Tomcat请求处理(五) -- 请求在容器间的流动

请求在Tomcat中传到了CoyoteAdapter的#service()方法中后，就要准备进入Pipeline了，如#service()方法中的这句所示：
connector.getContainer().getPipeline().getFirst().invoke(request, response);

这里的Container是Engine，然后得到它的Pipeline对象，然后得到他的第一个Valve，如果没有配置的话第一个Valve就是Basic的了，这里就是org.apache.catalina.core.StandardEngineValve，最后调用了它的#invoke()方法，源代码如下所示：

	public final void invoke(Request request, Response response) throws IOException,
			ServletException {

		// 获得Host对象
		Host host = request.getHost();
		if (host == null) {
			response.sendError(HttpServletResponse.SC_BAD_REQUEST, sm.getString(
					"standardEngine.noHost", request.getServerName()));
			return;
		}

		// 将请求传递给Host
		host.getPipeline().getFirst().invoke(request, response);

	}

这个Valve并没做什么实质性的东西，只是将请求继续传递，当然可以定义自己的Valve实现一些特殊的行为。
还是来继续请求的处理过程，和上边Engine的情况类似，请求这次到了org.apache.catalina.core.StandardHostValve的#invoke()方法，源代码如下所示：

	public final void invoke(Request request, Response response) throws IOException,
			ServletException {

		// 获得Context对象
		Context context = request.getContext();
		if (context == null) {
			response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, sm
					.getString("standardHost.noContext"));
			return;
		}

		// 如果没有设置Loader，那么设置为context自己的ClassLoader
		if (context.getLoader() != null) {
			Thread.currentThread().setContextClassLoader(context.getLoader().getClassLoader());
		}

		// 将请求通过Pipeline给Context
		context.getPipeline().getFirst().invoke(request, response);

		if (Globals.STRICT_SERVLET_COMPLIANCE) {
			request.getSession(false);
		}

		// 处理错误页
		response.setSuspended(false);

		Throwable t = (Throwable) request.getAttribute(Globals.EXCEPTION_ATTR);

		if (t != null) {
			throwable(request, response, t);
		} else {
			status(request, response);
		}

		// 恢复ClassLoader
		Thread.currentThread().setContextClassLoader(StandardHostValve.class.getClassLoader());

	}

不出意外的，请求下边就到了org.apache.catalina.core.StandardContextValve，源代码如下：

	public final void invoke(Request request, Response response) throws IOException,
			ServletException {

		// 不允许请求访问META-INF和WEB-INF文件夹下的内容。
		MessageBytes requestPathMB = request.getRequestPathMB();
		if ((requestPathMB.startsWithIgnoreCase("/META-INF/", 0))
				|| (requestPathMB.equalsIgnoreCase("/META-INF"))
				|| (requestPathMB.startsWithIgnoreCase("/WEB-INF/", 0))
				|| (requestPathMB.equalsIgnoreCase("/WEB-INF"))) {
			notFound(response);
			return;
		}

		// 如果系统正在重新载入中，那么暂停请求。
		boolean reloaded = false;
		while (context.getPaused()) {
			reloaded = true;
			try {
				Thread.sleep(1000);
			} catch (InterruptedException e) {
				;
			}
		}

		// 如果正在重载，停止老的WebappClassLoader并创建一个新的
		if (reloaded && context.getLoader() != null && context.getLoader().getClassLoader() != null) {
			Thread.currentThread().setContextClassLoader(context.getLoader().getClassLoader());
		}

		// 获得Wrapper对象
		Wrapper wrapper = request.getWrapper();
		if (wrapper == null) {
			notFound(response);
			return;
		} else if (wrapper.isUnavailable()) {
			wrapper = (Wrapper) container.findChild(wrapper.getName());
			if (wrapper == null) {
				notFound(response);
				return;
			}
		}

		// 获得Listener列表
		Object instances[] = context.getApplicationEventListeners();

		ServletRequestEvent event = null;

		if ((instances != null) && (instances.length > 0)) {
			event = new ServletRequestEvent(((StandardContext) container).getServletContext(),
					request.getRequest());

			for (int i = 0; i < instances.length; i++) {
				if (instances[i] == null)
					continue;
				if (!(instances[i] instanceof ServletRequestListener))
					continue;
				ServletRequestListener listener = (ServletRequestListener) instances[i];
				try {
					// 调用请求初始化事件
					listener.requestInitialized(event);
				} catch (Throwable t) {
					container.getLogger().error(
							sm.getString("standardContext.requestListener.requestInit",
									instances[i].getClass().getName()), t);
					ServletRequest sreq = request.getRequest();
					sreq.setAttribute(Globals.EXCEPTION_ATTR, t);
					return;
				}
			}
		}

		// 调用Wrapper的Valve
		wrapper.getPipeline().getFirst().invoke(request, response);

		if ((instances != null) && (instances.length > 0)) {
			for (int i = 0; i < instances.length; i++) {
				if (instances[i] == null)
					continue;
				if (!(instances[i] instanceof ServletRequestListener))
					continue;
				ServletRequestListener listener = (ServletRequestListener) instances[i];
				try {
					// 调用请求结束事件
					listener.requestDestroyed(event);
				} catch (Throwable t) {
					container.getLogger().error(
							sm.getString("standardContext.requestListener.requestDestroy",
									instances[i].getClass().getName()), t);
					ServletRequest sreq = request.getRequest();
					sreq.setAttribute(Globals.EXCEPTION_ATTR, t);
				}
			}
		}

	}

这个Valve重要的是包括了对Listener的调用，最后来看一下Wrapper的Valve调用(org.apache.catalina.core.StandardWrapperValve)。

public final void invoke(Request request, Response response) throws IOException,
			ServletException {

		boolean unavailable = false;
		Throwable throwable = null;

		long t1 = System.currentTimeMillis();
		requestCount++;
		// 获得Wrapper所关联的对象
		StandardWrapper wrapper = (StandardWrapper) getContainer();
		// Servlet对象
		Servlet servlet = null;
		// 获得Context对象
		Context context = (Context) wrapper.getParent();

		if (!context.getAvailable()) {
			response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE, sm
					.getString("standardContext.isUnavailable"));
			unavailable = true;
		}

		if (!unavailable && wrapper.isUnavailable()) {
			container.getLogger().info(
					sm.getString("standardWrapper.isUnavailable", wrapper.getName()));
			long available = wrapper.getAvailable();
			if ((available > 0L) && (available < Long.MAX_VALUE)) {
				response.setDateHeader("Retry-After", available);
				response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE, sm.getString(
						"standardWrapper.isUnavailable", wrapper.getName()));
			} else if (available == Long.MAX_VALUE) {
				response.sendError(HttpServletResponse.SC_NOT_FOUND, sm.getString(
						"standardWrapper.notFound", wrapper.getName()));
			}
			unavailable = true;
		}

		try {
			if (!unavailable) {
				// 分配一个Servelt实例
				servlet = wrapper.allocate();
			}
		} catch (UnavailableException e) {
			container.getLogger().error(
					sm.getString("standardWrapper.allocateException", wrapper.getName()), e);
			long available = wrapper.getAvailable();
			if ((available > 0L) && (available < Long.MAX_VALUE)) {
				response.setDateHeader("Retry-After", available);
				response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE, sm.getString(
						"standardWrapper.isUnavailable", wrapper.getName()));
			} else if (available == Long.MAX_VALUE) {
				response.sendError(HttpServletResponse.SC_NOT_FOUND, sm.getString(
						"standardWrapper.notFound", wrapper.getName()));
			}
		} catch (ServletException e) {
			container.getLogger().error(
					sm.getString("standardWrapper.allocateException", wrapper.getName()),
					StandardWrapper.getRootCause(e));
			throwable = e;
			exception(request, response, e);
			servlet = null;
		} catch (Throwable e) {
			container.getLogger().error(
					sm.getString("standardWrapper.allocateException", wrapper.getName()), e);
			throwable = e;
			exception(request, response, e);
			servlet = null;
		}

		boolean comet = false;
		if (servlet instanceof CometProcessor
				&& request.getAttribute("org.apache.tomcat.comet.support") == Boolean.TRUE) {
			comet = true;
			request.setComet(true);
		}

		// 告知Request已经收到
		try {
			response.sendAcknowledgement();
		} catch (IOException e) {
			request.removeAttribute(Globals.JSP_FILE_ATTR);
			container.getLogger().warn(
					sm.getString("standardWrapper.acknowledgeException", wrapper.getName()), e);
			throwable = e;
			exception(request, response, e);
		} catch (Throwable e) {
			container.getLogger().error(
					sm.getString("standardWrapper.acknowledgeException", wrapper.getName()), e);
			throwable = e;
			exception(request, response, e);
			servlet = null;
		}
		MessageBytes requestPathMB = null;
		if (request != null) {
			requestPathMB = request.getRequestPathMB();
		}
		
		request.setAttribute(ApplicationFilterFactory.DISPATCHER_TYPE_ATTR,
				ApplicationFilterFactory.REQUEST_INTEGER);
		request.setAttribute(ApplicationFilterFactory.DISPATCHER_REQUEST_PATH_ATTR, requestPathMB);
		// 创建FilterChain
		ApplicationFilterFactory factory = ApplicationFilterFactory.getInstance();
		ApplicationFilterChain filterChain = factory.createFilterChain(request, wrapper, servlet);

		request.setComet(false);

		try {
			// web.xml中的<jsp-file>标签
			String jspFile = wrapper.getJspFile();
			if (jspFile != null)
				request.setAttribute(Globals.JSP_FILE_ATTR, jspFile);
			else
				request.removeAttribute(Globals.JSP_FILE_ATTR);
			
			// 调用Filter
			if ((servlet != null) && (filterChain != null)) {
				if (context.getSwallowOutput()) {
					try {
						SystemLogHandler.startCapture();
						if (comet) {
							filterChain.doFilterEvent(request.getEvent());
							request.setComet(true);
						} else {
							filterChain.doFilter(request.getRequest(), response.getResponse());
						}
					} finally {
						String log = SystemLogHandler.stopCapture();
						if (log != null && log.length() > 0) {
							context.getLogger().info(log);
						}
					}
				} else {
					if (comet) {
						request.setComet(true);
						filterChain.doFilterEvent(request.getEvent());
					} else {
						filterChain.doFilter(request.getRequest(), response.getResponse());
					}
				}

			}
			request.removeAttribute(Globals.JSP_FILE_ATTR);
		} catch (ClientAbortException e) {
			request.removeAttribute(Globals.JSP_FILE_ATTR);
			throwable = e;
			exception(request, response, e);
		} catch (IOException e) {
			request.removeAttribute(Globals.JSP_FILE_ATTR);
			container.getLogger().error(
					sm.getString("standardWrapper.serviceException", wrapper.getName()), e);
			throwable = e;
			exception(request, response, e);
		} catch (UnavailableException e) {
			request.removeAttribute(Globals.JSP_FILE_ATTR);
			container.getLogger().error(
					sm.getString("standardWrapper.serviceException", wrapper.getName()), e);

			wrapper.unavailable(e);
			long available = wrapper.getAvailable();
			if ((available > 0L) && (available < Long.MAX_VALUE)) {
				response.setDateHeader("Retry-After", available);
				response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE, sm.getString(
						"standardWrapper.isUnavailable", wrapper.getName()));
			} else if (available == Long.MAX_VALUE) {
				response.sendError(HttpServletResponse.SC_NOT_FOUND, sm.getString(
						"standardWrapper.notFound", wrapper.getName()));
			}

		} catch (ServletException e) {
			request.removeAttribute(Globals.JSP_FILE_ATTR);
			Throwable rootCause = StandardWrapper.getRootCause(e);
			if (!(rootCause instanceof ClientAbortException)) {
				container.getLogger().error(
						sm.getString("standardWrapper.serviceException", wrapper.getName()),
						rootCause);
			}
			throwable = e;
			exception(request, response, e);
		} catch (Throwable e) {
			request.removeAttribute(Globals.JSP_FILE_ATTR);
			container.getLogger().error(
					sm.getString("standardWrapper.serviceException", wrapper.getName()), e);
			throwable = e;
			exception(request, response, e);
		}

		if (filterChain != null) {
			if (request.isComet()) {
				filterChain.reuse();
			} else {
				filterChain.release();
			}
		}

		// 释放Servlet对象
		try {
			if (servlet != null) {
				wrapper.deallocate(servlet);
			}
		} catch (Throwable e) {
			container.getLogger().error(
					sm.getString("standardWrapper.deallocateException", wrapper.getName()), e);
			if (throwable == null) {
				throwable = e;
				exception(request, response, e);
			}
		}

		try {
			if ((servlet != null) && (wrapper.getAvailable() == Long.MAX_VALUE)) {
				wrapper.unload();
			}
		} catch (Throwable e) {
			container.getLogger().error(
					sm.getString("standardWrapper.unloadException", wrapper.getName()), e);
			if (throwable == null) {
				throwable = e;
				exception(request, response, e);
			}
		}
		long t2 = System.currentTimeMillis();

		long time = t2 - t1;
		processingTime += time;
		if (time > maxTime)
			maxTime = time;
		if (time < minTime)
			minTime = time;

	}

这段代码的关键点是Servlet实例的构建(servlet = wrapper.allocate();)和Filter Chain的调用(filterChain.doFilter(request.getRequest(), response.getResponse());)，具体的还要进入方法内部去仔细看一下。comet方式以后再详细看。