【Tomcat9源码分析】Container、Pipeline和Vavle设计

转载请注明出处：http://blog.csdn.net/linxdcn/article/details/73800100

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1 概述

如果你对Tomcat的整个框架、组件、请求流程不熟悉，建议你先阅读以下3篇Tomcat概述性的文章，再来看本篇文章：

【Tomcat9源码分析】组件与框架概述
【Tomcat9源码分析】生命周期、启动、停止概述
【Tomcat9源码分析】请求过程概述

Container是Tomcat中很重要的容器，主要包含Engine、Host、Context和Wrapper，其采用了责任链的设计模式，来处理一次请求。

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2 Container分析

Container是一个接口，Tomcat提供了ContainerBase作为其实现的基类。

2.1 字段

public abstract class ContainerBase implements Container {    // 子容器    protected final HashMap<String, Container> children = new HashMap<>();    // 监听事件    protected final List<ContainerListener> listeners = new CopyOnWriteArrayList<>();    // Container对应的Pipeline    protected final Pipeline pipeline = new StandardPipeline(this);    // 领域对象    private volatile Realm realm = null;}

2.2 启动

public abstract class ContainerBase implements Container {    @Override    protected synchronized void startInternal() throws LifecycleException {        // 1 启动领域对象        Realm realm = getRealmInternal();        if (realm instanceof Lifecycle) {            ((Lifecycle) realm).start();        }        // 2 启动子容器        Container children[] = findChildren();        List<Future<Void>> results = new ArrayList<>();        for (int i = 0; i < children.length; i++) {            results.add(startStopExecutor.submit(new StartChild(children[i])));        }        // 3 启动Pipeline        if (pipeline instanceof Lifecycle)            ((Lifecycle) pipeline).start();        // 4 设置状态，启动本线程        setState(LifecycleState.STARTING);        threadStart();    }}

1. 启动领域对象
2. 启动子容器
3. 启动Pipeline
4. 设置状态，启动本线程

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3 Pipeline分析

Pipeline是一个接口，其实现类是StandardPipeline。

public class StandardPipeline extends LifecycleBase implements Pipeline {    // 基础阀门    protected Valve basic = null;    // 关联的容器    protected Container container = null;    // 第一个阀门    protected Valve first = null;    @Override    protected synchronized void startInternal() throws LifecycleException {        Valve current = first;        if (current == null) {            current = basic;        }        // 依次启动所有Value，Value是一个链表结构        while (current != null) {            if (current instanceof Lifecycle)                ((Lifecycle) current).start();            current = current.getNext();        }        setState(LifecycleState.STARTING);    }}

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4 Valve分析

Valve是一个接口，其基本实现的BaseValve类。

public abstract class ValveBase extends LifecycleMBeanBase implements Contained, Valve {    // 关联的Container    protected Container container = null;    // 下一个Valve    protected Valve next = null;    @Override    public Container getContainer() {        return container;    }    // 初始化    @Override    protected void initInternal() throws LifecycleException {        super.initInternal();        containerLog = getContainer().getLogger();    }    // 启动    @Override    protected synchronized void startInternal() throws LifecycleException {        setState(LifecycleState.STARTING);    }}

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5 几个重要的Valve

5.1 StandardEngineValve

final class StandardEngineValve extends ValveBase {    public final void invoke(Request request, Response response)        throws IOException, ServletException {        // 1 由request获取host        Host host = request.getHost();        if (host == null) {            // ...省略            return;        }        // 2 调用host的pipeline的vavle        host.getPipeline().getFirst().invoke(request, response);    }}

1. 根据request定位到可以处理的host对象
2. 依次调用host里的pipeline上的valve

5.2 StandardEngineValve

final class StandardHostValve extends ValveBase {    public final void invoke(Request request, Response response)        throws IOException, ServletException {        // 1 由request获取context        Context context = request.getContext();        try {            // 2 调用context里的pipeline上的valve            context.getPipeline().getFirst().invoke(request, response);            // response已经返回            response.setSuspended(false);            Throwable t = (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION);            // 3 如果有错误，重定向到错误页            if (response.isErrorReportRequired()) {                if (t != null) {                    throwable(request, response, t);                } else {                    status(request, response);                }            }        }     }}

1. 由request获取context
2. 调用context里的pipeline上的valve
3. 如果有错误，重定向到错误页

5.3 StandardContextValve

final class StandardContextValve extends ValveBase {    @Override    public final void invoke(Request request, Response response)        throws IOException, ServletException {        // 由request获取wrapper        Wrapper wrapper = request.getWrapper();        // ...省略        // 调用wrapper里的pipeline上的valve        wrapper.getPipeline().getFirst().invoke(request, response);    }}

1. 由request获取wrapper
2. 调用wrapper里的pipeline上的valve

5.4 StandardWrapperValve

final class StandardWrapperValve extends ValveBase {    public final void invoke(Request request, Response response)        throws IOException, ServletException {        // 1 获取wrapper, context        StandardWrapper wrapper = (StandardWrapper) getContainer();        Servlet servlet = null;        Context context = (Context) wrapper.getParent();        // 2 加载servlet        try {            if (!unavailable) {                servlet = wrapper.allocate();            }        } // ...省略catch        // 3 新建一个 filter 链表        ApplicationFilterChain filterChain =                ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);        // servlet会放在 filter 链表最后，并且最后会调用servlet的service方法        try {            if ((servlet != null) && (filterChain != null)) {                // Swallow output if needed                if (context.getSwallowOutput()) {                    // 4 调用 filter 链表上的 doFilter                    filterChain.doFilter(request.getRequest(),                            response.getResponse());                }            }         } // ...省略catch    }}

1. 获取wrapper, context
2. 加载servlet
3. 新建一个 filter 链表，servlet会放在 filter 链表最后，并且最后会调用servlet的service方法
4. 调用 filter 链表上的 doFilter

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5 总结

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转载请注明出处：http://blog.csdn.net/linxdcn/article/details/73800100