Tomcat源码剖析之Pipeline-Valve

先分析它的处理模式
Pipe-Value是责任链模式
责任链模式是指在一个请求处理的过程中有多个处理者依次对请求进行处理
Pipe-Value的管道模型和普通的责任链模型区别

每个pipeline都有特定的value,而且在管道的最后执行，BaseValue不可删除
上层的管道的value会调用下层的

4个容器有四个basevalve

在Filter中用到的FilterChain其实就是这种模式

PIpevalve的处理流程图

Pipeline管道实现分为生命周期管理和实现请求······、
Pipeline生命周期实现部分主要依托于ContainerBase的实现

 protected synchronized void startInternal() throws LifecycleException {
        //。。。。。
        //调用管道启动的方法
        // Start the Valves in our pipeline (including the basic), if any
        if (pipeline instanceof Lifecycle)
            ((Lifecycle) pipeline).start();
         //是不是很熟悉   
    }

他们的stopinternal 和destroyinternal也是循环调用stop 和destroy
因为Container的四个子容器都继承自Containnerbase所以他们在执行生命周期方法时也会调用管道相应的生命周期方法。
Pipeline类型是StandardPipeline类型 里面的额valve保存在first属性里 valve是链式结构 ，basevalve单独保存在basic中而且不可为空，
然后看一下StandardPipeLine的生命周期的处理方式
里面有个方法是否异步支持

@Override
    protected void initInternal() {
        // NOOP
    }

什么也没做

  protected synchronized void startInternal() throws LifecycleException {

        // Start the Valves in our pipeline (including the basic), if any
        Valve current = first;
        if (current == null) {
            current = basic;
        }
        while (current != null) {
            if (current instanceof Lifecycle)
                ((Lifecycle) current).start();
            current = current.getNext();
        }

        setState(LifecycleState.STARTING);
    }

遍历链表调用每个valve的start方法，如果为空则采用basic,然后设置状态

protected synchronized void stopInternal() throws LifecycleException {

        setState(LifecycleState.STOPPING);

        // Stop the Valves in our pipeline (including the basic), if any
        Valve current = first;
        if (current == null) {
            current = basic;
        }
        while (current != null) {
            if (current instanceof Lifecycle)
                ((Lifecycle) current).stop();
            current = current.getNext();
        }
    }

遍历链表调用stop方法

 protected void destroyInternal() {
        Valve[] valves = getValves();
        for (Valve valve : valves) {
            removeValve(valve);
        }
    }

不明白这里为变成了数组形式
删除所有valve,只不过是在getValves他把链表转化为了数组而已。方法设计的巧妙逻辑清晰感觉复杂

 public Valve[] getValves() {

        ArrayList<Valve> valveList = new ArrayList<Valve>();
        Valve current = first;
        if (current == null) {
            current = basic;
        }
        while (current != null) {
            valveList.add(current);
            current = current.getNext();
        }

        return valveList.toArray(new Valve[0]);

    }

把valve链表转为数组包括null的处理。

第二部分Pipeline管道处理请求实现的部分
基础：
Pipeline调用了所包含Valve的invoke方法处理请求 并且在basevalve里调用了子容器的所包含的valve的invoke方法，直到最后调用了wrapper的pipeline所包含的basevalve。
先分析一下顶层的pipeline会最后使用到standardEngineValve
ValveBase实现了Valve接口和Contained接口和LifecyleMBeans
并且提供了部分默认实现。

final class StandardEngineValve
    extends ValveBase {
    //------------------------------------------------------ Constructor
    public StandardEngineValve() {
        super(true);
    }

    private static final String info =
        "org.apache.catalina.core.StandardEngineValve/1.0";

    private static final StringManager sm =
        StringManager.getManager(Constants.Package);


    // ------------------------------------- Properties
    public String getInfo() {

        return (info);

    }


    // ------------------------------------- Public Methods


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

        // Select the Host to be used for this Request
        Host host = request.getHost();
        if (host == null) {
            response.sendError
                (HttpServletResponse.SC_BAD_REQUEST,
                 sm.getString("standardEngine.noHost", 
                              request.getServerName()));
            return;
        }
        if (request.isAsyncSupported()) {
            request.setAsyncSupported(host.getPipeline().isAsyncSupported());
        }

        // Ask this Host to process this request
        host.getPipeline().getFirst().invoke(request, response);

    }

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

        // Ask this Host to process this request
        request.getHost().getPipeline().getFirst().event(request, response, event);

    }

}

我么感兴趣的起始是两个方法
invoke方法

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

        // Select the Host to be used for this Request
        Host host = request.getHost();
        if (host == null) {
            response.sendError
                (HttpServletResponse.SC_BAD_REQUEST,
                 sm.getString("standardEngine.noHost", 
                              request.getServerName()));
            return;
        }
        if (request.isAsyncSupported()) {
            request.setAsyncSupported(host.getPipeline().isAsyncSupported());
        }

        // Ask this Host to process this request
        host.getPipeline().getFirst().invoke(request, response);

    }

它的实现非常简单首先从request中获取到Host，然后调用其管道的第一个Valve的invoke方法去处理。
同样可推到Host调用Context的basevalve的
Context调用Wrapper的
而对于Wrapper的来说我们就比较感兴趣了。

public 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.incrementAndGet();
        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 && Boolean.TRUE.equals(request.getAttribute(
                Globals.COMET_SUPPORTED_ATTR))) {
            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()) {
                            request.getAsyncContextInternal().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()) {
                        request.getAsyncContextInternal().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);
            }
        }
        long t2=System.currentTimeMillis();

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

    }

是不是很惊喜 是不是很长。既然那么长那就不看了
原理呢是
Valve创建FilterChain并调用其doFilter方法来处理请求

FilterChain包含了我们配置与请求的匹配的Filter和Servlet，它的doFilter会依次调用所有的Filter的doFilter方法和Servlet的service方法。这样请求就得到了处理。

总结来说Filter和Servlet的实际处理请求的方法是在wrapper的管道pipeline的Basevalve StandardWrapperValve中调用，生命周期的相关方法Wrapper的实现类StandardWrapper中调用。

虽然分析完了 但为什么这样做 还是有点不明白。。。。

下一节分析另一个组件Connector。