Implementing DynamicMBean interface Introduction Using JMX (Java Management eXtensions) to manage part of your application is a great java feature. The standard Mbeans mechanisms which consist of creating a classwhich implements an MBean interface is quite simple and already allows to manage most of your application. In this article, I will describe how can we implements the DynamicMBean interface to do more 'complex' things. Especially, we will look on how we can we expose and modify a set of properties, and how can we expose methods by specifiing their names (The java code will be more clear than my poor english). The following examples are taken from the work I have done on the PEtALS CDK (Component Development Kit) in order to expose a set of JBI extensions and bootstrap methods for management. How to expose a set of properties? The standards MBeans automatically expose the setters and getters methods as MBean attributes. Imagine that you have a set of properties (a HashMap/Properties...). How can you manage this object, how can you change a value in the set? Simply by creating an implementation of the DynamicMBean interface. The following code snippet shows how we can do such a thing. /* * (non-Javadoc) * * @see javax.management.DynamicMBean#getAttribute(java.lang.String) */ public synchronized Object getAttribute(String attribute) throws AttributeNotFoundException, MBeanException, ReflectionException { String value = managedBootstrap.getComponentPropertiesManager() .getProperties().getProperty(attribute); if (value != null && !value .startsWith(ComponentPropertiesManager.MANAGED_METHOD_PREFIX)) { return value; } else { throw new AttributeNotFoundException("Attribute '" + attribute + "' does not exists");
Transcript
Implementing DynamicMBean interface
Introduction
Using JMX (Java Management eXtensions) to manage part of your application is a great java feature. The standard Mbeans mechanisms which consist of creating a class which implements an MBean interface is quite simple and already allows to manage most of your application.In this article, I will describe how can we implements the DynamicMBean interface to do more 'complex' things. Especially, we will look on how we can we expose and modify a set of properties, and how can we expose methods by specifiing their names (The java code will be more clear than my poor english).
The following examples are taken from the work I have done on the PEtALS CDK (Component Development Kit) in order to expose a set of JBI extensions and bootstrap methods for management.
How to expose a set of properties?
The standards MBeans automatically expose the setters and getters methods as MBean attributes. Imagine that you have a set of properties (a HashMap/Properties...). How can you manage this object, how can you change a value in the set? Simply by creating an implementation of the DynamicMBean interface.
The following code snippet shows how we can do such a thing.
The previous methods are the ones which are called by the JMX implementation for management. In our case it is quite simple since a property entry is directly mapped into an attribute...
Note 1 : The managedBootstrap attribute is a class which contains a Properties object.Note 2 : We persist the properties in a file each time a property is modified.
In order to expose these attributes, we will see later that we need to create a set of MBeanAttributeInfo that will be used by the getMBeanInfo method to create the information object used by JMX to expose all of this.
/**
* Dynamically get attributes for the MBean. The attributes are the ones
MBeanAttributeInfo[] attrs = new MBeanAttributeInfo[attributeKeys
.size()];
Iterator<String> it = attributeKeys.iterator();
for (int i = 0; i < attrs.length; i++) {
String name = it.next();
attrs[i] = new MBeanAttributeInfo(name, "java.lang.String",
"Property " + name, true, true, false);
}
return attrs;
}
How to expose a set of methods?
Building the MBeanInfo
In the previous chapter, I have introduced how we can dynamically expose properties. Now we will focus on how we can choose the methods to expose through JMX. There are several methods to do this. Here I have choosen to expose only the public methods that are programatically defined in a list. I have choosen this simple way to allow the component developer to simply define the methods he wants to expose by returning a list of methods names... Simple and efficient!
/**
* Dynamically get the operations for the MBean. The operations are defined
* in the properties manager with a special prefix.
result = new MBeanOperationInfo[operations.size()];
operations.toArray(result);
return result;
}
This time again, we are are creating a set of MBeanOperationInfo from a list methods names. We retrieve the methods from the class we want to manage from the managedBootstrap class by reflection.
This method will be then used to create the MBeanInfo that is returned by the method getMBeanInfo:
I am a software engineer and community manager on the open source PEtALS ESB project at eBM WebSourcing.You can get this article as PDF file on my scribd space or on my work blog.
