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Java IoT: Article

Integrating AJAX with the JMX Notification Framework

Opposite Ends of the Systems Management Stack

Each step is described in detail below.

Register MBeans and MBean Listeners
On each J2EE server instance, two start-up classes are run at server start-up:

  • ManagementStartup: Registers the UserWeb MBean in the local MBean server. Startup class parameters include default settings of the alert status, as well as the MBean name and MBean class. For example:

    <StartupClass
       Arguments="ServerName=admin,
         MBeanName=ExampleApp:Name=UserWeb,
         MBeanClass=com.grahamh.management.userWeb.UserWeb"
         ClassName="com.grahamh.management.startup.ManagementStartup"
       FailureIsFatal="true" Name="UserWEB" Notes=""
       Targets="admin,OLTPCluster"/>

  • MbeanRegistrations: Used to register a Singleton POJO, ManagementListener, with the UserWeb MBean on the administration server.

    A javax.management.NotificationFilterSupport object is used to list the notification types that the UserWeb MBean will generate and the listener will receive:

    // MbeanRegistrations.java
    MBeanHelperFactory.getWebHelper().registerListener();

    // UserWebMbeanListener.java
    public void registerListener() throws UserWebException{

    try {
    // get listener and filter
    ManagementListener listener = MBeanHelperFactory.getListener();
    NotificationFilterSupport filter = listener.getSupportedEvents();

    // get admin mbean server;
    //register the listener and filter with the UserWeb MBean
    RemoteMBeanServer rmbs = getAdminMbeanServer();
    rmbs.addNotificationListener
    ("ExampleApp:Name=UserWeb", listener, filter, null);
    }
    catch (Exception e) {
    throw new UserWebException
    ("Unable to registerListener: "+ e.getMessage(), e);
    }
    }

    The listener.getSupportedEvents() method returns the following filter:

    NotificationFilterSupport filter = new NotificationFilterSupport();
    filter.enableType("alert.broadcast");

When ManagementListener is run at server start-up, a connection is made to the MBean server on the (remote) administration server and the (local) ManagementListener is registered as a listener on events generated by the UserWeb MBean, with a filter set to "alert.broadcast" event types.

Because the ManagementListener implements Weblogic.management.RemoteNotificationListener, it can get JMX notifications that are generated in either the local JVM or a remote JVM; in this case, generated in the remote administration server JVM.

Broadcast Admin MBean properties
The administration and managed UserWeb MBeans can be set independently, giving any one J2EE server a localized AJAX response. However, a general Operations, Administration & Support (OA&M) support pattern would set the admin MBean properties and then broadcast these properties to the MBeans on the remote application servers, using the Notification model, for subsequent AJAX retrieval.

Because the UserWeb MBean is based on ApplicationMBean, which extends javax.management.NotificationBroadcasterSupport, the infrastructure is in place for the UserWeb MBean to notify all listeners. Hence, the administrator sets the relevant MBean properties (using the HTMLAdaptor) and clicks BroadcastState (see Figure 2).

Consequently, the UserWeb.broadcastState()method is executed, which notifies all listeners synchronously with the state of the admin MBean:

public void broadcastState() throws Exception {
try {
Notification n = new Notification
("alert.broadcast", "ExampleApp:Name=UserWeb", 0);
n.setUserData(new UserWeb(this));
this.sendNotification(n);
}
catch (Exception e) {
throw e;
}
}

Because the data is serialized over the network, the non-transient object graph must be serializable.

Receive Notification of MBean Props via Listener
The event listener is the ManagementListener Singleton. The JMX Notification framework on the administration server makes a remote call to the ManagementListener handleNotification() method in each listener on each of the OLTP cluster JVMs, which registered on server start-up:

public void handleNotification(Notification notification, Object handback) {
System.out.println("Received alert: " + notification.getType());

// get event userdata from notification
Object userData = notification.getUserData();

if (userData instanceof UserWeb) {
// comes from destin8 Web
UserWeb WebVo = (UserWeb)userData;
UserWebMBeanHelper helper = MBeanHelperFactory.getWebHelper();

// get from value object and set into local MBean using
MBeanHelper
helper.setAlertMessage(WebVo.getAlertMessage());
helper.setAlertStatus(WebVo.getAlertStatus());
helper.setCallBack(WebVo.getCallBack());
helper.setRefreshAlertStatus(WebVo.getRefreshAlertStatus());
}
}

The 'master' UserWeb data is set into the local User-Web MBean via its MBean helper. Consequently each managed server is updated with the master UserWeb state.

That's as far as the JMX elements need to go.

AJAX Request of Management State
The browser client is AJAX-enabled as follows:

  • main.jsp - instrumented JSP page that checks the (JMX) alert status and polls the server for alerts. It includes admin.js
  • admin.js - JavaScript utilities that use XMLHttpRequest to poll the server for the management state, parse the XML response, and repaint the 'status' area of the screen
JavaScript (described below) is included in main.jsp as follows:

<script type="text/javascript" src="./js/admin.js" ></script>

Rather than poll continuously, we will only poll if alerting is enabled. We use the UserWebMBeanHelper to check this status. If enabled, the JavaScript function initAdmin() is invoked when the page loads:

<%
if (MBeanHelperFactory.getWebHelper().isAlertEnabled()) {
%>
<body bgcolor="#F4FFE4" onload="initAdmin();">
<%
} else {
%>
<body bgcolor="#F4FFE4">
<%
}
%>

More Stories By Graham P. Harrison

Previously a Senior Consultant with BEA, Graham is the author of Dynamic Web Programming using Java (Prentice Hall, 2000) in addition to a number of articles for the Java Developers Journal and IBM DeveloperWorks. He has a focus on Enterprise Architecture, Performance Tuning and Capacity Planning

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