Open Mbeans Tutorial

Writing an MBean in java is very simple. But, when you want the return type to a table of data(say, some metrics) then simple Mbeans are not of much use. One way to get table of data as a return type is using a Open Mbeans. This tutorial gives a simple example of how to write an Open Mbean that returns Table of data.

Step 1: Define a dynamic MXBean by implementing interface "DynamicMBean".

public class QuoteMXBean implements DynamicMBean { 
    public Object getAttribute(String attribute) throws AttributeNotFoundException, 
        MBeanException, ReflectionException{ 
        //TODO 
    } 
    public void setAttribute(Attribute attribute) throws AttributeNotFoundException, 
        InvalidAttributeValueException, MBeanException, ReflectionException{ 
        //TODO 
    } 
    public AttributeList getAttributes(String[] attributes){ 
        //TODO    
    } 
    public AttributeList setAttributes(AttributeList attributes){ 
        //TODO    
    } 
    public Object invoke(String actionName, Object params[], String signature[]) 
        throws MBeanException, ReflectionException{ 
        //TODO 
    } 
    public MBeanInfo getMBeanInfo(){ 
        //TODO 
    } 
} 

Step 2:
A table is made up of rows. And each row is made up of columns. We will have to give exactly this description defining a table.

String[] itemNames = { "symbol", "localTimeStamp", "latestResponse"}; 
String[] itemDescriptions = { "Symbol", 
            "The Timestamp for the response as on server", "The response String from Quoteserver"}; 
OpenType[] itemTypes = { SimpleType.STRING, 
            SimpleType.STRING, SimpleType.STRING};            
CompositeType snapshotType = new CompositeType("snapshot", "Quote Data", 
                itemNames, itemDescriptions, itemTypes);

All the variables can be made private and initialized either in a static block or in the constructor. The CompositeType just defined that each row will contain the columns "symbol", "localTimeStamp", "latestResponse". Now lets define the table type it self.

String[] index = { "symbol" }; 
TabularType quoteTableType = new TabularType("quoteSnapshots", 
                    "List of Quotes", snapshotType, 
                    index);

That is, a table type "quoteTableType" is a collection of rows given by Composite type "snapshotType". The "index" gives, the unique identification for the table.


Step 3:
Lets declare the table with type "quoteTableType".

private TabularDataSupport quoteSnapshot = new TabularDataSupport(quoteTableType); 

Please add the getter and setters for the same.


Step 4:
Lets implement getMBeanInfo().

OpenMBeanInfoSupport info; 
    OpenMBeanAttributeInfoSupport[] attributes = new OpenMBeanAttributeInfoSupport[1]; 
    OpenMBeanConstructorInfoSupport[] constructors = new OpenMBeanConstructorInfoSupport[1]; 
        OpenMBeanOperationInfoSupport[] operations = new OpenMBeanOperationInfoSupport[4]; 
        MBeanNotificationInfo[] notifications = new MBeanNotificationInfo[0]; 

//Just one attribute 
     attributes[0] = new OpenMBeanAttributeInfoSupport("QuoteSnapshot", 
                "Table of quotes data", quoteSnapshotType, true, false, 
                false); 
//No arg constructor                
         constructors[0] = new OpenMBeanConstructorInfoSupport( 
                        "QuoteMXBean", 
                        "Constructs a QuoteMXBean instance.", 
                new OpenMBeanParameterInfoSupport[0]); 

//Just one operation 

    OpenMBeanParameterInfo[] params = new OpenMBeanParameterInfoSupport[0]; 
        operations[0] = new OpenMBeanOperationInfoSupport( 
                "resetAndGetQuoteSnapshot", 
                "Reset and get the latest available data for the Quotes", 
                params, quoteSnapshotType, 
                MBeanOperationInfo.INFO); 
//Build the info 

    info = new OpenMBeanInfoSupport(this .getClass().getName(), 
                "Quote - Open - MBean", attributes, constructors, 
                operations, notifications);    

Step 5:
Implement getAttribute() and getAttributes().

 public Object getAttribute(String attributeName) throws AttributeNotFoundException, 
            MBeanException, ReflectionException { 
        if (attributeName.equals("QuoteSnapshot")) { 
                return (TabularData)getQuoteSnapshot(); 
            } 
        throw new AttributeNotFoundException("Cannot find " 
                + attributeName + " attribute "); 
    } 
    public AttributeList getAttributes(String[] attributeNames) { 
            AttributeList resultList = new AttributeList(); 
            if (attributeNames.length == 0) 
                return resultList; 
            for (int i = 0; i < attributeNames.length; i++) { 
                try { 
                    Object value = getAttribute(attributeNames[i]); 
                    resultList.add(new Attribute(attributeNames[i], value)); 
                } catch (Exception e) { 
                    e.printStackTrace(); 
                } 
            } 
            return (resultList); 
    }

Step 6:
Implement setAttribute().
There is nothing to set in this example.

    public void setAttribute(Attribute arg0) throws AttributeNotFoundException, 
            InvalidAttributeValueException, MBeanException, ReflectionException { 
        throw new AttributeNotFoundException( 
        "No attribute can be set in this MBean"); 
    } 

    @Override 
    public AttributeList setAttributes(AttributeList arg0) { 
        return new AttributeList(); 
    }

Step 7:
Implement invoke().

public Object invoke(String operationName, Object[] params, String[] signature) 
            throws MBeanException, ReflectionException { 
        if (operationName.equals("resetAndGetQuoteSnapshot")) { 
            try { 
                return buildSnapshot(); //This is where you delegate the invokation to your original method. 
            } catch (OpenDataException e) { 
                throw new MBeanException(e, "invoking resetAndGetQuoteSnapshot: " 
                        + e.getClass().getName() + "caught [" 
                        + e.getMessage() + "]"); 
            } 
        } 
        else{ 
            throw new ReflectionException(new NoSuchMethodException( 
                    operationName), "Cannot find the operation " 
                    + operationName); 
        } 
    } 
    public Object buildSnapshot() throws OpenDataException { 
            quoteSnapshot = new TabularDataSupport(quoteTableType); 
            SomeVo vo = //get the data 
            Object[] itemValues = { vo.symbol, vo.localDate, vo.response}; 
            CompositeData result = new CompositeDataSupport(snapshotType, 
                    itemNames, itemValues); 
                    quoteSnapshot.put(result); 
            return quoteSnapshot; 
    }

This is all is needed to build an Open MBean that supports a Tabular data as output. You can use jconsole and view the output. Obviously, you have to deploy the MBean in mbean server. I use spring to do that job. The spring XML is given below.

<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter" lazy-init="false"> 
        <property name="beans"> 
          <map> 
            <entry key="com.ssb.mbean:type=QuoteMXBean" value-ref="quoteMXBean"/> 
          </map> 
        </property> 
     </bean> 
    <bean id="quoteMXBean" class="com.ssb.mbean.QuoteMXBean"/> 
    <bean id="registry" class="org.springframework.remoting.rmi.RmiRegistryFactoryBean" 
         p:port="9999" /> 
    <bean id="serverConnector" class="org.springframework.jmx.support.ConnectorServerFactoryBean" 
         p:objectName="connector:name=rmi" 
         p:serviceUrl="service:jmx:rmi://localhost/jndi/rmi://localhost:9999/quotesconnector" 
         p:threaded="true" 
         p:daemon="true"/>

The above example is trying to display the latest quote data that is available to the system.