于tomcat4在做分析，而在tomcat5中，Mapper接口及其相关类已经被移除了。事实上，StandardContextValve.invoke()方法会从 request对象中获取适合的 Wrapper实例： Wrapper wrapper = reqeust.getWrapper(); （该Wrapper实例指明了封装在 request对象中的映射信息）

// step1 begins.    
public Container map(Request request, boolean update) { // org.apache.catalina.core.StandardContextMapper.map().int debug = context.getDebug();// Has this request already been mapped?if (update && (request.getWrapper() != null))return (request.getWrapper());// Identify the context-relative URI to be mappedString contextPath =((HttpServletRequest) request.getRequest()).getContextPath();String requestURI = ((HttpRequest) request).getDecodedRequestURI();String relativeURI = requestURI.substring(contextPath.length());if (debug >= 1)context.log("Mapping contextPath='" + contextPath +"' with requestURI='" + requestURI +"' and relativeURI='" + relativeURI + "'");
// step1 ends.
// step2 begins.
// Apply the standard request URI mapping rules from the specificationWrapper wrapper = null;String servletPath = relativeURI;String pathInfo = null;String name = null;// Rule 1 -- Exact Matchif (wrapper == null) {if (debug >= 2)context.log("  Trying exact match");if (!(relativeURI.equals("/")))name = context.findServletMapping(relativeURI);if (name != null)wrapper = (Wrapper) context.findChild(name); //highlight line.if (wrapper != null) {servletPath = relativeURI;pathInfo = null;}}// Rule 2 -- Prefix Matchif (wrapper == null) {if (debug >= 2)context.log("  Trying prefix match");servletPath = relativeURI;while (true) {name = context.findServletMapping(servletPath + "/*");if (name != null)wrapper = (Wrapper) context.findChild(name); // highlight line.if (wrapper != null) {pathInfo = relativeURI.substring(servletPath.length());if (pathInfo.length() == 0)pathInfo = null;break;}int slash = servletPath.lastIndexOf('/');if (slash < 0)break;servletPath = servletPath.substring(0, slash);}}// Rule 3 -- Extension Matchif (wrapper == null) {if (debug >= 2)context.log("  Trying extension match");int slash = relativeURI.lastIndexOf('/');if (slash >= 0) {String last = relativeURI.substring(slash);int period = last.lastIndexOf('.');if (period >= 0) {String pattern = "*" + last.substring(period);name = context.findServletMapping(pattern); // highlight line.if (name != null)wrapper = (Wrapper) context.findChild(name);if (wrapper != null) {servletPath = relativeURI;pathInfo = null;}}}}// Rule 4 -- Default Matchif (wrapper == null) {if (debug >= 2)context.log("  Trying default match");name = context.findServletMapping("/");if (name != null)wrapper = (Wrapper) context.findChild(name); //highlight line.if (wrapper != null) {servletPath = relativeURI;pathInfo = null;}}
// step2 ends.
// step3 begins.// Update the Request (if requested) and return this Wrapperif ((debug >= 1) && (wrapper != null))context.log(" Mapped to servlet '" + wrapper.getName() +"' with servlet path '" + servletPath +"' and path info '" + pathInfo +"' and update=" + update);if (update) {request.setWrapper(wrapper);((HttpRequest) request).setServletPath(servletPath);((HttpRequest) request).setPathInfo(pathInfo);}return (wrapper);}

对以上代码的分析（Analysis）：以上代码演示了通过 StandardContext.start()方法如何找到映射器和利用 URI 等信息来找到相应的Wrapper容器的；（Bootstrap.main() 设置了相应的child）

【3】对重载的支持

1）启用重载功能：StandardContext.reloadable 属性指明该应用程序是否启用了重载功能。当启用了之后，当 web.xml 文件发生变化或 WEB-INF/classes 目录下的其中一个文件被重新编译后，应用程序会重载；

2）StandardContext是通过其载入器实现应用程序重载的： 在 tomcat4中，StandardContext对象中的 WebappLoader类实现了 Loader接口，并使用另一个线程检查 WEB-INF 目录中的所有类和JAR 文件的时间戳。只需要调用其 setContainer()方法将 WebappLoader 对象与 StandardContext 对象相关联就可以启动该检查线程。

public synchronized void reload() { //org.apache.catalina.core.StandardContext.reload().// Validate our current component stateif (!started)throw new IllegalStateException(sm.getString("containerBase.notStarted", logName()));// Make sure reloading is enabled//      if (!reloadable)//          throw new IllegalStateException//              (sm.getString("standardContext.notReloadable"));log(sm.getString("standardContext.reloadingStarted"));// Stop accepting requests temporarilysetPaused(true);// Binding threadClassLoader oldCCL = bindThread();// Shut down our session managerif ((manager != null) && (manager instanceof Lifecycle)) {try {((Lifecycle) manager).stop();} catch (LifecycleException e) {log(sm.getString("standardContext.stoppingManager"), e);}}// Shut down the current version of all active servletsContainer children[] = findChildren();for (int i = 0; i < children.length; i++) {Wrapper wrapper = (Wrapper) children[i];if (wrapper instanceof Lifecycle) {try {((Lifecycle) wrapper).stop();} catch (LifecycleException e) {log(sm.getString("standardContext.stoppingWrapper",wrapper.getName()),e);}}}// Shut down application event listenerslistenerStop();// Clear all application-originated servlet context attributesif (context != null)context.clearAttributes();// Shut down filtersfilterStop();if (isUseNaming()) {// StartnamingContextListener.lifecycleEvent(new LifecycleEvent(this, Lifecycle.STOP_EVENT));}// Binding threadunbindThread(oldCCL);// Shut down our application class loaderif ((loader != null) && (loader instanceof Lifecycle)) {try {((Lifecycle) loader).stop();} catch (LifecycleException e) {log(sm.getString("standardContext.stoppingLoader"), e);}}// Binding threadoldCCL = bindThread();// Restart our application class loaderif ((loader != null) && (loader instanceof Lifecycle)) {try {((Lifecycle) loader).start();} catch (LifecycleException e) {log(sm.getString("standardContext.startingLoader"), e);}}// Binding threadunbindThread(oldCCL);// Create and register the associated naming context, if internal// naming is usedboolean ok = true;if (isUseNaming()) {// StartnamingContextListener.lifecycleEvent(new LifecycleEvent(this, Lifecycle.START_EVENT));}// Binding threadoldCCL = bindThread();// Restart our application event listeners and filtersif (ok) {if (!listenerStart()) {log(sm.getString("standardContext.listenerStartFailed"));ok = false;}}if (ok) {if (!filterStart()) {log(sm.getString("standardContext.filterStartFailed"));ok = false;}}// Restore the "Welcome Files" and "Resources" context attributespostResources();postWelcomeFiles();// Restart our currently defined servletsfor (int i = 0; i < children.length; i++) {if (!ok)break;Wrapper wrapper = (Wrapper) children[i];if (wrapper instanceof Lifecycle) {try {((Lifecycle) wrapper).start();} catch (LifecycleException e) {log(sm.getString("standardContext.startingWrapper",wrapper.getName()),e);ok = false;}}}// Reinitialize all load on startup servletsloadOnStartup(children);// Restart our session manager (AFTER naming context recreated/bound)if ((manager != null) && (manager instanceof Lifecycle)) {try {((Lifecycle) manager).start();} catch (LifecycleException e) {log(sm.getString("standardContext.startingManager"), e);}}// Unbinding threadunbindThread(oldCCL);// Start accepting requests againif (ok) {log(sm.getString("standardContext.reloadingCompleted"));} else {setAvailable(false);log(sm.getString("standardContext.reloadingFailed"));}setPaused(false);// Notify our interested LifecycleListenerslifecycle.fireLifecycleEvent(Context.RELOAD_EVENT, null);}

3）WebappLoader.setContainer()方法的实现代码如下：

public void setContainer(Container container) { // org.apache.catalina.loader.WebappLoader.setContainer().// Deregister from the old Container (if any)if ((this.container != null) && (this.container instanceof Context))((Context) this.container).removePropertyChangeListener(this);// Process this property changeContainer oldContainer = this.container;this.container = container;support.firePropertyChange("container", oldContainer, this.container);// Register with the new Container (if any)if ((this.container != null) && (this.container instanceof Context)) {setReloadable( ((Context) this.container).getReloadable() );((Context) this.container).addPropertyChangeListener(this);}}

对上述代码的分析（Analysis）：看上述代码的最后一个if语句块：如果当前容器是 Context容器，则调用 setRealoadable()方法。这说明，WebappLoader.reloadable 属性的值与 StandardContext.reloadable 属性的值相同；

4）下面是 WebappLoader.setReloadable() 方法的实现代码：

 public void setReloadable(boolean reloadable) {  // org.apache.catalina.loader.WebappLoader.setContainer(). setReloadable()// Process this property changeboolean oldReloadable = this.reloadable;this.reloadable = reloadable;support.firePropertyChange("reloadable",new Boolean(oldReloadable),new Boolean(this.reloadable));// Start or stop our background thread if requiredif (!started)return;if (!oldReloadable && this.reloadable)threadStart();else if (oldReloadable && !this.reloadable)threadStop();}

对上述代码的分析（Analysis）：

A1）若 reloadable 从false 修改为true：则会调用 threadStart()方法；而threadStart()方法会启动一个专用的线程来不断地检查 WEB-INF 目录下的类和 JAR 文件的时间戳；

A2）若reloadable 从 true 修改为false：则调用调用 threadStop() 方法；而threadStop() 方法则会终止该线程；

Attention）在tomcat5中，为支持重载功能而进行的检查类的时间戳的工作改由 backgroundProcess()方法执行；

【4】backgroundProcess()方法

1）Context容器的运行需要其他组件的支持，例如载入器和Session 管理器。通常来说，这些组件需要使用各自的线程执行一些后台处理程序；

2）为了节省资源，在tomcat5中，使用了不同的方法。所有的后台处理共享同一个线程。若某个组件或 servlet容器需要周期性地执行一个操作，只需要将代码写到其 backgroundProcess()方法中即可；（干货——tomcat5中，所有的后台处理共享同一个线程。）

3）这个共享线程在 ContainerBase对象中创建。ContainerBase.start()方法调用其 threadStart()方法启动该后台线程；（Attention-这是tomcat5中的 ContainerBase.start()）

public synchronized void start() throws LifecycleException { //org.apache.catalina.core.ContainerBase.start() in tomcat5.// Validate and update our current component stateif (started) {log.info(sm.getString("containerBase.alreadyStarted", logName()));return;}        // Notify our interested LifecycleListenerslifecycle.fireLifecycleEvent(BEFORE_START_EVENT, null);started = true;// Start our subordinate components, if anyif ((loader != null) && (loader instanceof Lifecycle))((Lifecycle) loader).start();getLogger();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 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);// Start our threadthreadStart(); //highlight line.// Notify our interested LifecycleListenerslifecycle.fireLifecycleEvent(AFTER_START_EVENT, null);}

protected void threadStart() { //org.apache.catalina.core.ContainerBase.threadStart() in tomcat5.if (thread != null)return;if (backgroundProcessorDelay <= 0)return;threadDone = false;String threadName = "ContainerBackgroundProcessor[" + toString() + "]";thread = new Thread(new ContainerBackgroundProcessor(), threadName); //highlight line.thread.setDaemon(true);thread.start();}

4）threadStart()方法：通过传入一个实现了 java.lang.Runnable接口的 ContainerBackgroundProcessor 类的实例构造一个新线程。其ContainerBackgroundProcessor定义如下：

protected class ContainerBackgroundProcessor implements Runnable { //org.apache.catalina.core.ContainerBase.ContainerBackroundProcessor class defined in tomcat 5, which is a inner class in ContainerBasepublic void run() {while (!threadDone) {try {Thread.sleep(backgroundProcessorDelay * 1000L);} catch (InterruptedException e) {;}if (!threadDone) {Container parent = (Container) getMappingObject();ClassLoader cl = Thread.currentThread().getContextClassLoader();if (parent.getLoader() != null) {cl = parent.getLoader().getClassLoader();}processChildren(parent, cl); // highlight line.}}}protected void processChildren(Container container, ClassLoader cl) {try {if (container.getLoader() != null) {Thread.currentThread().setContextClassLoader(container.getLoader().getClassLoader());}container.backgroundProcess(); // highlight line.} catch (Throwable t) {log.error("Exception invoking periodic operation: ", t);} finally {Thread.currentThread().setContextClassLoader(cl);}Container[] children = container.findChildren();for (int i = 0; i < children.length; i++) {if (children[i].getBackgroundProcessorDelay() <= 0) {processChildren(children[i], cl);}}}}

对以上代码的分析（Analysis）：

A1）ContainerBackgroundProcessor 类：实际上是 ContainerBase类的内部类；

A2）在其run()方法中是一个while 循环，周期性地调用其 processChildren()方法：而processChildren()方法会调用其自身对象的 backgroundProcess()方法和其每个子容器的 processChildren()方法；

A3）通过实现backgroundProcess()方法，ContainerBase类的子类可以使用一个专用线程来执行周期性任务；

5）tomcat5 中 StandardContext.backgroundProcess()方法的实现如下：

public void backgroundProcess() { //org.apache.catalina.core.ContainerBase.backgroundProcess() in tomcat 5.if (!started)return;if (cluster != null) {try {cluster.backgroundProcess();} catch (Exception e) {log.warn(sm.getString("containerBase.backgroundProcess.cluster", cluster), e);                }}if (loader != null) {try {loader.backgroundProcess();} catch (Exception e) {log.warn(sm.getString("containerBase.backgroundProcess.loader", loader), e);                }}if (manager != null) {try {manager.backgroundProcess();} catch (Exception e) {log.warn(sm.getString("containerBase.backgroundProcess.manager", manager), e);                }}if (realm != null) {try {realm.backgroundProcess();} catch (Exception e) {log.warn(sm.getString("containerBase.backgroundProcess.realm", realm), e);                }}Valve current = pipeline.getFirst();while (current != null) {try {current.backgroundProcess();} catch (Exception e) {log.warn(sm.getString("containerBase.backgroundProcess.valve", current), e);                }current = current.getNext();}lifecycle.fireLifecycleEvent(Lifecycle.PERIODIC_EVENT, null);}