[Tomcat源码系列]结构解析 2）生命期控制结构
一、生命期控制结构基础
Tomcat的生命期控制是一个两层的结构
1）Lifecycle(org.apache.catalina.Lifecycle)：
??? 在前一篇中看到的各组件(Service、Connector、Engine、Host、Context、Wrapper)都会实现这个接口，我们看看这个接口的定义
public interface Lifecycle {public static final String INIT_EVENT = "init";public static final String START_EVENT = "start";public static final String BEFORE_START_EVENT = "before_start";public static final String AFTER_START_EVENT = "after_start";public static final String STOP_EVENT = "stop";public static final String BEFORE_STOP_EVENT = "before_stop";public static final String AFTER_STOP_EVENT = "after_stop";public static final String DESTROY_EVENT = "destroy";public static final String PERIODIC_EVENT = "periodic";public void addLifecycleListener(LifecycleListener listener);public LifecycleListener[] findLifecycleListeners();public void removeLifecycleListener(LifecycleListener listener);public void start() throws LifecycleException;public void stop() throws LifecycleException;}?2）LifecycleListener (org.apache.catalina.LifecycleListener)：
??? 在我们上一篇看到HostConfig就是输入LifecycleListener。
如下是LifecycleLister的定义
public interface LifecycleListener {public void lifecycleEvent(LifecycleEvent event);}?
二、Tomcat初始化处理过程
1.下面是上一个范例中涉及到的处理器初始化主要过程，可以看出来，通过类似的结构，实现了层层的初始化过程
非常简单明了，初始化自己、注册JMX、super.start三步骤，我们进入下一步
2）ContainerBase.start
public synchronized void start() throws LifecycleException { // Validate and update our current component state if (started) { if(log.isInfoEnabled()) log.info(sm.getString("containerBase.alreadyStarted", logName())); return; } // Notify our interested LifecycleListeners lifecycle.fireLifecycleEvent(BEFORE_START_EVENT, null); started = true; // Start our subordinate components, if any if ((loader != null) && (loader instanceof Lifecycle)) ((Lifecycle) loader).start(); logger = null; 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 any Container 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 any if (pipeline instanceof Lifecycle) ((Lifecycle) pipeline).start(); // Notify our interested LifecycleListeners lifecycle.fireLifecycleEvent(START_EVENT, null); // Start our thread threadStart(); // Notify our interested LifecycleListeners lifecycle.fireLifecycleEvent(AFTER_START_EVENT, null); }?如我们上面所说，也是几个简单的过程：触发初始化事件、初始化各组件、初始化children(层次间的关系通过children实现)。注意，ContainerBase本身会继承Lifecycle接口和Container接口，而StandardEngine、StandardHost、StandardContext、StandardWrapper都继承自ContainerBase，因此初始化方式非常类似。
3)HostConfig，HostConfig是一个LifecycleListener，如我们上一篇的DEMO代码，作为LifecycleListener注册到StandardHost中，在ContainerBase初始化开始阶段，会触发一个BEFORE_START_EVENT，触发HostConfig的初始化，HostConfig初始化过程是：HostConfig. lifecycleEvent-->HostConfig.start-->HostConfig. deployApps，我们看看HostConfig. deployApps是如何实现的
protected void deployApps() { File appBase = appBase(); File configBase = configBase(); // Deploy XML descriptors from configBase deployDescriptors(configBase, configBase.list()); // Deploy WARs, and loop if additional descriptors are found deployWARs(appBase, appBase.list()); // Deploy expanded folders deployDirectories(appBase, appBase.list()); }可以看到，是3种类型，分别是{tomcat}/conf/{hostname}/目录下的{context.xml}、{tomcat}/{appBase}/下的war和{tomcat}/{appBase}下的目录。我们再看看HostConfig. deployDirectory是如何实现的
protected void deployDirectory(String contextPath, File dir, String file) { DeployedApplication deployedApp = new DeployedApplication(contextPath); if (deploymentExists(contextPath)) return; // Deploy the application in this directory if( log.isDebugEnabled() ) log.debug(sm.getString("hostConfig.deployDir", file)); try { Context context = (Context) Class.forName(contextClass).newInstance(); if (context instanceof Lifecycle) { Class clazz = Class.forName(host.getConfigClass()); LifecycleListener listener = (LifecycleListener) clazz.newInstance(); ((Lifecycle) context).addLifecycleListener(listener); } context.setPath(contextPath); context.setDocBase(file); File configFile = new File(dir, Constants.ApplicationContextXml); if (deployXML) { context.setConfigFile(configFile.getAbsolutePath()); } host.addChild(context); deployedApp.redeployResources.put(dir.getAbsolutePath(), new Long(dir.lastModified())); if (deployXML) { deployedApp.redeployResources.put(configFile.getAbsolutePath(), new Long(configFile.lastModified())); } addWatchedResources(deployedApp, dir.getAbsolutePath(), context); } catch (Throwable t) { log.error(sm.getString("hostConfig.deployDir.error", file), t); } deployed.put(contextPath, deployedApp); }实际上也没有太多复杂的东西，需要更细节的了解可以看org.apache.catalina.startup.HostConfig的代码
4)ContextConfig，与HostConfig类似，我们这里直接进入ContextConfig.start
protected synchronized void start() { ...略 // Set properties based on DefaultContext Container container = context.getParent(); ...略 // Process the default and application web.xml files defaultWebConfig(); applicationWebConfig(); if (!context.getIgnoreAnnotations()) { applicationAnnotationsConfig(); } if (ok) { validateSecurityRoles(); } // Configure an authenticator if we need one if (ok) authenticatorConfig(); ...略 }其中defaultWebConfig解析{tomcat}/config/web.xml（提供JSP和welcome file的支持），而applicationWebConfig当然是每个应用的WEB-INF/web.xml了。解析的全过程不再细节描述，可以参见org.apache.catalina.startup.ContextConfig
5)在初始化过程当中，向Container(Engine、Host、Context、Config)注册child(addChild方法)的过程是需要重点关注的地方，由于跟后续请求处理的过程相关联，因此放在后面再做解析
三、通过如上层层初始化，我们的StandardEngine创建完毕，一切准备就绪，可以等待请求接入