Host和Engine容器
Context容器的父容器通常是Host容器。
Engine容器表示Catalina的整个servlet引擎。如果使用Engine容器，那么它总是处于容器层级的最顶层。默认情况下，Tomcat会使用Engine容器，并且有一个Host容器作为子容器。
Host接口继承Container接口
public interface Host extends Container {
...
}
StandardHost类继承ContainerBase并且实现Host接口，与StandardContext和StandardWrapper类相似，StandardHost类会在构造方法会设置一个基础阀门添加到管道中。
public StandardHost() {
super();
pipeline.setBasic(new StandardHostValve());
}
StandardHostValve类也和StandardContext，StandardWrapper相似，实现了一个invoke方法，基于具体的请求路径，选择合适的子容器处理请求，如果没有匹配的，则返回Http error。
public final void invoke(Request request, Response response)
throws IOException, ServletException { // Select the Context to be used for this Request
Context context = request.getContext();
if (context == null) {
response.sendError
(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
sm.getString("standardHost.noContext"));
return;
} // Bind the context CL to the current thread
if( context.getLoader() != null ) {
// Not started - it should check for availability first
// This should eventually move to Engine, it's generic.
if (Globals.IS_SECURITY_ENABLED) {
PrivilegedAction<Void> pa = new PrivilegedSetTccl(
context.getLoader().getClassLoader());
AccessController.doPrivileged(pa);
} else {
Thread.currentThread().setContextClassLoader
(context.getLoader().getClassLoader());
}
}
if (request.isAsyncSupported()) {
request.setAsyncSupported(context.getPipeline().isAsyncSupported());
} boolean asyncAtStart = request.isAsync();
boolean asyncDispatching = request.isAsyncDispatching();
if (asyncAtStart || context.fireRequestInitEvent(request)) { // Ask this Context to process this request. Requests that are in
// async mode and are not being dispatched to this resource must be
// in error and have been routed here to check for application
// defined error pages.
try {
if (!asyncAtStart || asyncDispatching) {
context.getPipeline().getFirst().invoke(request, response);
} else {
// Make sure this request/response is here because an error
// report is required.
if (!response.isErrorReportRequired()) {
throw new IllegalStateException(sm.getString("standardHost.asyncStateError"));
}
}
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
// If a new error occurred while trying to report a previous
// error simply log the new error and allow the original error
// to be reported.
if (response.isErrorReportRequired()) {
container.getLogger().error("Exception Processing " +
request.getRequestURI(), t);
} else {
request.setAttribute(RequestDispatcher.ERROR_EXCEPTION, t);
throwable(request, response, t);
}
} // Now that the request/response pair is back under container
// control lift the suspension so that the error handling can
// complete and/or the container can flush any remaining data
response.setSuspended(false); Throwable t = (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION); // Protect against NPEs if the context was destroyed during a
// long running request.
if (!context.getState().isAvailable()) {
return;
} // Look for (and render if found) an application level error page
if (response.isErrorReportRequired()) {
if (t != null) {
throwable(request, response, t);
} else {
status(request, response);
}
} if (!request.isAsync() && (!asyncAtStart || !response.isErrorReportRequired())) {
context.fireRequestDestroyEvent(request);
}
} // Access a session (if present) to update last accessed time, based on a
// strict interpretation of the specification
if (ACCESS_SESSION) {
request.getSession(false);
} // Restore the context classloader
if (Globals.IS_SECURITY_ENABLED) {
PrivilegedAction<Void> pa = new PrivilegedSetTccl(
StandardHostValve.class.getClassLoader());
AccessController.doPrivileged(pa);
} else {
Thread.currentThread().setContextClassLoader
(StandardHostValve.class.getClassLoader());
}
}
ContextConfig类
主要加载一些配置属性
web.xml的加载
/**
* Identify the application web.xml to be used and obtain an input source
* for it.
*/
protected InputSource getContextWebXmlSource() {
InputStream stream = null;
InputSource source = null;
URL url = null; String altDDName = null; // Open the application web.xml file, if it exists
ServletContext servletContext = context.getServletContext();
if (servletContext != null) {
altDDName = (String)servletContext.getAttribute(
Globals.ALT_DD_ATTR);
if (altDDName != null) {
try {
stream = new FileInputStream(altDDName);
url = new File(altDDName).toURI().toURL();
} catch (FileNotFoundException e) {
log.error(sm.getString("contextConfig.altDDNotFound",
altDDName));
} catch (MalformedURLException e) {
log.error(sm.getString("contextConfig.applicationUrl"));
}
}
else {
stream = servletContext.getResourceAsStream
(Constants.ApplicationWebXml);
try {
url = servletContext.getResource(
Constants.ApplicationWebXml);
} catch (MalformedURLException e) {
log.error(sm.getString("contextConfig.applicationUrl"));
}
}
}
if (stream == null || url == null) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("contextConfig.applicationMissing") + " " + context);
}
} else {
source = new InputSource(url.toExternalForm());
source.setByteStream(stream);
}
return source;
}
//常量类
public final class Constants{
...
public static final String ApplicationWebXml = "/WEB-INF/web.xml";
...
}