Tomcat中组件的生命周期管理公共接口Lifecycle

Tomcat的组件都会实现一个Lifecycle接口，以方便组件的生命周期的统一管理

interface Lifecycle

组件生命周期中主要的几个方法

增加监听器，事件委托机制
 public void addLifecycleListener(LifecycleListener listener);

public void removeLifecycleListener(LifecycleListener listener);
组件初始化
public void init() throws LifecycleException;

public void start() throws LifecycleException;
组件停止，当stop()方法执行完后会自动调用destroy()方法销毁组件
public void stop() throws LifecycleException;

public void destroy() throws LifecycleException;

 public LifecycleState getState();

事件有：

public static final String BEFORE_INIT_EVENT = "before_init";
public static final String AFTER_INIT_EVENT = "after_init";
public static final String START_EVENT = "start";
public static final String BEFORE_START_EVENT = "before_start";
public static final String AFTER_START_EVENT = "after_start";
public static final String STOP_EVENT = "stop";
public static final String BEFORE_STOP_EVENT = "before_stop";
public static final String AFTER_STOP_EVENT = "after_stop";
public static final String AFTER_DESTROY_EVENT = "after_destroy";
public static final String BEFORE_DESTROY_EVENT = "before_destroy";
public static final String PERIODIC_EVENT = "periodic";  //定期
public static final String CONFIGURE_START_EVENT = "configure_start";
public static final String CONFIGURE_STOP_EVENT = "configure_stop";

在tomcat启动过程中用到的几个组件，如StandardServer，StandardService，StandardEngine，StandardThreadExecutor，Connector等组件都间接实现了Lifecycle接口

如StandardServer

==>public final class StandardServer extends LifecycleMBeanBase implements Server

继承LifecycleMBeanBase

==>实现Server接口----不讨论

===>

public abstract class LifecycleMBeanBase extends LifecycleBase
implements JmxEnabled

===>public abstract class LifecycleBase implements Lifecycle

当调用StandardServer.init()方法时会调用Lifecycle.init()方法,

又因Lifecycle是接口，所以调用LifecycleBase这个接口的实现类LifecycleBase.init()

这个方法内部调用的LifecycleBase.initInternal()

在LifecycleBase中定义如下，就是一个抽象方法。需要继承这个类的所有组件实现这个方法。

protected abstract void initInternal() throws LifecycleException;

==》在LifecycleBase的子类中LifecycleMBeanBase中重写的这个initInternal（）

进行组件注册到MBeanServer组件管理服务器中，这里是所有组件进行初始化动作时的操作，最后还是要到StandardServer的initInternal()方法具体实现。

@Override
    protected void initInternal() throws LifecycleException {

        // If oname is not null then registration has already happened via
        // preRegister().
        if (oname == null) {
            mserver = Registry.getRegistry(null, null).getMBeanServer();

            oname = register(this, getObjectNameKeyProperties());
        }
    }

==》最后到StandardServer.initInternal()

---

上面的流程化简下：

StandardServer.init()

=>Lifecycle.init()

=>LifecycleBase.init()

=>LifecycleBase.initInternal()

=>LifecycleMBeanBase.initInternal()

=>StandardServer.initInternal()

StandardServer.init()最终调用的是StandardServer.initInternal()

同理，由上面的过程可以知道我们调用组件的start(),stop(),destroy()方法时最后调用的是组件的

startInternal()，stopInternal()，destroyInternal()方法。

也不清楚这是什么设计模式，当感觉这个组件生命周期管理方法值得学习