tomcat 7 源码分析-8 生命周期lifecycle和监听listener

tomcat 7 源码分析-8 生命周期lifecycle和监听listener

 

每个应用都有生命周期lifecycle，可能包括init,start,stop,destroy等更多。针对生命周期的变化，如何做变化作出反 应，tomcat在设计的时候，把时间监听listener结合起来，所以listener取的名字是lifecyclelistener，对 lifecycle进行监听。

总的最底层的来自两个interface的设计Lifecycle和LifecycleListener。

lifecycle这个接口定义了除本身生命周期的函数，另外还定义了整个生命周期阶段的事件类型(这个肯定是为 lifecyclelistener准备的)，同时还对LifecycleListener有增加，删除，通知等的函数。 LifecycleListener这个接口定义了对事件Event的反应。简单看下Lifecycle和LifecycleListener的代码片 段。

public
 
interface
 Lifecycle {

    /**
     * The LifecycleEvent type for the "component init" event.
     */
    public
 
static
 
final
 String INIT_EVENT = 
"init"
;


    /**
     * The LifecycleEvent type for the "component start" event.
     */
    public
 
static
 
final
 String START_EVENT = 
"start"
;


    /**
     * The LifecycleEvent type for the "component before start" event.
     */
    public
 
static
 
final
 String BEFORE_START_EVENT = 
"before_start"
;

    [..........]

    // --------------------------------------------------------- Public Methods


    /**
     * Add a LifecycleEvent listener to this component.
     *
     * @param listener The listener to add
     */
    public
 
void
 addLifecycleListener(LifecycleListener listener);


    /**
     * Get the lifecycle listeners associated with this lifecycle. If this
     * Lifecycle has no listeners registered, a zero-length array is returned.
     */
    public
 LifecycleListener[] findLifecycleListeners();

    [.............]

    public
 
void
 init() 
throws
 LifecycleException;

    public
 
void
 start() 
throws
 LifecycleException;

    public
 
void
 stop() 
throws
 LifecycleException;

    public
 
void
 destroy() 
throws
 LifecycleException;

    public
 LifecycleState getState();
}

public interface Lifecycle {

    /**
     * The LifecycleEvent type for the "component init" event.
     */
    public static final String INIT_EVENT = "init";


    /**
     * The LifecycleEvent type for the "component start" event.
     */
    public static final String START_EVENT = "start";


    /**
     * The LifecycleEvent type for the "component before start" event.
     */
    public static final String BEFORE_START_EVENT = "before_start";

    [..........]
    
    // --------------------------------------------------------- Public Methods


    /**
     * Add a LifecycleEvent listener to this component.
     *
     * @param listener The listener to add
     */
    public void addLifecycleListener(LifecycleListener listener);


    /**
     * Get the lifecycle listeners associated with this lifecycle. If this 
     * Lifecycle has no listeners registered, a zero-length array is returned.
     */
    public LifecycleListener[] findLifecycleListeners();

    [.............]

    public void init() throws LifecycleException;

    public void start() throws LifecycleException;

    public void stop() throws LifecycleException;

    public void destroy() throws LifecycleException;

    public LifecycleState getState();
}

 

public
 
interface
 LifecycleListener {


    /**
     * Acknowledge the occurrence of the specified event.
     *
     * @param event LifecycleEvent that has occurred
     */
    public
 
void
 lifecycleEvent(LifecycleEvent event);


}

public interface LifecycleListener {


    /**
     * Acknowledge the occurrence of the specified event.
     *
     * @param event LifecycleEvent that has occurred
     */
    public void lifecycleEvent(LifecycleEvent event);


}

 后续的问题是，谁来维护LifecycleListener？谁维护LifecycleListener，必然要提供真正意思上对操作(增，删， 查和通知)函数。Tomcat将这些交给了LifecycleSupport。同时LifecycleSupport还提供对lifecycle传来的 bype，data封装成

LifecycleEvent类，给LifecycleListener用。

public
 
final
 
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;
        }

    }


}

public final 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;
        }

    }


}

tomcat的应用都继承之Lifecycle，包括server，service，Connector，GlobalNamingResources等，而针对这些又实现不同的LifecycleListener。