StandardContext
Context代表一个web应用，每个Context包含多个代表servlet的Wrapper，同时Context还需要加载器和管理器。
StandardContext配置
当StandardContext被构造以后，必须调用它的start方法，确保StandardContext为HTTP请求提供服务。如果start失败StandardContext的available属性将会被设置为false。
为了确保启动方法运行成功，需要做适当的配置。在Tomcat部署过程中，配置StandardContext过程中需要做很多事情，首先，必须确保StandardContext能读取%CATALINA_HOME%/conf目录下所有应用部署都要使用的默认web.xml文件；其次，也必须确保StandardContext实例能够处理应用级的web.xml，通常在其中有一些有效参数。
构造函数
public StandardContext() {
super();
pipeline.setBasic(new StandardContextValve());
namingResources.setContainer(this);
}
这里最重要的步骤是为管道pipeline添加StandardContextValue作为基础value，用来处理来自客户端的HTTP请求。
启动StandardContext
start方法初始化StandardContext，并告知监听则配置StandardContext实例，需要做如下事情：
1、 触发BEFORE_START事件；
2、 设置available属性值为false；
3、 设置configured属性值为false；
4、 设置resources；
5、 设置加载器；
6、 设置管理器；
7、 初始化字符集匹配器；
8、 启动其他分配给该Context的组件；
9、 启动子容器Wrapper；
10、 启动管道（pipeline）；
11、 启动管理器；
12、 触发START事件，这里监听器（ContextConfig）会执行配置操作，配置成功以后会把configred为true；
13、 检测configred值，如果为true，则做后面操作：调用postWelcomePages方法，加载需要在启动时候加载的wrapper，设置available为true；如果configred为false，则调用stop方法；
14、 触发AFTER_START事件。
start方法实现如下：
public synchronized void start() throws LifecycleException {
if (started)
throw new LifecycleException
(sm.getString("containerBase.alreadyStarted", logName()));
if (debug >= 1)
log("Starting");
// Notify our interested LifecycleListeners
lifecycle.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 necessary
if (getResources() == null) { // (1) Required by Loader
if (debug >= 1)
log("Configuring default Resources");
try {
if ((docBase != null) && (docBase.endsWith(".war")))
setResources(new WARDirContext());
else
setResources(new FileDirContext());
} catch (IllegalArgumentException e) {
log("Error initializing resources: " + e.getMessage());
ok = false;
}
}
if (ok && (resources instanceof ProxyDirContext)) {
DirContext dirContext =
((ProxyDirContext) resources).getDirContext();
if ((dirContext != null)
&& (dirContext instanceof BaseDirContext)) {
((BaseDirContext) dirContext).setDocBase(getBasePath());
((BaseDirContext) dirContext).allocate();
}
}
if (getLoader() == null) { // (2) Required by Manager
if (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 prerequisites
if (debug >= 1)
log("Configuring default Manager");
setManager(new StandardManager());
}
// Initialize character set mapper
getCharsetMapper();
// Post work directory
postWorkDirectory();
// Reading the "catalina.useNaming" environment variable
String 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 thread
ClassLoader oldCCL = bindThread();
// Standard container startup
if (debug >= 1)
log("Processing standard container startup");
if (ok) {
try {
addDefaultMapper(this.mapperClass);
started = true;
// Start our subordinate components, if any
if ((loader != null) && (loader instanceof Lifecycle))
((Lifecycle) loader).start();
if ((logger != null) && (logger instanceof Lifecycle))
((Lifecycle) logger).start();
// Unbinding thread
unbindThread(oldCCL);
// Binding thread
oldCCL = 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 any
Mapper mappers[] = findMappers();
for (int i = 0; i < mappers.length; i++) {
if (mappers[i] instanceof Lifecycle)
((Lifecycle) mappers[i]).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);
if ((manager != null) && (manager instanceof Lifecycle))
((Lifecycle) manager).start();
} finally {
// Unbinding thread
unbindThread(oldCCL);
}
}
if (!getConfigured())
ok = false;
// We put the resources into the servlet context
if (ok)
getServletContext().setAttribute
(Globals.RESOURCES_ATTR, getResources());
// Binding thread
oldCCL = bindThread();
// Create context attributes that will be required
if (ok) {
if (debug >= 1)
log("Posting standard context attributes");
postWelcomeFiles();
}
// Configure and call application event listeners and filters
if (ok) {
if (!listenerStart())
ok = false;
}
if (ok) {
if (!filterStart())
ok = false;
}
// Load and initialize all "load on startup" servlets
if (ok)
loadOnStartup(findChildren());
// Unbinding thread
unbindThread(oldCCL);
// Set available status depending upon startup success
if (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);
}
// Notify our interested LifecycleListeners
lifecycle.fireLifecycleEvent(AFTER_START_EVENT, null);
}
invoke方法
在Tomcat4中invoke方法被连接器调用，如果StandardContext是Host的子容器则被Host的invoke方法调用，在invoke方法中会检测是否重载应用，会等待应用重载完成，方法实现如下：
public void invoke(Request request, Response response)
throws IOException, ServletException {
// Wait if we are reloading
while (getPaused()) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
;
}
}
// Normal request processing
if (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);
}
}