tomcat 的 Pipeline 机制

一。server.xml

在每个容器对象里面都有一个pipeline，Pipeline就像是每个容器的逻辑总线。

    <Host name="localhost"  appBase="webapps"
            unpackWARs="true" autoDeploy="true"
            xmlValidation="false" xmlNamespaceAware="false">

        <!-- SingleSignOn valve, share authentication between web applications
             Documentation at: /docs/config/valve.html -->
        <!--
        <Valve className="org.apache.catalina.authenticator.SingleSignOn" />
        -->

        <!-- Access log processes all example.
             Documentation at: /docs/config/valve.html -->
        <!--
        <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"  
               prefix="localhost_access_log." suffix=".txt" pattern="common" resolveHosts="false"/>
        -->

      </Host>

二。源码追踪

1.Engine

    /**
     * Create a new StandardEngine component with the default basic Valve.
     */
    public StandardEngine() {

        super();
        pipeline.setBasic(new StandardEngineValve());
        /* Set the jmvRoute using the system property jvmRoute */
        try {
            setJvmRoute(System.getProperty("jvmRoute"));
        } catch(Exception ex) {
        }
        // By default, the engine will hold the reloading thread
        backgroundProcessorDelay = 10;

    }

2.Host

    /**
     * Create a new StandardHost component with the default basic Valve.
     */
    public StandardHost() {

        super();
        pipeline.setBasic(new StandardHostValve());

    }

3.Context

    /**
     * Create a new StandardContext component with the default basic Valve.
     */
    public StandardContext() {

        super();
        pipeline.setBasic(new StandardContextValve());
        broadcaster = new NotificationBroadcasterSupport();

    }

4.Wrapper

    /**
     * Create a new StandardWrapper component with the default basic Valve.
     */
    public StandardWrapper() {

        super();
        swValve=new StandardWrapperValve();
        pipeline.setBasic(swValve);
        broadcaster = new NotificationBroadcasterSupport();

        if (restrictedServlets == null) {
            restrictedServlets = new Properties();
            try {
                InputStream is = 
                    this.getClass().getClassLoader().getResourceAsStream
                        ("org/apache/catalina/core/RestrictedServlets.properties");
                if (is != null) {
                    restrictedServlets.load(is);
                } else {
                    log.error(sm.getString("standardWrapper.restrictedServletsResource"));
                }
            } catch (IOException e) {
                log.error(sm.getString("standardWrapper.restrictedServletsResource"), e);
            }
        }
        
    }

三。ContainerBase

把Pipeline接口的实现委托给成员变量pipeline

public abstract class ContainerBase
    implements Container, Lifecycle, Pipeline, MBeanRegistration, Serializable {

1.setBasic

    public void setBasic(Valve valve) {

        pipeline.setBasic(valve);

    }

2.invoke

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

        pipeline.getFirst().invoke(request, response);

    }

3.继承

四。StandardPipeline

1.setBasic

    public void setBasic(Valve valve) {

        // Change components if necessary
        Valve oldBasic = this.basic;
        if (oldBasic == valve)
            return;

        // Stop the old component if necessary
        if (oldBasic != null) {
            if (started && (oldBasic instanceof Lifecycle)) {
                try {
                    ((Lifecycle) oldBasic).stop();
                } catch (LifecycleException e) {
                    log.error("StandardPipeline.setBasic: stop", e);
                }
            }
            if (oldBasic instanceof Contained) {
                try {
                    ((Contained) oldBasic).setContainer(null);
                } catch (Throwable t) {
                    ;
                }
            }
        }

        // Start the new component if necessary
        if (valve == null)
            return;
        if (valve instanceof Contained) {
            ((Contained) valve).setContainer(this.container);
        }
        if (valve instanceof Lifecycle) {
            try {
                ((Lifecycle) valve).start();
            } catch (LifecycleException e) {
                log.error("StandardPipeline.setBasic: start", e);
                return;
            }
        }

        // Update the pipeline
        Valve current = first;
        while (current != null) {
            if (current.getNext() == oldBasic) {
                current.setNext(valve);
                break;
            }
            current = current.getNext();
        }
        
        this.basic = valve;

    }

1.addValve

    public void addValve(Valve valve) {
    
        // Validate that we can add this Valve
        if (valve instanceof Contained)
            ((Contained) valve).setContainer(this.container);

        // Start the new component if necessary
        if (started) {
            if (valve instanceof Lifecycle) {
                try {
                    ((Lifecycle) valve).start();
                } catch (LifecycleException e) {
                    log.error("StandardPipeline.addValve: start: ", e);
                }
            }
            // Register the newly added valve
            registerValve(valve);
        }

        // Add this Valve to the set associated with this Pipeline
        if (first == null) {
            first = valve;
            valve.setNext(basic);
        } else {
            Valve current = first;
            while (current != null) {
                if (current.getNext() == basic) {
                    current.setNext(valve);
                    valve.setNext(basic);
                    break;
                }
                current = current.getNext();
            }
        }

    }

六。public interface Pipeline

Interface describing a collection of Valves that should be executed in sequence when the invoke() method is invoked. It is required that

a Valve somewhere in the pipeline (usually the last one) must process the request and create the corresponding response, rather than

trying to pass the request on.

There is generally a single Pipeline instance associated with each Container. The container's normal request processing functionality is

generally encapsulated in a container-specific Valve, which should always be executed at the end of a pipeline. To facilitate this, the 

setBasic() method is provided to set the Valve instance that will always be executed last. Other Valves will be executed in the order

that they were added, before the basic Valve is executed.