Tomcat由多个组件组成，那么Tomcat是怎么对他们的生命周期进行管理的么，这里将从Tomcat源码去分析其生命周期的实现；

Bootstrape类为Tomcat的入口，所有的组件够通过实现Lifecycle接口来管理生命周期，Tomcat启动的时候只需调用Server容器的start()，然后父容器依序启动他所包含的子容器，关闭也是如此。

     通过阅读源码可知一个Server里包含一个或多个Service，一个Service里包含一个Container，一个或多个Connector、Container又包含了Engine、Host、Context、Wrapper四个容器；

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Tomcat的组件启动顺序为： 

StandardServer.start()——》StandardServer.startInternal() ——》StandardService().start()——StandardService.startInternal() ——>》StandardEngine().start() ——》StandardEngine.startInternal()—》StandardEngine中启动其他组件，组件关闭也是如此；

现在我们通过Demo简单模拟Tomcat的启动

                                                                        模拟Demo UML类图

                                                                    模拟Demo时序图

主要代码段如下：

Catalina类：

package co.solinx.Pattern.Observer;/** * Created by LX on 2014/11/26. */public class Catalina {    public static void main(String[] args) {        //Tomcat为多个组件组成的server为最外围最大的一个        StandardServer server = new StandardServer();
        //为server添加监听器        server.addLifecycleListener(new ContextConfig());        //添加一个service        StandardService service = new StandardService();        server.AddService(service);
       //为service添加监听器        service.addLifecycleListener(new ContextConfig());        //添加一个engine        StandardEngine standardEngine = new StandardEngine();
        //为engine添加监听器        standardEngine.addLifecycleListener(new EngineConfig());        StandardHost standardHost = new StandardHost("localhost");//        StandardHost testHost = new StandardHost("test");//        standardHost.addLifecycleListener(new EngineConfig());        standardEngine.addChild("localhost", standardHost);//        standardEngine.addChild("test", testHost);        //往service添加engine容器        service.setContainer(standardEngine);        try {            server.start();        } catch (LifecycleException e) {            e.printStackTrace();        }    }}

StandardServer类

package co.solinx.Pattern.Observer;/** * Created by LX on 2014/11/26. */public class StandardServer extends LifecycleBase implements Context {    Service services[] = new Service[0];    @Override    protected void startInternal() throws LifecycleException {        for (int i = 0; i < services.length; i++) {            services[i].start();        }        System.out.println("StandardServer start");    }    public void AddService(Service service) {        Service result[] = new Service[services.length + 1];        System.arraycopy(services, 0, result, 0, services.length);        result[services.length] = service;        services = result;    }    }

StandardService类：

package co.solinx.Pattern.Observer;/** * Created by LX on 2014/11/26. */public class StandardService extends LifecycleBase implements Service, Context {    protected ContainerBase container = null;    @Override    protected void startInternal() throws LifecycleException {        container.start();        System.out.println("StandardService start");    }    public void setContainer(ContainerBase container) {        this.container = container;    }}

StandardEngine类：

package co.solinx.Pattern.Observer;/** * Created by LX on 2014/11/26. */public class StandardEngine extends ContainerBase {    @Override    protected void startInternal() throws LifecycleException {        super.startInternal();        System.out.println("StandardEngine start");    }    protected void addChild(String key, Container container) {        super.addChild(key, container);    }}

LifecycleSupport类：

package co.solinx.Pattern.Observer;/** * Created by LX on 2014/11/26. * 代理了具体监听者 */public class LifecycleSupport {    public LifecycleSupport(Lifecycle lifecycle) {        super();        this.lifecycle = lifecycle;    }    private Lifecycle lifecycle = null;    private LifecycleListener listeners[] = new LifecycleListener[0];    private final Object listenersLock = new Object(); // Lock object for changes to listeners    public void addLifecycleListener(LifecycleListener listener) {        synchronized (listenersLock) {            LifecycleListener results[] =                    new LifecycleListener[listeners.length + 1];            for (int i = 0; i < listeners.length; i++)                results[i] = listeners[i];            results[listeners.length] = listener;            listeners = results;        }    }    public LifecycleListener[] findLifecycleListeners() {        return listeners;    }    public void fireLifecycleEvent(String type, Object data) {        LifecycleEvent event = new LifecycleEvent(lifecycle, type, data);        LifecycleListener interested[] = listeners;        for (int i = 0; i < interested.length; i++)            interested[i].lifecycleEvent(event);    }    public void removeLifecycleListener(LifecycleListener listener) {        synchronized (listenersLock) {            int n = -1;            for (int i = 0; i < listeners.length; i++) {                if (listeners[i] == listener) {                    n = i;                    break;                }            }            if (n < 0)                return;            LifecycleListener results[] =                    new LifecycleListener[listeners.length - 1];            int j = 0;            for (int i = 0; i < listeners.length; i++) {                if (i != n)                    results[j++] = listeners[i];            }            listeners = results;        }    }}

模拟程序运行结果：

文章首发地址：Solinx 

http://www.solinx.co/archives/86

Tomcat源码分析之—组件启动实现分析