Saturday, October 27, 2007

 

Standard MBeans and Documentation

This blog-post assumes that you are a Java Programmer and have used or at least have knowledge of JMX technology. If word JMX is not ringing the bell, and if you are a Java programmer, I strongly suggest you get to know this technology and I'm sure you won't regret that you did. Go here for more info.

JMX technology in Java ecosystem has been playing tremendous role in making the Java components more manageable and maintainable. If you are developing a Java component and are exposing the configuration/management through set of attributes/operations, most probably you would be using

Back to point. If you are using standard MBeans with an interface defining all attributes/operations and an implementation class to provide the functionality, I'm sure you would have noticed that attributes/operations on the JMX agents are not being displayed but just empty.

One would have put in enough effort to document the MBeans interface with all nitty-gritty details but it is would be of no use if it is not being displayed in the JMX agent view.  This is due to fact that JMX  agents are accessing your interfaces at runtime, by then Java compiler would have removed all javadocs and changed the parameter names for operations. However StandardMBeans provide set of hooks, which can show the appropriate documentation on the agent view.

Documentation hooks works by set of getDescription/getParameter methods on StandardMBean class before constructing the MBeanInfo object for your MBean.  Where you can override those method to provide the documentation appropriate for your MBean, which would displayed on the agent view. However it is required to copy the documentation from MBean interface javadocs and programmatically return it. It is laborious and unmaintainable.  Solution being, generate that class which can generate the documentation automatically from the MBean interface javadocs.

To my surprise I didn't find any tool/utility which can generate this java file automatically from the MBean interface and provides the documentation at runtime. So I decided to implement my own and release to public. It is MBeanDoclet.

MBeanDoclet automatically generates a java source file for set of MBeans and provides the same javadoc documentation at runtime. So if you modified the javadoc, it is automatically updated in JMX Agents.

Example worth ten-thousand words. So here is one. For ex., if we have a MBean named TestMBean with some nicely written documentation

package com.brsanthu.mbeandoclet;

/**
 * MBean created to demonstrate the MBean Doclet usage.
 */
public interface TestMBean {
   
    /**
     * This is standard mbean attribute, which does nothing
     * but used only to demonstrate the MBeanDoclet usage.
     */
    public int getSampleAttribute();
   
    /**
     * This is standard mbean operation, which does nothing
     * but used only to demonstrate the MBeanDoclet usage.
     */
    public void sampleOperation();
}
Java2html

Running the MBeanDoclet, generates the following file.

////////////////////////////////////////////////////////////////////////////
//
// CAUTION: This source file is automatically generated by MBeanDoclet.
//          Any modifications would be overwritten nexttime it runs.
//
////////////////////////////////////////////////////////////////////////////

package com.brsanthu.mbeandoclet;

import javax.management.MBeanAttributeInfo;
import javax.management.MBeanInfo;
import javax.management.MBeanOperationInfo;
import javax.management.MBeanParameterInfo;
import javax.management.NotCompliantMBeanException;
import javax.management.StandardMBean;

public class TestMBeanJavadoc extends StandardMBean {

    public TestMBeanJavadoc(Class mbeanInterface) throws NotCompliantMBeanException {
        super(mbeanInterface);
    }

    public TestMBeanJavadoc(Object implementation, Class mbeanInterface)
                    throws NotCompliantMBeanException {
        super(implementation, mbeanInterface);
    }

    @Override
    protected String getDescription(MBeanInfo info) {
    String description = "";

        description = "MBean created to demonstrate the MBean Doclet usage.";

        return description;
    }

    @Override
    protected String getDescription(MBeanAttributeInfo info) {

        String description = "";

        if (false) {
            //This is always false stmt is added to make easier
            //to generate following blocks of else condition.
     

        } else if (info.getName().equals("SampleAttribute")) {
            description = "This is standard mbean attribute, which does nothing" +
 " but used only to demonstrate the MBeanDoclet usage.";


        } else {
          description = super.getDescription(info);
        }

        return description;
    }

    @Override
    protected String getDescription(MBeanOperationInfo info) {
        String description = "";

        if (false) {
            //This is always false statement is added just to make it easier
            //to generate following multiple blocks of else conditions.


        } else if (info.getName().equals("sampleOperation")) {
            description = "This is standard mbean operation, which does nothing" +
 " but used only to demonstrate the MBeanDoclet usage.";


        } else {
          description = super.getDescription(info);
        }

        return description;
    }
}
Java2html

This automatic generated has added lots of value-add to the MBean we have been developing.

If this doclet can be of any useful, you can download here. If you have any questions/issues, mail be brsanthu[at]yahoo[dot]com.


# posted by Santhosh @ 1:09 PM 3 comments

Sunday, October 21, 2007

 

Poor Comcast Customer Service

A 70 year old woman from Bristow, VA took extreme measure to vent out the frustration of poor service from Comcast and went on to Hammer down the Comcat's office equipments. Well, I don't support her action of hammering down, Cable company should learn something from this to improve the service.

Read more here.


# posted by Santhosh @ 12:38 PM 0 comments

Saturday, October 06, 2007

 

Best of Adnan Sami

Do you like Adnan Sami's pop songs? Here is the You Tube play list of all his good songs. Enjoy!


# posted by Santhosh @ 9:04 PM 0 comments

Wednesday, October 03, 2007

 

Java Substring Caveat

It is one of the commonly used function in the java String class but many people don't realize the caveat associated with it.

When you call the substring on a String object, the implementation do NOT create a new char array that is backing it but shares it.  Most of the cases this does work fine except in scenarios where you have a very large original String and want to keep reference to a part of that String.

For ex.,

        String originalString = "Very large string to demo the caveat with substring";
        String newString = originalString.substring(42);
Java2html

Programmer would assume that newString has occupies memory to store 9 characters but truth is that it is 51 characters.  This is due to the fact that when substring is called, Java String library didn't actually create a new character array of required length but used the same one created by originalString.  This isn't an issue if you continue to keep the strong reference to the originalString as newString still does share same memory space but otherwise newString is using more memory than it should.

Is there a simple solution? There is.

String newString = new String(originalString.substring(42));
Java2html
 
This instructs Java library to create a new character array of just required length and initialize.
 
Happy (Java) coding!

# posted by Santhosh @ 5:39 PM 0 comments

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