spring源码分析之spring jmx

<beans>

    <bean id="mbeanServer" class="org.springframework.jmx.support.MBeanServerFactoryBean"/>

    <!--
    this bean needs to be eagerly pre-instantiated in order for the exporting to occur;
    this means that it must not be marked as lazily initialized
    -->
    <bean id="exporter" class="org.springframework.jmx.export.MBeanExporter">
        <property name="beans">
            <map>
                <entry key="bean:name=testBean1" value-ref="testBean"/>
            </map>
        </property>
        <property name="server" ref="mbeanServer"/>
    </bean>

    <bean id="testBean" class="org.springframework.jmx.JmxTestBean">
        <property name="name" value="TEST"/>
        <property name="age" value="100"/>
    </bean>

</beans>

/**
     * Creates the {@code MBeanServer} instance.
     */
    @Override
    public void afterPropertiesSet() throws MBeanServerNotFoundException {
        // Try to locate existing MBeanServer, if desired.
        if (this.locateExistingServerIfPossible || this.agentId != null) {
            try {
                this.server = locateMBeanServer(this.agentId);
            }
            catch (MBeanServerNotFoundException ex) {
                // If agentId was specified, we were only supposed to locate that
                // specific MBeanServer; so let‘s bail if we can‘t find it.
                if (this.agentId != null) {
                    throw ex;
                }
                logger.info("No existing MBeanServer found - creating new one");
            }
        }

        // Create a new MBeanServer and register it, if desired.
        if (this.server == null) {
            this.server = createMBeanServer(this.defaultDomain, this.registerWithFactory);
            this.newlyRegistered = this.registerWithFactory;
        }
    }

    /**
     * Create a new {@code MBeanServer} instance and register it with the
     * {@code MBeanServerFactory}, if desired.
     * @param defaultDomain the default domain, or {@code null} if none
     * @param registerWithFactory whether to register the {@code MBeanServer}
     * with the {@code MBeanServerFactory}
     * @see javax.management.MBeanServerFactory#createMBeanServer
     * @see javax.management.MBeanServerFactory#newMBeanServer
     */
    protected MBeanServer createMBeanServer(String defaultDomain, boolean registerWithFactory) {
        if (registerWithFactory) {
            return MBeanServerFactory.createMBeanServer(defaultDomain);
        }
        else {
            return MBeanServerFactory.newMBeanServer(defaultDomain);
        }
    }

/**
     * Kick off bean registration automatically when deployed in an {@code ApplicationContext}.
     * @see #registerBeans()
     */
    @Override
    public void afterPropertiesSet() {
        // If no server was provided then try to find one. This is useful in an environment
        // where there is already an MBeanServer loaded.
        if (this.server == null) {
            this.server = JmxUtils.locateMBeanServer();
        }

        try {
            logger.info("Registering beans for JMX exposure on startup");
            registerBeans();
            registerNotificationListeners();
        }
        catch (RuntimeException ex) {
            // Unregister beans already registered by this exporter.
            unregisterNotificationListeners();
            unregisterBeans();
            throw ex;
        }
    }

//---------------------------------------------------------------------
    // Exporter implementation
    //---------------------------------------------------------------------

    /**
     * Registers the defined beans with the {@link MBeanServer}.
     * <p>Each bean is exposed to the {@code MBeanServer} via a
     * {@code ModelMBean}. The actual implemetation of the
     * {@code ModelMBean} interface used depends on the implementation of
     * the {@code ModelMBeanProvider} interface that is configured. By
     * default the {@code RequiredModelMBean} class that is supplied with
     * all JMX implementations is used.
     * <p>The management interface produced for each bean is dependent on the
     * {@code MBeanInfoAssembler} implementation being used. The
     * {@code ObjectName} given to each bean is dependent on the
     * implementation of the {@code ObjectNamingStrategy} interface being used.
     */
    protected void registerBeans() {
        // The beans property may be null, for example if we are relying solely on autodetection.
        if (this.beans == null) {
            this.beans = new HashMap<String, Object>();
            // Use AUTODETECT_ALL as default in no beans specified explicitly.
            if (this.autodetectMode == null) {
                this.autodetectMode = AUTODETECT_ALL;
            }
        }

        // Perform autodetection, if desired.
        int mode = (this.autodetectMode != null ? this.autodetectMode : AUTODETECT_NONE);
        if (mode != AUTODETECT_NONE) {
            if (this.beanFactory == null) {
                throw new MBeanExportException("Cannot autodetect MBeans if not running in a BeanFactory");
            }
            if (mode == AUTODETECT_MBEAN || mode == AUTODETECT_ALL) {
                // Autodetect any beans that are already MBeans.
                logger.debug("Autodetecting user-defined JMX MBeans");
                autodetectMBeans();
            }
            // Allow the assembler a chance to vote for bean inclusion.
            if ((mode == AUTODETECT_ASSEMBLER || mode == AUTODETECT_ALL) &&
                    this.assembler instanceof AutodetectCapableMBeanInfoAssembler) {
                autodetectBeans((AutodetectCapableMBeanInfoAssembler) this.assembler);
            }
        }

        if (!this.beans.isEmpty()) {
            for (Map.Entry<String, Object> entry : this.beans.entrySet()) {
                registerBeanNameOrInstance(entry.getValue(), entry.getKey());
            }
        }
    }

/**
     * Registers an individual bean with the {@link #setServer MBeanServer}.
     * <p>This method is responsible for deciding <strong>how</strong> a bean
     * should be exposed to the {@code MBeanServer}. Specifically, if the
     * supplied {@code mapValue} is the name of a bean that is configured
     * for lazy initialization, then a proxy to the resource is registered with
     * the {@code MBeanServer} so that the the lazy load behavior is
     * honored. If the bean is already an MBean then it will be registered
     * directly with the {@code MBeanServer} without any intervention. For
     * all other beans or bean names, the resource itself is registered with
     * the {@code MBeanServer} directly.
     * @param mapValue the value configured for this bean in the beans map;
     * may be either the {@code String} name of a bean, or the bean itself
     * @param beanKey the key associated with this bean in the beans map
     * @return the {@code ObjectName} under which the resource was registered
     * @throws MBeanExportException if the export failed
     * @see #setBeans
     * @see #registerBeanInstance
     * @see #registerLazyInit
     */
    protected ObjectName registerBeanNameOrInstance(Object mapValue, String beanKey) throws MBeanExportException {
        try {
            if (mapValue instanceof String) {
                // Bean name pointing to a potentially lazy-init bean in the factory.
                if (this.beanFactory == null) {
                    throw new MBeanExportException("Cannot resolve bean names if not running in a BeanFactory");
                }
                String beanName = (String) mapValue;
                if (isBeanDefinitionLazyInit(this.beanFactory, beanName)) {
                    ObjectName objectName = registerLazyInit(beanName, beanKey);
                    replaceNotificationListenerBeanNameKeysIfNecessary(beanName, objectName);
                    return objectName;
                }
                else {
                    Object bean = this.beanFactory.getBean(beanName);
                    ObjectName objectName = registerBeanInstance(bean, beanKey);
                    replaceNotificationListenerBeanNameKeysIfNecessary(beanName, objectName);
                    return objectName;
                }
            }
            else {
                // Plain bean instance -> register it directly.
                if (this.beanFactory != null) {
                    Map<String, ?> beansOfSameType =
                            this.beanFactory.getBeansOfType(mapValue.getClass(), false, this.allowEagerInit);
                    for (Map.Entry<String, ?> entry : beansOfSameType.entrySet()) {
                        if (entry.getValue() == mapValue) {
                            String beanName = entry.getKey();
                            ObjectName objectName = registerBeanInstance(mapValue, beanKey);
                            replaceNotificationListenerBeanNameKeysIfNecessary(beanName, objectName);
                            return objectName;
                        }
                    }
                }
                return registerBeanInstance(mapValue, beanKey);
            }
        }
        catch (Exception ex) {
            throw new UnableToRegisterMBeanException(
                    "Unable to register MBean [" + mapValue + "] with key ‘" + beanKey + "‘", ex);
        }
    }

/**
     * Registers an existing MBean or an MBean adapter for a plain bean
     * with the {@code MBeanServer}.
     * @param bean the bean to register, either an MBean or a plain bean
     * @param beanKey the key associated with this bean in the beans map
     * @return the {@code ObjectName} under which the bean was registered
     * with the {@code MBeanServer}
     */
    private ObjectName registerBeanInstance(Object bean, String beanKey) throws JMException {
        ObjectName objectName = getObjectName(bean, beanKey);
        Object mbeanToExpose = null;
        if (isMBean(bean.getClass())) {
            mbeanToExpose = bean;
        }
        else {
            DynamicMBean adaptedBean = adaptMBeanIfPossible(bean);
            if (adaptedBean != null) {
                mbeanToExpose = adaptedBean;
            }
        }
        if (mbeanToExpose != null) {
            if (logger.isInfoEnabled()) {
                logger.info("Located MBean ‘" + beanKey + "‘: registering with JMX server as MBean [" +
                        objectName + "]");
            }
            doRegister(mbeanToExpose, objectName);
        }
        else {
            if (logger.isInfoEnabled()) {
                logger.info("Located managed bean ‘" + beanKey + "‘: registering with JMX server as MBean [" +
                        objectName + "]");
            }
            ModelMBean mbean = createAndConfigureMBean(bean, beanKey);
            doRegister(mbean, objectName);
            injectNotificationPublisherIfNecessary(bean, mbean, objectName);
        }
        return objectName;
    }

/**
     * Actually register the MBean with the server. The behavior when encountering
     * an existing MBean can be configured using the {@link #setRegistrationBehavior(int)}
     * and {@link #setRegistrationBehaviorName(String)} methods.
     * @param mbean the MBean instance
     * @param objectName the suggested ObjectName for the MBean
     * @throws JMException if the registration failed
     */
    protected void doRegister(Object mbean, ObjectName objectName) throws JMException {
        ObjectName actualObjectName;

        synchronized (this.registeredBeans) {
            ObjectInstance registeredBean = null;
            try {
                registeredBean = this.server.registerMBean(mbean, objectName);
            }
            catch (InstanceAlreadyExistsException ex) {
                if (this.registrationPolicy == RegistrationPolicy.IGNORE_EXISTING) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Ignoring existing MBean at [" + objectName + "]");
                    }
                }
                else if (this.registrationPolicy == RegistrationPolicy.REPLACE_EXISTING) {
                    try {
                        if (logger.isDebugEnabled()) {
                            logger.debug("Replacing existing MBean at [" + objectName + "]");
                        }
                        this.server.unregisterMBean(objectName);
                        registeredBean = this.server.registerMBean(mbean, objectName);
                    }
                    catch (InstanceNotFoundException ex2) {
                        logger.error("Unable to replace existing MBean at [" + objectName + "]", ex2);
                        throw ex;
                    }
                }
                else {
                    throw ex;
                }
            }

            // Track registration and notify listeners.
            actualObjectName = (registeredBean != null ? registeredBean.getObjectName() : null);
            if (actualObjectName == null) {
                actualObjectName = objectName;
            }
            this.registeredBeans.add(actualObjectName);
        }

        onRegister(actualObjectName, mbean);
    }

    /**
     * Called when an MBean is registered. Notifies all registered
     * {@link MBeanExporterListener MBeanExporterListeners} of the registration event.
     * <p>Please note that if an {@link MBeanExporterListener} throws a (runtime)
     * exception when notified, this will essentially interrupt the notification process
     * and any remaining listeners that have yet to be notified will not (obviously)
     * receive the {@link MBeanExporterListener#mbeanRegistered(javax.management.ObjectName)}
     * callback.
     * @param objectName the {@code ObjectName} of the registered MBean
     */
    @Override
    protected void onRegister(ObjectName objectName) {
        notifyListenersOfRegistration(objectName);
    }

    /**
     * Notifies all registered {@link MBeanExporterListener MBeanExporterListeners} of the
     * registration of the MBean identified by the supplied {@link ObjectName}.
     */
    private void notifyListenersOfRegistration(ObjectName objectName) {
        if (this.listeners != null) {
            for (MBeanExporterListener listener : this.listeners) {
                listener.mbeanRegistered(objectName);
            }
        }
    }

/**
 * A listener that allows application code to be notified when an MBean is
 * registered and unregistered via an {@link MBeanExporter}.
 *
 * @author Rob Harrop
 * @since 1.2.2
 * @see org.springframework.jmx.export.MBeanExporter#setListeners
 */
public interface MBeanExporterListener {

    /**
     * Called by {@link MBeanExporter} after an MBean has been <i>successfully</i>
     * registered with an {@link javax.management.MBeanServer}.
     * @param objectName the {@code ObjectName} of the registered MBean
     */
    void mbeanRegistered(ObjectName objectName);

    /**
     * Called by {@link MBeanExporter} after an MBean has been <i>successfully</i>
     * unregistered from an {@link javax.management.MBeanServer}.
     * @param objectName the {@code ObjectName} of the unregistered MBean
     */
    void mbeanUnregistered(ObjectName objectName);

}

<bean id="clientConnector"
        class="org.springframework.jmx.support.MBeanServerConnectionFactoryBean">
    <property name="serviceUrl" value="service:jmx:rmi://remotehost:9875"/>
</bean>

<bean id="proxy" class="org.springframework.jmx.access.MBeanProxyFactoryBean">
    <property name="objectName" value="bean:name=testBean"/>
    <property name="proxyInterface" value="org.springframework.jmx.IJmxTestBean"/>
    <property name="server" ref="clientConnector"/>
</bean>

/**
 * Creates a proxy to a managed resource running either locally or remotely.
 * The "proxyInterface" property defines the interface that the generated
 * proxy is supposed to implement. This interface should define methods and
 * properties that correspond to operations and attributes in the management
 * interface of the resource you wish to proxy.
 *
 * <p>There is no need for the managed resource to implement the proxy interface,
 * although you may find it convenient to do. It is not required that every
 * operation and attribute in the management interface is matched by a
 * corresponding property or method in the proxy interface.
 *
 * <p>Attempting to invoke or access any method or property on the proxy
 * interface that does not correspond to the management interface will lead
 * to an {@code InvalidInvocationException}.
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 1.2
 * @see MBeanClientInterceptor
 * @see InvalidInvocationException
 */

/**
     * Checks that the {@code proxyInterface} has been specified and then
     * generates the proxy for the target MBean.
     */
    @Override
    public void afterPropertiesSet() throws MBeanServerNotFoundException, MBeanInfoRetrievalException {
        super.afterPropertiesSet();

        if (this.proxyInterface == null) {
            this.proxyInterface = getManagementInterface();
            if (this.proxyInterface == null) {
                throw new IllegalArgumentException("Property ‘proxyInterface‘ or ‘managementInterface‘ is required");
            }
        }
        else {
            if (getManagementInterface() == null) {
                setManagementInterface(this.proxyInterface);
            }
        }
        this.mbeanProxy = new ProxyFactory(this.proxyInterface, this).getProxy(this.beanClassLoader);
    }

/**
 * {@link org.aopalliance.intercept.MethodInterceptor} that routes calls to an
 * MBean running on the supplied {@code MBeanServerConnection}.
 * Works for both local and remote {@code MBeanServerConnection}s.
 *
 * <p>By default, the {@code MBeanClientInterceptor} will connect to the
 * {@code MBeanServer} and cache MBean metadata at startup. This can
 * be undesirable when running against a remote {@code MBeanServer}
 * that may not be running when the application starts. Through setting the
 * {@link #setConnectOnStartup(boolean) connectOnStartup} property to "false",
 * you can defer this process until the first invocation against the proxy.
 *
 * <p>This functionality is usually used through {@link MBeanProxyFactoryBean}.
 * See the javadoc of that class for more information.
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 1.2
 * @see MBeanProxyFactoryBean
 * @see #setConnectOnStartup
 */

    /**
     * Prepares the {@code MBeanServerConnection} if the "connectOnStartup"
     * is turned on (which it is by default).
     */
    @Override
    public void afterPropertiesSet() {
        if (this.server != null && this.refreshOnConnectFailure) {
            throw new IllegalArgumentException("‘refreshOnConnectFailure‘ does not work when setting " +
                    "a ‘server‘ reference. Prefer ‘serviceUrl‘ etc instead.");
        }
        if (this.connectOnStartup) {
            prepare();
        }
    }

    /**
     * Ensures that an {@code MBeanServerConnection} is configured and attempts
     * to detect a local connection if one is not supplied.
     */
    public void prepare() {
        synchronized (this.preparationMonitor) {
            if (this.server != null) {
                this.serverToUse = this.server;
            }
            else {
                this.serverToUse = null;
                this.serverToUse = this.connector.connect(this.serviceUrl, this.environment, this.agentId);
            }
            this.invocationHandler = null;
            if (this.useStrictCasing) {
                // Use the JDK‘s own MBeanServerInvocationHandler,
                // in particular for native MXBean support on Java 6.
                if (JmxUtils.isMXBeanSupportAvailable()) {
                    this.invocationHandler =
                            new MBeanServerInvocationHandler(this.serverToUse, this.objectName,
                                    (this.managementInterface != null && JMX.isMXBeanInterface(this.managementInterface)));
                }
                else {
                    this.invocationHandler = new MBeanServerInvocationHandler(this.serverToUse, this.objectName);
                }
            }
            else {
                // Non-strict casing can only be achieved through custom
                // invocation handling. Only partial MXBean support available!
                retrieveMBeanInfo();
            }
        }
    }
    /**
     * Loads the management interface info for the configured MBean into the caches.
     * This information is used by the proxy when determining whether an invocation matches
     * a valid operation or attribute on the management interface of the managed resource.
     */
    private void retrieveMBeanInfo() throws MBeanInfoRetrievalException {
        try {
            MBeanInfo info = this.serverToUse.getMBeanInfo(this.objectName);

            MBeanAttributeInfo[] attributeInfo = info.getAttributes();
            this.allowedAttributes = new HashMap<String, MBeanAttributeInfo>(attributeInfo.length);
            for (MBeanAttributeInfo infoEle : attributeInfo) {
                this.allowedAttributes.put(infoEle.getName(), infoEle);
            }

            MBeanOperationInfo[] operationInfo = info.getOperations();
            this.allowedOperations = new HashMap<MethodCacheKey, MBeanOperationInfo>(operationInfo.length);
            for (MBeanOperationInfo infoEle : operationInfo) {
                Class<?>[] paramTypes = JmxUtils.parameterInfoToTypes(infoEle.getSignature(), this.beanClassLoader);
                this.allowedOperations.put(new MethodCacheKey(infoEle.getName(), paramTypes), infoEle);
            }
        }
        catch (ClassNotFoundException ex) {
            throw new MBeanInfoRetrievalException("Unable to locate class specified in method signature", ex);
        }
        catch (IntrospectionException ex) {
            throw new MBeanInfoRetrievalException("Unable to obtain MBean info for bean [" + this.objectName + "]", ex);
        }
        catch (InstanceNotFoundException ex) {
            // if we are this far this shouldn‘t happen, but...
            throw new MBeanInfoRetrievalException("Unable to obtain MBean info for bean [" + this.objectName +
                    "]: it is likely that this bean was unregistered during the proxy creation process",
                    ex);
        }
        catch (ReflectionException ex) {
            throw new MBeanInfoRetrievalException("Unable to read MBean info for bean [ " + this.objectName + "]", ex);
        }
        catch (IOException ex) {
            throw new MBeanInfoRetrievalException("An IOException occurred when communicating with the " +
                    "MBeanServer. It is likely that you are communicating with a remote MBeanServer. " +
                    "Check the inner exception for exact details.", ex);
        }
    }

/**
     * <p>Return a proxy that implements the given interface by
     * forwarding its methods through the given MBean server to the
     * named MBean.  As of 1.6, the methods {@link
     * JMX#newMBeanProxy(MBeanServerConnection, ObjectName, Class)} and
     * {@link JMX#newMBeanProxy(MBeanServerConnection, ObjectName, Class,
     * boolean)} are preferred to this method.</p>
     *
     * <p>This method is equivalent to {@link Proxy#newProxyInstance
     * Proxy.newProxyInstance}<code>(interfaceClass.getClassLoader(),
     * interfaces, handler)</code>.  Here <code>handler</code> is the
     * result of {@link #MBeanServerInvocationHandler new
     * MBeanServerInvocationHandler(connection, objectName)}, and
     * <code>interfaces</code> is an array that has one element if
     * <code>notificationBroadcaster</code> is false and two if it is
     * true.  The first element of <code>interfaces</code> is
     * <code>interfaceClass</code> and the second, if present, is
     * <code>NotificationEmitter.class</code>.
     *
     * @param connection the MBean server to forward to.
     * @param objectName the name of the MBean within
     * <code>connection</code> to forward to.
     * @param interfaceClass the management interface that the MBean
     * exports, which will also be implemented by the returned proxy.
     * @param notificationBroadcaster make the returned proxy
     * implement {@link NotificationEmitter} by forwarding its methods
     * via <code>connection</code>. A call to {@link
     * NotificationBroadcaster#addNotificationListener} on the proxy will
     * result in a call to {@link
     * MBeanServerConnection#addNotificationListener(ObjectName,
     * NotificationListener, NotificationFilter, Object)}, and likewise
     * for the other methods of {@link NotificationBroadcaster} and {@link
     * NotificationEmitter}.
     *
     * @param <T> allows the compiler to know that if the {@code
     * interfaceClass} parameter is {@code MyMBean.class}, for example,
     * then the return type is {@code MyMBean}.
     *
     * @return the new proxy instance.
     *
     * @see JMX#newMBeanProxy(MBeanServerConnection, ObjectName, Class)
     */
    public static <T> T newProxyInstance(MBeanServerConnection connection,
                     ObjectName objectName,
                     Class<T> interfaceClass,
                     boolean notificationBroadcaster) {
    final InvocationHandler handler =
        new MBeanServerInvocationHandler(connection, objectName);
    final Class[] interfaces;
    if (notificationBroadcaster) {
        interfaces =
        new Class[] {interfaceClass, NotificationEmitter.class};
    } else
        interfaces = new Class[] {interfaceClass};

    Object proxy =
        Proxy.newProxyInstance(interfaceClass.getClassLoader(),
                   interfaces,
                   handler);
    return interfaceClass.cast(proxy);
    }

    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        final Class methodClass = method.getDeclaringClass();

        if (methodClass.equals(NotificationBroadcaster.class)
            || methodClass.equals(NotificationEmitter.class))
            return invokeBroadcasterMethod(proxy, method, args);

        // local or not: equals, toString, hashCode
    if (shouldDoLocally(proxy, method))
            return doLocally(proxy, method, args);
        
        try {
            if (isMXBean) {
                MXBeanProxy p = findMXBeanProxy(methodClass);
                return p.invoke(connection, objectName, method, args);
            } else {
                final String methodName = method.getName();
                final Class[] paramTypes = method.getParameterTypes();
                final Class returnType = method.getReturnType();

                /* Inexplicably, InvocationHandler specifies that args is null
                   when the method takes no arguments rather than a
                   zero-length array.  */
                final int nargs = (args == null) ? 0 : args.length;

                if (methodName.startsWith("get")
                    && methodName.length() > 3
                    && nargs == 0
                    && !returnType.equals(Void.TYPE)) {
                    return connection.getAttribute(objectName,
                        methodName.substring(3));
                }

                if (methodName.startsWith("is")
                    && methodName.length() > 2
                    && nargs == 0
                    && (returnType.equals(Boolean.TYPE)
                    || returnType.equals(Boolean.class))) {
                    return connection.getAttribute(objectName,
                        methodName.substring(2));
                }

                if (methodName.startsWith("set")
                    && methodName.length() > 3
                    && nargs == 1
                    && returnType.equals(Void.TYPE)) {
                    Attribute attr = new Attribute(methodName.substring(3), args[0]);
                    connection.setAttribute(objectName, attr);
                    return null;
                }

                final String[] signature = new String[paramTypes.length];
                for (int i = 0; i < paramTypes.length; i++)
                    signature[i] = paramTypes[i].getName();
                return connection.invoke(objectName, methodName,
                                         args, signature);
            }
        } catch (MBeanException e) {
            throw e.getTargetException();
        } catch (RuntimeMBeanException re) {
            throw re.getTargetException();
        } catch (RuntimeErrorException rre) {
            throw rre.getTargetError();
        }
        /* The invoke may fail because it can‘t get to the MBean, with
           one of the these exceptions declared by
           MBeanServerConnection.invoke:
           - RemoteException: can‘t talk to MBeanServer;
           - InstanceNotFoundException: objectName is not registered;
           - ReflectionException: objectName is registered but does not
             have the method being invoked.
           In all of these cases, the exception will be wrapped by the
           proxy mechanism in an UndeclaredThrowableException unless
           it happens to be declared in the "throws" clause of the
           method being invoked on the proxy.
         */
    }