tomcat原理解析(二)：整体架构

一 整体结构

前面tomcat实现原理(一)里面描述了整个tomcat接受一个http请求的简单处理，这里面我们讲下整个tomcat的架构，以便对整体结构有宏观的了解。tomat里面由很多个容器结合在一起，主要有server,service,context,host,engine,wrapper,connector这7个容器来组装。当然了tomcat里面还有其它容器这里就不一一列举，因为我只看重点的。这7个容器存着父子关系，即可以通过当前容器找自己的父容器和自己的子容器。说到这我画了一个简单的结构图，让这种关系更加直观。如下：

根据图可以看出server是最外层的一个容器，它里面可以包含了Service容器，Service容器里面又包含了Connector和Engine，Engine容器里面又包含了Host，Host容器包含Context，Context容器包含Wrapper容器。就好比一个人有最外层的躯体，躯体里面有心脏，肺，胃，肾脏等等很多个个功能器件。

二 组件描述

       这里主要通过tomcat的源码来分析这7个容器是通过什么样的机制来组织在一起的，相互的包含的关系怎么处理。

 

      1.server组件

      server就像一个架子，很多其它子容器都装配在这个架子上。同时这个容器又暴露了一些入口对外提供服务。比如初始化服务，启动服务，停止服务等。源码中的server是一个接口，如下图:

查看Server接口类它还继承着Lifecycle接口，详情如下图：

Lifecycle接口控制着各个组件的生命周期，比如接口中的抽象方法init()初始化,start()启动,stop()停止,destory()销毁。 Server的标准实现类为StandardServer,细读StandardServer里面的接口addService,findServices的实现代码，可以看出这Service和 Server有着关联，Server可以有多个Service以数组的形式保存在其中。

 

public void addService(Service service) {

        service.setServer(this);

        synchronized (services) {
            Service results[] = new Service[services.length + 1];
            System.arraycopy(services, 0, results, 0, services.length);
            results[services.length] = service;
            services = results;

            if (getState().isAvailable()) {
                try {
                    service.start();
                } catch (LifecycleException e) {
                    // Ignore
                }
            }

            // Report this property change to interested listeners
            support.firePropertyChange("service", null, service);
        }

    }<span style="font-family:Microsoft YaHei;font-size:12px;">
</span>

 

1.将设置进来的Service 对象设置父组件为Server

2.重新构建了一个Service数组，然后将老的Service拷贝到新的数组中，同时追加新的Service组件

3.根据当前组件的生命状态，判断新加入的组件是否需要启动

    2.Service组件

        service接口它也继承Lifecycle接口。 前面说过了service组件的父组件是server组件，结构如下图：

它的标准实现是StandardService类，查看接口抽象方法addConnector的具体实现可以看出通过它可以给service容器添加connector容器，这里的connector就主要负责接收浏览器客户端发过来的http请求，仔细看里面的源码可以发现它接到请求时生成了一个socket对象，并将这个socket对象放入了一个线程中，同时线程会存入一个线程池来处理这次响应，并根据请求的详情信息来定位响应资源，响应的资源通过Engine容器给出。它就像浏览器和 Engine容器的桥梁，具体如何响应请求的会通过后面的章节来细说。先看是怎么将connector容器绑定到service中。 如下面代码：

public void addConnector(Connector connector) {
        synchronized (connectors) {
            connector.setService(this);
            Connector results[] = new Connector[connectors.length + 1];
            System.arraycopy(connectors, 0, results, 0, connectors.length);
            results[connectors.length] = connector;
            connectors = results;

            if (getState().isAvailable()) {
                try {
                    ((Lifecycle) connector).start();
                } catch (LifecycleException e) {
                    log.error("Connector.start", e);
                }
            }

            // Report this property change to interested listeners
            support.firePropertyChange("connector", null, connector);
        }

    }

1.给当前入去的Connector主键设置父容器service.
2.根据原有Connector集合的大小加上新加入的容器，从新构建了一个Connector数组。
3.将旧的数据拷贝到新的容器数组中，再添加新加的容器
4.然后根据当前容器的生命状态判断是否要启动新加入的容器
这里存放connector组件为什么用数组而不用List来存放不是太明白。感觉跟server管理service组件操作一样。看完所有的抽象接口是不是感觉有些奇怪，按照前面给的整体架构图怎么没看到给Service添加Engine组件的入口。查看Engine的标准实现类StandardEngine其实是实现了Container接口的，所以这里应该是通过setContainer接口设置进去的，其源码如下：

public void setContainer(Container container) {

        Container oldContainer = this.container;
        if ((oldContainer != null) && (oldContainer instanceof Engine))
            ((Engine) oldContainer).setService(null);
        this.container = container;
        if ((this.container != null) && (this.container instanceof Engine))
            ((Engine) this.container).setService(this);
        if (getState().isAvailable() && (this.container != null)) {
            try {
                this.container.start();
            } catch (LifecycleException e) {
                // Ignore
            }
        }
        if (getState().isAvailable() && (oldContainer != null)) {
            try {
                oldContainer.stop();
            } catch (LifecycleException e) {
                // Ignore
            }
        }

        // Report this property change to interested listeners
        support.firePropertyChange("container", oldContainer, this.container);

    }

 

1.将原有的Container（Engine）对象 的父对象置为空
2.同时将旧的Container对象覆盖掉，变成新注入的Container对象
3.同时根据当前组件的生命周期来判断是否将新注入的容器启动

3.Engine组件
Engine接口类为该组件的抽象接口，它继承Container接口跟前面描述的两个组件似乎有些不一样，查看源码后发现Container接口也继承了Lifecycle接口。Engine结构如下图：

它的标准实现是StandardEngine类，查setService接口的具体实现，service组件设置进Engine组件中，让两者之间关联。怎么没有看到添加子组件的入口呢？我们查看StandardEngine实现类中，它继承了ContainerBase类，而这个类实现了Container接口。在StandardEngine类中看到了addChild方法的实现 如下代码：

@Override
    public void addChild(Container child) {

        if (!(child instanceof Host))
            throw new IllegalArgumentException
                (sm.getString("standardEngine.notHost"));
        super.addChild(child);

    }<span style="font-family:Microsoft YaHei;font-size:12px;">
</span>

通过这个方法来为Engine添加子组件

1.判断当前传入的组件是否是Host类型的，否则抛异常

2.调用服务类中的addChild方法，同时将child变量传递到父类中处理，我们继续看父类ContainerBase中的代码。

public void addChild(Container child) {
        if (Globals.IS_SECURITY_ENABLED) {
            PrivilegedAction<Void> dp =
                new PrivilegedAddChild(child);
            AccessController.doPrivileged(dp);
        } else {
            addChildInternal(child);
        }
    }

    private void addChildInternal(Container child) {

        if( log.isDebugEnabled() )
            log.debug("Add child " + child + " " + this);
        synchronized(children) {
            if (children.get(child.getName()) != null)
                throw new IllegalArgumentException("addChild:  Child name '" +
                                                   child.getName() +
                                                   "' is not unique");
            child.setParent(this);  // May throw IAE
            children.put(child.getName(), child);

            // Start child
            if ((getState().isAvailable() ||
                    LifecycleState.STARTING_PREP.equals(getState())) &&
                    startChildren) {
                boolean success = false;
                try {
                    child.start();
                    success = true;
                } catch (LifecycleException e) {
                    log.error("ContainerBase.addChild: start: ", e);
                    throw new IllegalStateException
                        ("ContainerBase.addChild: start: " + e);
                } finally {
                    if (!success) {
                        children.remove(child.getName());
                    }
                }
            }

            fireContainerEvent(ADD_CHILD_EVENT, child);
        }

    }

最终它调用了addChildInternal方法来处理。

child.setParent(this);
children.put(child.getName(), child);
1.这里传入host子组件的同时，给host子组件设置了父组件
2.将子组件保存在children变量中，这里的children其实就是个HashMap对象。
看到这里也就明白了，所有继承ContainerBase类的组件在添加子组件都是依赖父类中的MAP对象来保存的.

4.Host组件
Host类为该组件的接口定义，也继承了Container类，它的标准实现是StandardHost类，继承ContainerBase类。host结构如下图所示：

因为该标准实现类StandardHost也继承了ContainerBase类，所以该组件的子组件添加也依赖父类中的Map来保存，跟Engine组件管理子组件是一样的。每一个HOST相当于一个主机，并负责展开和运行多个部署进去的war包。每个主机下面有多个部署的应用，一个应用就对应着一个Context。通过context将多个应用分隔开。所以host的子组件就是context，在通过ContainerBase类的addChild方法来添加context子容器的同时也给它设置了父容器host对象。

5.Context容器

context接口继承了Container，StandardContext类为是Context的标准实现，它也继承了ContainerBase类，所以给改容器注入子容器也是通过containerBase类中的addaddChild来处理的。Context容器代表着一个servlet容器，它为servlet运行提供环境。context管理着里面servlet实例，servlet实例在context中以Wrapper形式存在。那么一个http请求是怎么找到对应的servlet实例的呢？后面章节再来详细描述

 

6.Wrapper容器

Wrapper接口类也继承Container类，它的标准实现类是StandardWrapper，也继承了ContainerBase类。因为Wrapper容器是最底层的容器了，所以它不存在子容器。Wrapper 代表一个Servlet，它负责管理一个 Servlet，包括的 Servlet的装载、初始化、执行以及资源回收。

 

 

三 组件相关类结构

     上面小节描述将各个容器编织到一起，阅读相关容器的代码结构可以整理出如下类的继承关系。从类的关系图可以看出所有的容器都实现了Lifecycle接口，该接口定义了控制着tomcat的初始化，启动，停止，销毁等抽象操作。具体的实现都留给了子类实现。

 

      

 

 

仔细查看上面的结构图，可以发现LifecycleBase比较陌生，在前面章节没怎么提到过。LifecycleBase类实现了Lifecycle接口，它实现了Lifecycle接口中的init()start()stop()destroy()。我们看看LifecycleBase中的类是怎么实现的，源码如下：

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.catalina.util;

import org.apache.catalina.Lifecycle;
import org.apache.catalina.LifecycleException;
import org.apache.catalina.LifecycleListener;
import org.apache.catalina.LifecycleState;
import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
import org.apache.tomcat.util.res.StringManager;


/**
 * Base implementation of the {@link Lifecycle} interface that implements the
 * state transition rules for {@link Lifecycle#start()} and
 * {@link Lifecycle#stop()}
 */
public abstract class LifecycleBase implements Lifecycle {

    private static Log log = LogFactory.getLog(LifecycleBase.class);

    private static StringManager sm =
        StringManager.getManager("org.apache.catalina.util");


    /**
     * Used to handle firing lifecycle events.
     * TODO: Consider merging LifecycleSupport into this class.
     */
    private LifecycleSupport lifecycle = new LifecycleSupport(this);


    /**
     * The current state of the source component.
     */
    private volatile LifecycleState state = LifecycleState.NEW;


    /**
     * {@inheritDoc}
     */
    @Override
    public void addLifecycleListener(LifecycleListener listener) {
        lifecycle.addLifecycleListener(listener);
    }


    /**
     * {@inheritDoc}
     */
    @Override
    public LifecycleListener[] findLifecycleListeners() {
        return lifecycle.findLifecycleListeners();
    }


    /**
     * {@inheritDoc}
     */
    @Override
    public void removeLifecycleListener(LifecycleListener listener) {
        lifecycle.removeLifecycleListener(listener);
    }


    /**
     * Allow sub classes to fire {@link Lifecycle} events.
     *
     * @param type  Event type
     * @param data  Data associated with event.
     */
    protected void fireLifecycleEvent(String type, Object data) {
        lifecycle.fireLifecycleEvent(type, data);
    }


    public synchronized final void init() throws LifecycleException {
        if (!state.equals(LifecycleState.NEW)) {
            invalidTransition(Lifecycle.INIT_EVENT);
        }
       //1.实现初始化的方法，最终是调用了当前类的initInternal方法,发现
initInternal抽象的


        initInternal();

        setState(LifecycleState.INITIALIZED);
    }


    protected abstract void initInternal() throws LifecycleException;

    /**
     * {@inheritDoc}
     */
    @Override
    public synchronized final void start() throws LifecycleException {

        if (LifecycleState.STARTING_PREP.equals(state) ||
                LifecycleState.STARTING.equals(state) ||
                LifecycleState.STARTED.equals(state)) {

            if (log.isDebugEnabled()) {
                Exception e = new LifecycleException();
                log.debug(sm.getString("lifecycleBase.alreadyStarted",
                        toString()), e);
            } else if (log.isInfoEnabled()) {
                log.info(sm.getString("lifecycleBase.alreadyStarted",
                        toString()));
            }

            return;
        }

        if (state.equals(LifecycleState.NEW)) {
            init();
        } else if (!state.equals(LifecycleState.INITIALIZED) &&
                !state.equals(LifecycleState.STOPPED)) {
            invalidTransition(Lifecycle.BEFORE_START_EVENT);
        }

        setState(LifecycleState.STARTING_PREP);

        try {
 //2.实现初始化的方法，最终是调用了当前类的startInternal方法,发现startInternal抽象的

            startInternal();
        } catch (LifecycleException e) {
            setState(LifecycleState.FAILED);
            throw e;
        }

        if (state.equals(LifecycleState.FAILED) ||
                state.equals(LifecycleState.MUST_STOP)) {
            stop();
        } else {
            // Shouldn't be necessary but acts as a check that sub-classes are
            // doing what they are supposed to.
            if (!state.equals(LifecycleState.STARTING)) {
                invalidTransition(Lifecycle.AFTER_START_EVENT);
            }

            setState(LifecycleState.STARTED);
        }
    }


    /**
     * Sub-classes must ensure that:
     * <ul>
     * <li>the {@link Lifecycle#START_EVENT} is fired during the execution of
     *     this method</li>
     * <li>the state is changed to {@link LifecycleState#STARTING} when the
     *     {@link Lifecycle#START_EVENT} is fired
     * </ul>
     *
     * If a component fails to start it may either throw a
     * {@link LifecycleException} which will cause it's parent to fail to start
     * or it can place itself in the error state in which case {@link #stop()}
     * will be called on the failed component but the parent component will
     * continue to start normally.
     *
     * @throws LifecycleException
     */
    protected abstract void startInternal() throws LifecycleException;


    /**
     * {@inheritDoc}
     */
    @Override
    public synchronized final void stop() throws LifecycleException {

        if (LifecycleState.STOPPING_PREP.equals(state) ||
                LifecycleState.STOPPING.equals(state) ||
                LifecycleState.STOPPED.equals(state)) {

            if (log.isDebugEnabled()) {
                Exception e = new LifecycleException();
                log.debug(sm.getString("lifecycleBase.alreadyStopped",
                        toString()), e);
            } else if (log.isInfoEnabled()) {
                log.info(sm.getString("lifecycleBase.alreadyStopped",
                        toString()));
            }

            return;
        }

        if (state.equals(LifecycleState.NEW)) {
            state = LifecycleState.STOPPED;
            return;
        }

        if (!state.equals(LifecycleState.STARTED) &&
                !state.equals(LifecycleState.FAILED) &&
                !state.equals(LifecycleState.MUST_STOP)) {
            invalidTransition(Lifecycle.BEFORE_STOP_EVENT);
        }

        setState(LifecycleState.STOPPING_PREP);
 //3.实现初始化的方法，最终是调用了当前类的stopInternal方法,发现stopInternal抽象的

        stopInternal();

        if (state.equals(LifecycleState.MUST_DESTROY)) {
            // Complete stop process first
            setState(LifecycleState.STOPPED);

            destroy();
        } else {
            // Shouldn't be necessary but acts as a check that sub-classes are doing
            // what they are supposed to.
            if (!state.equals(LifecycleState.STOPPING)) {
                invalidTransition(Lifecycle.AFTER_STOP_EVENT);
            }

            setState(LifecycleState.STOPPED);
        }
    }


    /**
     * Sub-classes must ensure that:
     * <ul>
     * <li>the {@link Lifecycle#STOP_EVENT} is fired during the execution of
     *     this method</li>
     * <li>the state is changed to {@link LifecycleState#STOPPING} when the
     *     {@link Lifecycle#STOP_EVENT} is fired
     * </ul>
     *
     * @throws LifecycleException
     */
    protected abstract void stopInternal() throws LifecycleException;


    public synchronized final void destroy() throws LifecycleException {
        if (LifecycleState.DESTROYED.equals(state)) {

            if (log.isDebugEnabled()) {
                Exception e = new LifecycleException();
                log.debug(sm.getString("lifecycleBase.alreadyDestroyed",
                        toString()), e);
            } else if (log.isInfoEnabled()) {
                log.info(sm.getString("lifecycleBase.alreadyDestroyed",
                        toString()));
            }

            return;
        }

        if (!state.equals(LifecycleState.STOPPED) &&
                !state.equals(LifecycleState.FAILED) &&
                !state.equals(LifecycleState.NEW)) {
            invalidTransition(Lifecycle.DESTROY_EVENT);
        }
 //4.实现初始化的方法，最终是调用了当前类的destroyInternal方法,发现destroyInternal抽象的

        destroyInternal();

        setState(LifecycleState.DESTROYED);
    }


    protected abstract void destroyInternal() throws LifecycleException;

    /**
     * {@inheritDoc}
     */
    public LifecycleState getState() {
        return state;
    }


    /**
     * Provides a mechanism for sub-classes to update the component state.
     * Calling this method will automatically fire any associated
     * {@link Lifecycle} event.
     *
     * @param state The new state for this component
     */
    protected synchronized void setState(LifecycleState state) {
        setState(state, null);
    }


    /**
     * Provides a mechanism for sub-classes to update the component state.
     * Calling this method will automatically fire any associated
     * {@link Lifecycle} event.
     *
     * @param state The new state for this component
     * @param data  The data to pass to the associated {@link Lifecycle} event
     */
    protected synchronized void setState(LifecycleState state, Object data) {

        if (log.isDebugEnabled()) {
            log.debug(sm.getString("lifecycleBase.setState", this, state));
        }
        this.state = state;
        String lifecycleEvent = state.getLifecycleEvent();
        if (lifecycleEvent != null) {
            fireLifecycleEvent(lifecycleEvent, data);
        }
    }


    private void invalidTransition(String type) throws LifecycleException {
        String msg = sm.getString("lifecycleBase.invalidTransition", type,
                toString(), state);
        throw new LifecycleException(msg);
    }
}

阅读以上LifecycleBase类中的源码，在第1,2,3,4处分别实现了init(),start(),stop(),destroy()等方法。分析其方法体中内容，实现代码最终还是调用了当前类中的initInternal(),startInternal(),stopInternal(),destroyInternal()等方法，而且这些方法还是抽象的。也就是说在执行这些方法时，最终是执行子类的具体实现。这貌似就是设计模式中的抽象模版方法模式哦！

 

四 总结

 

      阅读到这，大家应该对tomcat的整体架构和各个容器如何交织在一起有了一定的了解。并在第三节我粗略的分析了下容器的初始化，启动，停止，销毁等生命周期的控制，从结构上看使用了抽象模版方法模式，所以掌握23种设计模式还是非常有用的在阅读源码或自己做设计方面 。了解了这些您是否会再思考，这些容器是什么时候或什么事件来触发装配在一起操作的哇！。下一个章节就来说说容器的初始化吧，它会给出前面的答案！