tomcat源码：Context容器和Wrapper容器
来源：互联网 发布：集思宝安卓软件 编辑：程序博客网 时间：2024/05/16 19:46
Context容器是一个Web项目的代表，主要管理Servlet实例，在Tomcat中Servlet实例是以Wrapper出现的，现在问题是如何才能通过Context容器找到具体的Servlet呢？在解决这个问题之前，Context容器需要先启动，启动的过程就是加载个类资源文件以及打开子容器以及Pipeline管道的过程。启动Context容器后，就可以处理具体的请求了，具体是通过Request对象，从代码清单4-3的Wrapper wrapper = request.getWrapper()就可以看出来。
那么Context调用invoke方法后又发生什么了呢？具体执行的是org.apache.catalina.core.StandardContextValve的invoke方法。相当于进入了Context管道中，要开始通过管道中一个个闸门了。
StandardContext的处理流程可以用下面的图简化：
代码清单4-3：
/** * Select the appropriate child Wrapper to process this request, * based on the specified request URI. If no matching Wrapper can * be found, return an appropriate HTTP error. * * @param request Request to be processed * @param response Response to be produced * * @exception IOException if an input/output error occurred * @exception ServletException if a servlet error occurred */@Overridepublic final void invoke(Request request, Response response) throws IOException, ServletException { // Disallow any direct access to resources under WEB-INF or META-INF MessageBytes requestPathMB = request.getRequestPathMB(); if ((requestPathMB.startsWithIgnoreCase("/META-INF/", 0)) || (requestPathMB.equalsIgnoreCase("/META-INF")) || (requestPathMB.startsWithIgnoreCase("/WEB-INF/", 0)) || (requestPathMB.equalsIgnoreCase("/WEB-INF"))) { response.sendError(HttpServletResponse.SC_NOT_FOUND); return; } // Select the Wrapper to be used for this Request Wrapper wrapper = request.getWrapper(); if (wrapper == null || wrapper.isUnavailable()) { response.sendError(HttpServletResponse.SC_NOT_FOUND); return; } // Acknowledge the request try { response.sendAcknowledgement(); } catch (IOException ioe) { container.getLogger().error(sm.getString( "standardContextValve.acknowledgeException"), ioe); request.setAttribute(RequestDispatcher.ERROR_EXCEPTION, ioe); response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR); return; } if (request.isAsyncSupported()) { request.setAsyncSupported(wrapper.getPipeline().isAsyncSupported()); } wrapper.getPipeline().getFirst().invoke(request, response);}- 禁止直接访问WEB-INF或者META-INF目录下的资源
- 选择具体的Wrapper处理请求
- 返回一个确认响应
- 调用Wrapper容器的invoke方法，把处理请求交给StandardWrapperValve处理
Wrapper容器
Wrapper容器负责管理一个Servlet，包括Servlet的装载、初始化、资源回收。Wrapper是最底层的容器，其不能在添加子容器了。Wrapper是一个接口，其标准实现类是StandardWrapper，下面是这两个类的结构：
上面的图都只是类的一部分，由于Wrapper与Servlet息息相关，其中的loadServlet方法负责装载Servlet，其源码如下：
代码清单4-4：
/** * Load and initialize an instance of this servlet, if there is not already * at least one initialized instance. This can be used, for example, to * load servlets that are marked in the deployment descriptor to be loaded * at server startup time. */public synchronized Servlet loadServlet() throws ServletException { if (unloading) { throw new ServletException( sm.getString("standardWrapper.unloading", getName())); } // Nothing to do if we already have an instance or an instance pool if (!singleThreadModel && (instance != null)) return instance; PrintStream out = System.out; if (swallowOutput) { SystemLogHandler.startCapture(); } Servlet servlet; try { long t1=System.currentTimeMillis(); // Complain if no servlet class has been specified if (servletClass == null) { unavailable(null); throw new ServletException (sm.getString("standardWrapper.notClass", getName())); } InstanceManager instanceManager = ((StandardContext)getParent()).getInstanceManager(); try { servlet = (Servlet) instanceManager.newInstance(servletClass); } catch (ClassCastException e) { unavailable(null); // Restore the context ClassLoader throw new ServletException (sm.getString("standardWrapper.notServlet", servletClass), e); } catch (Throwable e) { e = ExceptionUtils.unwrapInvocationTargetException(e); ExceptionUtils.handleThrowable(e); unavailable(null); // Added extra log statement for Bugzilla 36630: // http://issues.apache.org/bugzilla/show_bug.cgi?id=36630 if(log.isDebugEnabled()) { log.debug(sm.getString("standardWrapper.instantiate", servletClass), e); } // Restore the context ClassLoader throw new ServletException (sm.getString("standardWrapper.instantiate", servletClass), e); } if (multipartConfigElement == null) { MultipartConfig annotation = servlet.getClass().getAnnotation(MultipartConfig.class); if (annotation != null) { multipartConfigElement = new MultipartConfigElement(annotation); } } processServletSecurityAnnotation(servlet.getClass()); // Special handling for ContainerServlet instances if ((servlet instanceof ContainerServlet) && (isContainerProvidedServlet(servletClass) || ((Context) getParent()).getPrivileged() )) { ((ContainerServlet) servlet).setWrapper(this); } classLoadTime=(int) (System.currentTimeMillis() -t1); if (servlet instanceof SingleThreadModel) { if (instancePool == null) { instancePool = new Stack<Servlet>(); } singleThreadModel = true; } //init servlet instance initServlet(servlet); fireContainerEvent("load", this); loadTime=System.currentTimeMillis() -t1; } finally { if (swallowOutput) { String log = SystemLogHandler.stopCapture(); if (log != null && log.length() > 0) { if (getServletContext() != null) { getServletContext().log(log); } else { out.println(log); } } } } return servlet;}该类主要负责初始化一个Servlet实例，并调用该实例的init方法，然后通知感兴趣的事件监听程序。代码清单4-3中调用了Wrapper的invoke方法，这个方法完成什么呢？
代码清单4-5：
/** * Invoke the servlet we are managing, respecting the rules regarding * servlet lifecycle and SingleThreadModel support. * * @param request Request to be processed * @param response Response to be produced * * @exception IOException if an input/output error occurred * @exception ServletException if a servlet error occurred */@Overridepublic final void invoke(Request request, Response response) throws IOException, ServletException { // Initialize local variables we may need boolean unavailable = false; Throwable throwable = null; // This should be a Request attribute... long t1=System.currentTimeMillis(); requestCount++; StandardWrapper wrapper = (StandardWrapper) getContainer(); Servlet servlet = null; Context context = (Context) wrapper.getParent(); // Check for the application being marked unavailable if (!context.getState().isAvailable()) { response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE, sm.getString("standardContext.isUnavailable")); unavailable = true; } // Check for the servlet being marked unavailable 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; } // Allocate a servlet instance to process this request try { if (!unavailable) { 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); } catch (Throwable e) { ExceptionUtils.handleThrowable(e); container.getLogger().error(sm.getString("standardWrapper.allocateException", wrapper.getName()), e); throwable = e; exception(request, response, e); servlet = null; } // Identify if the request is Comet related now that the servlet has been allocated boolean comet = false; if (servlet instanceof CometProcessor && request.getAttribute( Globals.COMET_SUPPORTED_ATTR) == Boolean.TRUE) { comet = true; request.setComet(true); } MessageBytes requestPathMB = request.getRequestPathMB(); DispatcherType dispatcherType = DispatcherType.REQUEST; if (request.getDispatcherType()==DispatcherType.ASYNC) dispatcherType = DispatcherType.ASYNC; request.setAttribute(Globals.DISPATCHER_TYPE_ATTR,dispatcherType); request.setAttribute(Globals.DISPATCHER_REQUEST_PATH_ATTR, requestPathMB); // Create the filter chain for this request ApplicationFilterFactory factory = ApplicationFilterFactory.getInstance(); ApplicationFilterChain filterChain = factory.createFilterChain(request, wrapper, servlet); // Reset comet flag value after creating the filter chain request.setComet(false); // Call the filter chain for this request // NOTE: This also calls the servlet's service() method try { if ((servlet != null) && (filterChain != null)) { // Swallow output if needed if (context.getSwallowOutput()) { try { SystemLogHandler.startCapture(); if (request.isAsyncDispatching()) { //TODO SERVLET3 - async ((AsyncContextImpl)request.getAsyncContext()).doInternalDispatch(); } else 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 (request.isAsyncDispatching()) { //TODO SERVLET3 - async ((AsyncContextImpl)request.getAsyncContext()).doInternalDispatch(); } else if (comet) { request.setComet(true); filterChain.doFilterEvent(request.getEvent()); } else { filterChain.doFilter (request.getRequest(), response.getResponse()); } } } } catch (ClientAbortException e) { throwable = e; exception(request, response, e); } catch (IOException e) { container.getLogger().error(sm.getString( "standardWrapper.serviceException", wrapper.getName(), context.getName()), e); throwable = e; exception(request, response, e); } catch (UnavailableException e) { container.getLogger().error(sm.getString( "standardWrapper.serviceException", wrapper.getName(), context.getName()), e); // throwable = e; // exception(request, response, 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())); } // Do not save exception in 'throwable', because we // do not want to do exception(request, response, e) processing } catch (ServletException e) { Throwable rootCause = StandardWrapper.getRootCause(e); if (!(rootCause instanceof ClientAbortException)) { container.getLogger().error(sm.getString( "standardWrapper.serviceExceptionRoot", wrapper.getName(), context.getName(), e.getMessage()), rootCause); } throwable = e; exception(request, response, e); } catch (Throwable e) { ExceptionUtils.handleThrowable(e); container.getLogger().error(sm.getString( "standardWrapper.serviceException", wrapper.getName(), context.getName()), e); throwable = e; exception(request, response, e); } // Release the filter chain (if any) for this request if (filterChain != null) { if (request.isComet()) { // If this is a Comet request, then the same chain will be used for the // processing of all subsequent events. filterChain.reuse(); } else { filterChain.release(); } } // Deallocate the allocated servlet instance try { if (servlet != null) { wrapper.deallocate(servlet); } } catch (Throwable e) { ExceptionUtils.handleThrowable(e); container.getLogger().error(sm.getString("standardWrapper.deallocateException", wrapper.getName()), e); if (throwable == null) { throwable = e; exception(request, response, e); } } // If this servlet has been marked permanently unavailable, // unload it and release this instance try { if ((servlet != null) && (wrapper.getAvailable() == Long.MAX_VALUE)) { wrapper.unload(); } } catch (Throwable e) { ExceptionUtils.handleThrowable(e); container.getLogger().error(sm.getString("standardWrapper.unloadException", wrapper.getName()), e); if (throwable == null) { throwable = e; exception(request, response, e); } }}- 初始化一些本地变量
- 判断当前应用是否可用，就是判断是否确实有这个项目
- 分配一个Servlet实例
- 为请求创建一个过滤器链
- 过滤器过滤请求
- 关闭过滤器
- 重新委派原来委派的Servlet实例
- 释放资源
这个方法与上面的loadServlet关系如下：
可以看出在调用loadServlet的allocate方法的时候调用了StandardWrapperValve的invoke方法，在Wrapper容器获得请求后，通过allocate方法从实例池栈中弹出一个servlet实例来处理这个请求，servlet实例被封装成filterChain对象，紧接着通过一系列的过滤器过滤到达servlet.service()方法。这个过程可以如下：
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