LifecycleMBeanBase
LifecycleMBeanBase
锦语冰 发表于1年前
LifecycleMBeanBase
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LifecycleMBeanBase被许多类继承,本文浅析之(由分析知——jmx是tomcat的基础)

LifecycleMBeanBase继承了LifecycleBase,实现了jmxEnabled,内部依赖org.apache.tomcat.util.modeler.Registry

分别用于生命周期的管理(start,init,stop,destroy),以及jmx——java拓展管理

1 生命周期

http://tomcat.apache.org/tomcat-9.0-doc/api/index.html

All Implemented Interfaces:

MBeanRegistrationJmxEnabledLifecycle

Direct Known Subclasses:

ConnectorContainerBaseFailedContextManagerBaseMapperListenerNamingResourcesImplRealmBaseSimpleTcpClusterStandardRoot,StandardServerStandardServiceStandardThreadExecutorValveBaseWebappLoader

Lifecycle:

主要实现start stop init destroy方法,并留有startInternal,stopInternal等方法给子类实现

/**
 * Common interface for component life cycle methods.  Catalina components
 * may implement this interface (as well as the appropriate interface(s) for
 * the functionality they support) in order to provide a consistent mechanism
 * to start and stop the component.
 * <br>
 * The valid state transitions for components that support {@link Lifecycle}
 * are:
 * <pre>
 *            start()
 *  -----------------------------
 *  |                           |
 *  | init()                    |
 * NEW -»-- INITIALIZING        |
 * | |           |              |     ------------------«-----------------------
 * | |           |auto          |     |                                        |
 * | |          \|/    start() \|/   \|/     auto          auto         stop() |
 * | |      INITIALIZED --»-- STARTING_PREP --»- STARTING --»- STARTED --»---  |
 * | |         |                                                            |  |
 * | |destroy()|                                                            |  |
 * | --»-----«--    ------------------------«--------------------------------  ^
 * |     |          |                                                          |
 * |     |         \|/          auto                 auto              start() |
 * |     |     STOPPING_PREP ----»---- STOPPING ------»----- STOPPED -----»-----
 * |    \|/                               ^                     |  ^
 * |     |               stop()           |                     |  |
 * |     |       --------------------------                     |  |
 * |     |       |                                              |  |
 * |     |       |    destroy()                       destroy() |  |
 * |     |    FAILED ----»------ DESTROYING ---«-----------------  |
 * |     |                        ^     |                          |
 * |     |     destroy()          |     |auto                      |
 * |     --------»-----------------    \|/                         |
 * |                                 DESTROYED                     |
 * |                                                               |
 * |                            stop()                             |
 * ----»-----------------------------»------------------------------
 *
 * Any state can transition to FAILED.
 *
 * Calling start() while a component is in states STARTING_PREP, STARTING or
 * STARTED has no effect.
 *
 * Calling start() while a component is in state NEW will cause init() to be
 * called immediately after the start() method is entered.
 *
 * Calling stop() while a component is in states STOPPING_PREP, STOPPING or
 * STOPPED has no effect.
 *
 * Calling stop() while a component is in state NEW transitions the component
 * to STOPPED. This is typically encountered when a component fails to start and
 * does not start all its sub-components. When the component is stopped, it will
 * try to stop all sub-components - even those it didn't start.
 *
 * Attempting any other transition will throw {@link LifecycleException}.
 *
 * </pre>
 * The {@link LifecycleEvent}s fired during state changes are defined in the
 * methods that trigger the changed. No {@link LifecycleEvent}s are fired if the
 * attempted transition is not valid.
 *
 * @author Craig R. McClanahan
 */
public interface Lifecycle {


    // ----------------------------------------------------- Manifest Constants


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


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


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


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


    /**
     * The LifecycleEvent type for the "component before stop" event.
     */
    public static final String BEFORE_STOP_EVENT = "before_stop";


    /**
     * The LifecycleEvent type for the "component after stop" event.
     */
    public static final String AFTER_STOP_EVENT = "after_stop";


    /**
     * The LifecycleEvent type for the "component after destroy" event.
     */
    public static final String AFTER_DESTROY_EVENT = "after_destroy";


    /**
     * The LifecycleEvent type for the "component before destroy" event.
     */
    public static final String BEFORE_DESTROY_EVENT = "before_destroy";


    /**
     * The LifecycleEvent type for the "periodic" event.
     */
    public static final String PERIODIC_EVENT = "periodic";


    /**
     * The LifecycleEvent type for the "configure_start" event. Used by those
     * components that use a separate component to perform configuration and
     * need to signal when configuration should be performed - usually after
     * {@link #BEFORE_START_EVENT} and before {@link #START_EVENT}.
     */
    public static final String CONFIGURE_START_EVENT = "configure_start";


    /**
     * The LifecycleEvent type for the "configure_stop" event. Used by those
     * components that use a separate component to perform configuration and
     * need to signal when de-configuration should be performed - usually after
     * {@link #STOP_EVENT} and before {@link #AFTER_STOP_EVENT}.
     */
    public static final String CONFIGURE_STOP_EVENT = "configure_stop";


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


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


    /**
     * Get the life cycle listeners associated with this life cycle.
     *
     * @return An array containing the life cycle listeners associated with this
     *         life cycle. If this component has no listeners registered, a
     *         zero-length array is returned.
     */
    public LifecycleListener[] findLifecycleListeners();


    /**
     * Remove a LifecycleEvent listener from this component.
     *
     * @param listener The listener to remove
     */
    public void removeLifecycleListener(LifecycleListener listener);


    /**
     * Prepare the component for starting. This method should perform any
     * initialization required post object creation. The following
     * {@link LifecycleEvent}s will be fired in the following order:
     * <ol>
     *   <li>INIT_EVENT: On the successful completion of component
     *                   initialization.</li>
     * </ol>
     *
     * @exception LifecycleException if this component detects a fatal error
     *  that prevents this component from being used
     */
    public void init() throws LifecycleException;

    /**
     * Prepare for the beginning of active use of the public methods other than
     * property getters/setters and life cycle methods of this component. This
     * method should be called before any of the public methods other than
     * property getters/setters and life cycle methods of this component are
     * utilized. The following {@link LifecycleEvent}s will be fired in the
     * following order:
     * <ol>
     *   <li>BEFORE_START_EVENT: At the beginning of the method. It is as this
     *                           point the state transitions to
     *                           {@link LifecycleState#STARTING_PREP}.</li>
     *   <li>START_EVENT: During the method once it is safe to call start() for
     *                    any child components. It is at this point that the
     *                    state transitions to {@link LifecycleState#STARTING}
     *                    and that the public methods other than property
     *                    getters/setters and life cycle methods may be
     *                    used.</li>
     *   <li>AFTER_START_EVENT: At the end of the method, immediately before it
     *                          returns. It is at this point that the state
     *                          transitions to {@link LifecycleState#STARTED}.
     *                          </li>
     * </ol>
     *
     * @exception LifecycleException if this component detects a fatal error
     *  that prevents this component from being used
     */
    public void start() throws LifecycleException;


    /**
     * Gracefully terminate the active use of the public methods other than
     * property getters/setters and life cycle methods of this component. Once
     * the STOP_EVENT is fired, the public methods other than property
     * getters/setters and life cycle methods should not be used. The following
     * {@link LifecycleEvent}s will be fired in the following order:
     * <ol>
     *   <li>BEFORE_STOP_EVENT: At the beginning of the method. It is at this
     *                          point that the state transitions to
     *                          {@link LifecycleState#STOPPING_PREP}.</li>
     *   <li>STOP_EVENT: During the method once it is safe to call stop() for
     *                   any child components. It is at this point that the
     *                   state transitions to {@link LifecycleState#STOPPING}
     *                   and that the public methods other than property
     *                   getters/setters and life cycle methods may no longer be
     *                   used.</li>
     *   <li>AFTER_STOP_EVENT: At the end of the method, immediately before it
     *                         returns. It is at this point that the state
     *                         transitions to {@link LifecycleState#STOPPED}.
     *                         </li>
     * </ol>
     *
     * Note that if transitioning from {@link LifecycleState#FAILED} then the
     * three events above will be fired but the component will transition
     * directly from {@link LifecycleState#FAILED} to
     * {@link LifecycleState#STOPPING}, bypassing
     * {@link LifecycleState#STOPPING_PREP}
     *
     * @exception LifecycleException if this component detects a fatal error
     *  that needs to be reported
     */
    public void stop() throws LifecycleException;

    /**
     * Prepare to discard the object. The following {@link LifecycleEvent}s will
     * be fired in the following order:
     * <ol>
     *   <li>DESTROY_EVENT: On the successful completion of component
     *                      destruction.</li>
     * </ol>
     *
     * @exception LifecycleException if this component detects a fatal error
     *  that prevents this component from being used
     */
    public void destroy() throws LifecycleException;


    /**
     * Obtain the current state of the source component.
     *
     * @return The current state of the source component.
     */
    public LifecycleState getState();


    /**
     * Obtain a textual representation of the current component state. Useful
     * for JMX. The format of this string may vary between point releases and
     * should not be relied upon to determine component state. To determine
     * component state, use {@link #getState()}.
     *
     * @return The name of the current component state.
     */
    public String getStateName();


    /**
     * Marker interface used to indicate that the instance should only be used
     * once. Calling {@link #stop()} on an instance that supports this interface
     * will automatically call {@link #destroy()} after {@link #stop()}
     * completes.
     */
    public interface SingleUse {
    }
}

主要定义事件的转态,事件的注册、注销等

lifeCycleBase

/**
 * 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 final Log log = LogFactory.getLog(LifecycleBase.class);

    private static final StringManager sm = StringManager.getManager(LifecycleBase.class);


    /**
     * The list of registered LifecycleListeners for event notifications.
     */
    private final List<LifecycleListener> lifecycleListeners = new CopyOnWriteArrayList<>();


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


    private boolean throwOnFailure = true;

    ......

}

其中用到了LifecycleListener和LlifeCycleState

/**
 * Interface defining a listener for significant events (including "component
 * start" and "component stop" generated by a component that implements the
 * Lifecycle interface. The listener will be fired after the associated state
 * change has taken place.
 *
 * @author Craig R. McClanahan
 */
public interface LifecycleListener {


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


}

/**
 * The list of valid states for components that implement {@link Lifecycle}.
 * See {@link Lifecycle} for the state transition diagram.
 */
public enum LifecycleState {
    NEW(false, null),
    INITIALIZING(false, Lifecycle.BEFORE_INIT_EVENT),
    INITIALIZED(false, Lifecycle.AFTER_INIT_EVENT),
    STARTING_PREP(false, Lifecycle.BEFORE_START_EVENT),
    STARTING(true, Lifecycle.START_EVENT),
    STARTED(true, Lifecycle.AFTER_START_EVENT),
    STOPPING_PREP(true, Lifecycle.BEFORE_STOP_EVENT),
    STOPPING(false, Lifecycle.STOP_EVENT),
    STOPPED(false, Lifecycle.AFTER_STOP_EVENT),
    DESTROYING(false, Lifecycle.BEFORE_DESTROY_EVENT),
    DESTROYED(false, Lifecycle.AFTER_DESTROY_EVENT),
    FAILED(false, null);

    private final boolean available;
    private final String lifecycleEvent;

    private LifecycleState(boolean available, String lifecycleEvent) {
        this.available = available;
        this.lifecycleEvent = lifecycleEvent;
    }

    /**
     * May the public methods other than property getters/setters and lifecycle
     * methods be called for a component in this state? It returns
     * <code>true</code> for any component in any of the following states:
     * <ul>
     * <li>{@link #STARTING}</li>
     * <li>{@link #STARTED}</li>
     * <li>{@link #STOPPING_PREP}</li>
     * </ul>
     *
     * @return <code>true</code> if the component is available for use,
     *         otherwise <code>false</code>
     */
    public boolean isAvailable() {
        return available;
    }

    public String getLifecycleEvent() {
        return lifecycleEvent;
    }
}

/**
 * General event for notifying listeners of significant changes on a component
 * that implements the Lifecycle interface.
 *
 * @author Craig R. McClanahan
 */
public final class LifecycleEvent extends EventObject {

    private static final long serialVersionUID = 1L;


    /**
     * Construct a new LifecycleEvent with the specified parameters.
     *
     * @param lifecycle Component on which this event occurred
     * @param type Event type (required)
     * @param data Event data (if any)
     */
    public LifecycleEvent(Lifecycle lifecycle, String type, Object data) {
        super(lifecycle);
        this.type = type;
        this.data = data;
    }


    /**
     * The event data associated with this event.
     */
    private final Object data;


    /**
     * The event type this instance represents.
     */
    private final String type;


    /**
     * @return the event data of this event.
     */
    public Object getData() {
        return data;
    }


    /**
     * @return the Lifecycle on which this event occurred.
     */
    public Lifecycle getLifecycle() {
        return (Lifecycle) getSource();
    }


    /**
     * @return the event type of this event.
     */
    public String getType() {
        return this.type;
    }
}

/**
 * <p>
 * The root class from which all event state objects shall be derived.
 * <p>
 * All Events are constructed with a reference to the object, the "source",
 * that is logically deemed to be the object upon which the Event in question
 * initially occurred upon.
 *
 * @since JDK1.1
 */

public class EventObject implements java.io.Serializable {

    private static final long serialVersionUID = 5516075349620653480L;

    /**
     * The object on which the Event initially occurred.
     */
    protected transient Object  source;

    /**
     * Constructs a prototypical Event.
     *
     * @param    source    The object on which the Event initially occurred.
     * @exception  IllegalArgumentException  if source is null.
     */
    public EventObject(Object source) {
        if (source == null)
            throw new IllegalArgumentException("null source");

        this.source = source;
    }

    /**
     * The object on which the Event initially occurred.
     *
     * @return   The object on which the Event initially occurred.
     */
    public Object getSource() {
        return source;
    }

    /**
     * Returns a String representation of this EventObject.
     *
     * @return  A a String representation of this EventObject.
     */
    public String toString() {
        return getClass().getName() + "[source=" + source + "]";
    }
}

注意LifecycleBase的lifecycleListeners是copyOnWriteList

@Override
public final synchronized void init() throws LifecycleException {
    if (!state.equals(LifecycleState.NEW)) {
        invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
    }

    try {
        setStateInternal(LifecycleState.INITIALIZING, null, false);
        initInternal();
        setStateInternal(LifecycleState.INITIALIZED, null, false);
    } catch (Throwable t) {
        handleSubClassException(t, "lifecycleBase.initFail", toString());
    }
}

init方法是个同步方法,如果state的状态不是new,会抛出LifecycleException异常

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

init方法调用initInternal(),是个抽象方法,留给子类实现

init方法两次调用setStateInternal方法,这也是同步方法,由于执行init的调用者已经获得当前对象的锁,所以会调用这个方法,而不阻塞(主要作用是触发监听其事件的监听器)

private synchronized void setStateInternal(LifecycleState state, Object data, boolean check)
        throws LifecycleException {

    if (log.isDebugEnabled()) {
        log.debug(sm.getString("lifecycleBase.setState", this, state));
    }

    if (check) {
        // Must have been triggered by one of the abstract methods (assume
        // code in this class is correct)
        // null is never a valid state
        if (state == null) {
            invalidTransition("null");
            // Unreachable code - here to stop eclipse complaining about
            // a possible NPE further down the method
            return;
        }

        // Any method can transition to failed
        // startInternal() permits STARTING_PREP to STARTING
        // stopInternal() permits STOPPING_PREP to STOPPING and FAILED to
        // STOPPING
        if (!(state == LifecycleState.FAILED ||
                (this.state == LifecycleState.STARTING_PREP &&
                        state == LifecycleState.STARTING) ||
                (this.state == LifecycleState.STOPPING_PREP &&
                        state == LifecycleState.STOPPING) ||
                (this.state == LifecycleState.FAILED &&
                        state == LifecycleState.STOPPING))) {
            // No other transition permitted
            invalidTransition(state.name());
        }
    }

    this.state = state;
    String lifecycleEvent = state.getLifecycleEvent();
    if (lifecycleEvent != null) {
        fireLifecycleEvent(lifecycleEvent, data);
    }
}

 

/**
 * 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) {
    LifecycleEvent event = new LifecycleEvent(this, type, data);
    for (LifecycleListener listener : lifecycleListeners) {
        listener.lifecycleEvent(event);
    }
}

这种处理异常的方式值得学习

private void handleSubClassException(Throwable t, String key, Object... args) throws LifecycleException {
    ExceptionUtils.handleThrowable(t);
    setStateInternal(LifecycleState.FAILED, null, false);
    String msg = sm.getString(key, args);
    if (getThrowOnFailure()) {
        if (!(t instanceof LifecycleException)) {
            t = new LifecycleException(msg, t);
        }
        throw (LifecycleException) t;
    } else {
        log.error(msg, t);
    }
}

这是start方法

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

    if (LifecycleState.STARTING_PREP.equals(state) || LifecycleState.STARTING.equals(state) ||
            LifecycleState.STARTED.equals(state)) {
        //如果正在启动中,则打印日志,return
        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();//如果状态是new,执行初始化
    } else if (state.equals(LifecycleState.FAILED)) {
        stop();//如果状态是failed,执行stop
    } else if (!state.equals(LifecycleState.INITIALIZED) &&
            !state.equals(LifecycleState.STOPPED)) {//如果已经初始化,或停止,抛异常
        invalidTransition(Lifecycle.BEFORE_START_EVENT);
    }

    try {
        setStateInternal(LifecycleState.STARTING_PREP, null, false);//设置全局state
        startInternal();
        if (state.equals(LifecycleState.FAILED)) {
            // This is a 'controlled' failure. The component put itself into the
            // FAILED state so call stop() to complete the clean-up.
            stop();
        } else if (!state.equals(LifecycleState.STARTING)) {
            // Shouldn't be necessary but acts as a check that sub-classes are
            // doing what they are supposed to.
            invalidTransition(Lifecycle.AFTER_START_EVENT);
        } else {
            setStateInternal(LifecycleState.STARTED, null, false);
        }
    } catch (Throwable t) {
        // This is an 'uncontrolled' failure so put the component into the
        // FAILED state and throw an exception.
        handleSubClassException(t, "lifecycleBase.startFail", toString());
    }
}

该方法会根据state值决定调用init,stop方法,以下是stop方法

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

    if (LifecycleState.STOPPING_PREP.equals(state) || LifecycleState.STOPPING.equals(state) ||
            LifecycleState.STOPPED.equals(state)) {//如果将、正在、已经stop

        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)) {
        invalidTransition(Lifecycle.BEFORE_STOP_EVENT);
    }

    try {
        if (state.equals(LifecycleState.FAILED)) {
            // Don't transition to STOPPING_PREP as that would briefly mark the
            // component as available but do ensure the BEFORE_STOP_EVENT is
            // fired
            fireLifecycleEvent(BEFORE_STOP_EVENT, null);
        } else {
            setStateInternal(LifecycleState.STOPPING_PREP, null, false);
        }

        stopInternal();

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

        setStateInternal(LifecycleState.STOPPED, null, false);
    } catch (Throwable t) {
        handleSubClassException(t, "lifecycleBase.stopFail", toString());
    } finally {
        if (this instanceof Lifecycle.SingleUse) {
            // Complete stop process first
            setStateInternal(LifecycleState.STOPPED, null, false);
            destroy();
        }
    }
}

如果其实现了Lifecycle.SingleUse接口,会调用destroy方法(有一点疑问,在destroy()方法里也会调用stop()方法,会有问题吗)

@Override
public final synchronized void destroy() throws LifecycleException {
    if (LifecycleState.FAILED.equals(state)) {
        try {
            // Triggers clean-up
            stop();
        } catch (LifecycleException e) {
            // Just log. Still want to destroy.
            log.warn(sm.getString(
                    "lifecycleBase.destroyStopFail", toString()), e);
        }
    }

    if (LifecycleState.DESTROYING.equals(state) || LifecycleState.DESTROYED.equals(state)) {
        if (log.isDebugEnabled()) {
            Exception e = new LifecycleException();
            log.debug(sm.getString("lifecycleBase.alreadyDestroyed", toString()), e);
        } else if (log.isInfoEnabled() && !(this instanceof Lifecycle.SingleUse)) {
            // Rather than have every component that might need to call
            // destroy() check for SingleUse, don't log an info message if
            // multiple calls are made to destroy()
            log.info(sm.getString("lifecycleBase.alreadyDestroyed", toString()));
        }

        return;
    }

    if (!state.equals(LifecycleState.STOPPED) && !state.equals(LifecycleState.FAILED) &&
            !state.equals(LifecycleState.NEW) && !state.equals(LifecycleState.INITIALIZED)) {
        invalidTransition(Lifecycle.BEFORE_DESTROY_EVENT);
    }//只有 停止ed,失败ed,初始化ed,new 可以destroy,pre ing不可以

    try {
        setStateInternal(LifecycleState.DESTROYING, null, false);
        destroyInternal();
        setStateInternal(LifecycleState.DESTROYED, null, false);
    } catch (Throwable t) {
        handleSubClassException(t, "lifecycleBase.destroyFail", toString());
    }
}

 

2 jmx

/**
 * This interface is implemented by components that will be registered with an
 * MBean server when they are created and unregistered when they are destroyed.
 * It is primarily intended to be implemented by components that implement
 * {@link Lifecycle} but is not exclusively for them.
 */
public interface JmxEnabled extends MBeanRegistration {

    /**
     * @return the domain under which this component will be / has been
     * registered.
     */
    String getDomain();


    /**
     * Specify the domain under which this component should be registered. Used
     * with components that cannot (easily) navigate the component hierarchy to
     * determine the correct domain to use.
     *
     * @param domain The name of the domain under which this component should be
     *               registered
     */
    void setDomain(String domain);


    /**
     * @return the name under which this component has been registered with JMX.
     */
    ObjectName getObjectName();
}

/**
 * <p>Can be implemented by an MBean in order to
 * carry out operations before and after being registered or unregistered from
 * the MBean Server.  An MBean can also implement this interface in order
 * to get a reference to the MBean Server and/or its name within that
 * MBean Server.</p>
 * 用于在mbean的注册前后、注销前后做相关操作
 * @since 1.5
 */
public interface MBeanRegistration   {


    /**
     * Allows the MBean to perform any operations it needs before
     * being registered in the MBean Server.  If the name of the MBean
     * is not specified, the MBean can provide a name for its
     * registration.  If any exception is raised, the MBean will not be
     * registered in the MBean Server.
     *
     * @param server The MBean Server in which the MBean will be registered.
     *
     * @param name The object name of the MBean.  This name is null if
     * the name parameter to one of the <code>createMBean</code> or
     * <code>registerMBean</code> methods in the {@link MBeanServer}
     * interface is null.  In that case, this method must return a
     * non-null ObjectName for the new MBean.
     *
     * @return The name under which the MBean is to be registered.
     * This value must not be null.  If the <code>name</code>
     * parameter is not null, it will usually but not necessarily be
     * the returned value.
     *
     * @exception java.lang.Exception This exception will be caught by
     * the MBean Server and re-thrown as an {@link
     * MBeanRegistrationException}.
     */
    public ObjectName preRegister(MBeanServer server,
                                  ObjectName name) throws java.lang.Exception;

    /**
     * Allows the MBean to perform any operations needed after having been
     * registered in the MBean server or after the registration has failed.
     * <p>If the implementation of this method throws a {@link RuntimeException}
     * or an {@link Error}, the MBean Server will rethrow those inside
     * a {@link RuntimeMBeanException} or {@link RuntimeErrorException},
     * respectively. However, throwing an exception in {@code postRegister}
     * will not change the state of the MBean:
     * if the MBean was already registered ({@code registrationDone} is
     * {@code true}), the MBean will remain registered. </p>
     * <p>This might be confusing for the code calling {@code createMBean()}
     * or {@code registerMBean()}, as such code might assume that MBean
     * registration has failed when such an exception is raised.
     * Therefore it is recommended that implementations of
     * {@code postRegister} do not throw Runtime Exceptions or Errors if it
     * can be avoided.</p>
     * @param registrationDone Indicates whether or not the MBean has
     * been successfully registered in the MBean server. The value
     * false means that the registration phase has failed.
     */
    public void postRegister(Boolean registrationDone);

    /**
     * Allows the MBean to perform any operations it needs before
     * being unregistered by the MBean server.
     *
     * @exception java.lang.Exception This exception will be caught by
     * the MBean server and re-thrown as an {@link
     * MBeanRegistrationException}.
     */
    public void preDeregister() throws java.lang.Exception ;

    /**
     * Allows the MBean to perform any operations needed after having been
     * unregistered in the MBean server.
     * <p>If the implementation of this method throws a {@link RuntimeException}
     * or an {@link Error}, the MBean Server will rethrow those inside
     * a {@link RuntimeMBeanException} or {@link RuntimeErrorException},
     * respectively. However, throwing an exception in {@code postDeregister}
     * will not change the state of the MBean:
     * the MBean was already successfully deregistered and will remain so. </p>
     * <p>This might be confusing for the code calling
     * {@code unregisterMBean()}, as it might assume that MBean deregistration
     * has failed. Therefore it is recommended that implementations of
     * {@code postDeregister} do not throw Runtime Exceptions or Errors if it
     * can be avoided.</p>
     */
    public void postDeregister();

 }

3 Registry

    注册表,用于创建、操作mbean,并简化其使用,其自身也是一个mbean。以下是其全局变量

/*
   Issues:
   - exceptions - too many "throws Exception"
   - double check the interfaces
   - start removing the use of the experimental methods in tomcat, then remove
     the methods ( before 1.1 final )
   - is the security enough to prevent Registry beeing used to avoid the permission
    checks in the mbean server ?
*/

/**
 * Registry for modeler MBeans.
 *
 * This is the main entry point into modeler. It provides methods to create
 * and manipulate model mbeans and simplify their use.
 *
 * This class is itself an mbean.
 *
 * IMPORTANT: public methods not marked with @since x.x are experimental or
 * internal. Should not be used.
 *
 * @author Craig R. McClanahan
 * @author Costin Manolache
 */
public class Registry implements RegistryMBean, MBeanRegistration  {
    /**
     * The Log instance to which we will write our log messages.
     */
    private static final Log log = LogFactory.getLog(Registry.class);

    // Support for the factory methods

    /** Will be used to isolate different apps and enhance security.
     *  隔离app并增强其安全性:key用来隔离,Registry.guard确保安全性
     */
    private static final HashMap<Object,Registry> perLoaderRegistries = null;

    /**
     * The registry instance created by our factory method the first time
     * it is called.所有注册表实例对应一个默认注册表
     */
    private static Registry registry = null;

    // Per registy fields

    /**
     * The <code>MBeanServer</code> instance that we will use to register
     * management beans. 所有注册表有自己的MBeanServer
     */
    private MBeanServer server = null;

    /**
     * The set of ManagedBean instances for the beans this registry
     * knows about, keyed by name.
     */
    private HashMap<String,ManagedBean> descriptors = new HashMap<>();

    /** List of managed beans, keyed by class name
     */
    private HashMap<String,ManagedBean> descriptorsByClass = new HashMap<>();

    // map to avoid duplicated searching or loading descriptors
    private HashMap<String,URL> searchedPaths = new HashMap<>();

    private Object guard;//守护者,用于阻止不信任的组件

    // Id - small ints to use array access. No reset on stop()
    // Used for notifications
    private final Hashtable<String,Hashtable<String,Integer>> idDomains =
        new Hashtable<>();
    private final Hashtable<String,int[]> ids = new Hashtable<>();

    getRegistry 获取注册表,静态同步方法,线程安全 

    /**
     * Factory method to create (if necessary) and return our
     * <code>Registry</code> instance.
     *
     * The current version uses a static - future versions could use
     * the thread class loader.
     *
     * @param key Support for application isolation. If null, the context class
     * loader will be used ( if setUseContextClassLoader is called ) or the
     * default registry is returned. key用于app隔离
     * @param guard Prevent access to the registry by untrusted components 用于阻止不信任的组件访问注册表
     * @return the registry
     * @since 1.1
     */
    public static synchronized Registry getRegistry(Object key, Object guard) {
        Registry localRegistry;
        if( perLoaderRegistries!=null ) {
            if( key==null )
                key=Thread.currentThread().getContextClassLoader();//获取当前线程的classLoader
            if( key != null ) {
                localRegistry = perLoaderRegistries.get(key);
                if( localRegistry == null ) {
                    localRegistry=new Registry();
//                    localRegistry.key=key;
                    localRegistry.guard=guard;
                    perLoaderRegistries.put( key, localRegistry );
                    return localRegistry;
                }
                if( localRegistry.guard != null &&
                        localRegistry.guard != guard ) {//验证守护者
                    return null; // XXX Should I throw a permission ex ?
                }
                return localRegistry;
            }
        }

        // static
        if (registry == null) {//registry是静态的(单例)
            registry = new Registry();
        }
        if( registry.guard != null &&
                registry.guard != guard ) {
            return null;
        }
        return (registry);
    }

    getMBeanServer 实例、同步方法  获取MBeanServer,可以看出,每个registry的MBeanServer是单例、延时加载的

    /**
     * Factory method to create (if necessary) and return our
     * <code>MBeanServer</code> instance.
     * @return the MBean server
     */
    public synchronized MBeanServer getMBeanServer() {
        if (server == null) {
            long t1 = System.currentTimeMillis();
            if (MBeanServerFactory.findMBeanServer(null).size() > 0) {
                server = MBeanServerFactory.findMBeanServer(null).get(0);
                if (log.isDebugEnabled()) {
                    log.debug("Using existing MBeanServer " + (System.currentTimeMillis() - t1));
                }
            } else {
                server = ManagementFactory.getPlatformMBeanServer();
                if (log.isDebugEnabled()) {
                    log.debug("Creating MBeanServer" + (System.currentTimeMillis() - t1));
                }
            }
        }
        return server;
    }

         下面方法根据给定的bean、objectName,动态生成DynamicMBean,并注册到MBeanServer

    /**
     * Register a component
     * 注册组件(jmx)
     * @param bean The bean
     * @param oname The object name
     * @param type The registry type
     * @throws Exception Error registering component
     */
    public void registerComponent(Object bean, ObjectName oname, String type)
           throws Exception
    {
        if( log.isDebugEnabled() ) {
            log.debug( "Managed= "+ oname);
        }

        if( bean ==null ) {
            log.error("Null component " + oname );
            return;
        }

        try {
            if( type==null ) {//当type传null时,type=bean的类名
                type=bean.getClass().getName();
            }

            ManagedBean managed = findManagedBean(null, bean.getClass(), type);

            // The real mbean is created and registered
            DynamicMBean mbean = managed.createMBean(bean);

            if(  getMBeanServer().isRegistered( oname )) {
                if( log.isDebugEnabled()) {
                    log.debug("Unregistering existing component " + oname );
                }
                getMBeanServer().unregisterMBean( oname );
            }

            getMBeanServer().registerMBean( mbean, oname);
        } catch( Exception ex) {
            log.error("Error registering " + oname, ex );
            throw ex;
        }
    }

4  LifecycleMBeanBase

    以下是全局变量,jmx部分可参考 https://my.oschina.net/u/1380557/blog/797972

    private static final Log log = LogFactory.getLog(LifecycleMBeanBase.class);//日志

    private static final StringManager sm =
        StringManager.getManager("org.apache.catalina.util");//日志信息


    /* Cache components of the MBean registration. */
    private String domain = null;//jmx domain
    private ObjectName oname = null;// jmx objectName
    protected MBeanServer mserver = null;//jmx MBeanServer

    这是initInternal方法,init方法/start方法会调用。作用是初始化MBeanServer,将当前对象转成MBean并注册到MBeanServer中。获取mserver的方法在上面,重点看register方法

    /**
     * Sub-classes wishing to perform additional initialization should override
     * this method, ensuring that super.initInternal() is the first call in the
     * overriding method.
     * 子类复写本方法时,需将super.initInternal()放第一行。与jmx的注册初始化相关
     */
    @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());
        }
    }

    /**
     * Utility method to enable sub-classes to easily register additional
     * components that don't implement {@link JmxEnabled} with an MBean server.
     * 方便子类注册组件到MBean server而不用实现JmxEabled
     * <br>
     * Note: This method should only be used once {@link #initInternal()} has
     * been called and before {@link #destroyInternal()} has been called.
     *
     * @param obj                       The object the register            要注册的对象
     * @param objectNameKeyProperties   The key properties component of the  objectName要用
     *                                  object name to use to register the
     *                                  object
     *
     * @return  The name used to register the object
     */
    protected final ObjectName register(Object obj,
            String objectNameKeyProperties) {

        // Construct an object name with the right domain
        StringBuilder name = new StringBuilder(getDomain());
        name.append(':');
        name.append(objectNameKeyProperties);

        ObjectName on = null;

        try {
            on = new ObjectName(name.toString());
            //根据给定的bean与ObjectName, 生成DynamicMBean, 并注册到MBeanServer
            Registry.getRegistry(null, null).registerComponent(obj, on, null);
        } catch (MalformedObjectNameException e) {
            log.warn(sm.getString("lifecycleMBeanBase.registerFail", obj, name),
                    e);
        } catch (Exception e) {
            log.warn(sm.getString("lifecycleMBeanBase.registerFail", obj, name),
                    e);
        }

        return on;
    }


    /**
     * Obtain the domain under which this component will be / has been
     * registered.
     */
    @Override
    public final String getDomain() {
        if (domain == null) {
            domain = getDomainInternal();
        }

        if (domain == null) {
            domain = Globals.DEFAULT_MBEAN_DOMAIN;
        }

        return domain;
    }

    /**
     * Method implemented by sub-classes to identify the domain in which MBeans
     * should be registered.
     *
     * @return  The name of the domain to use to register MBeans.
     */
    protected abstract String getDomainInternal();

这是destroyInternal方法

    /**
     * 子类复写此方法时,在方法的最后 super.destroyInternal()
     * Sub-classes wishing to perform additional clean-up should override this
     * method, ensuring that super.destroyInternal() is the last call in the
     * overriding method.
     */
    @Override
    protected void destroyInternal() throws LifecycleException {
        unregister(oname);
    }

    /**
     * Utility method to enable sub-classes to easily unregister additional
     * components that don't implement {@link JmxEnabled} with an MBean server.
     * <br>
     * Note: This method should only be used once {@link #initInternal()} has
     * been called and before {@link #destroyInternal()} has been called.
     *
     * @param on    The name of the component to unregister
     */
    protected final void unregister(ObjectName on) {

        // If null ObjectName, just return without complaint
        if (on == null) {
            return;
        }

        // If the MBeanServer is null, log a warning & return
        if (mserver == null) {
            log.warn(sm.getString("lifecycleMBeanBase.unregisterNoServer", on));
            return;
        }

        try {
            mserver.unregisterMBean(on);
        } catch (MBeanRegistrationException e) {
            log.warn(sm.getString("lifecycleMBeanBase.unregisterFail", on), e);
        } catch (InstanceNotFoundException e) {
            log.warn(sm.getString("lifecycleMBeanBase.unregisterFail", on), e);
        }

    }

        这是MBeanRegistration接口方法的实现,可以指定MBeanServer,  objectName, (因为在初始化时,都会先判空)

/**
 * Allows the object to be registered with an alternative
 * {@link MBeanServer} and/or {@link ObjectName}.
 */
@Override
public final ObjectName preRegister(MBeanServer server, ObjectName name)
        throws Exception {

    this.mserver = server;
    this.oname = name;
    this.domain = name.getDomain();

    return oname;
}

 

 

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