Extending OpenNMS

The OpenNMS installation directory contains etc/ directory which contains all kind of configuration files which require to run openNMS, it has various configuration files for each daemon module, for example for capability daemon there is capsd.xml for collector daemon it has capsd.xml and for dataCollection definition it has jmx-dataCollection.xml for Mbeans definition, similarity for snmp there is dataCollection.xml for defining what OID’s need to be collected for SNMP services.

Now this etc directory also contains service-configuration.xml which has all module definition plus which method to be invoked for loading the module. These modules can be daemon or non daemon depending upon the requirement. all module follows standard MBean criteria. These modules are started in the sequence they are mention in the file. I mean top most will be executed first and the bottom most ( which is embedded jetty-web server) will be the last.

 

<service-configuration>
  <service>
    <name>:Name=XSLTProcessor</name>
    <class-name>mx4j.tools.adaptor.http.XSLTProcessor</class-name>
  </service>
  <service>
    <name>:Name=HttpAdaptor</name>
    <class-name>mx4j.tools.adaptor.http.HttpAdaptor</class-name>
    <attribute>
      <name>Port</name>
      <value type="java.lang.Integer">8180</value>
    </attribute>
    <attribute>
      <name>Host</name>
…………………………………….

If we add new service definition here, the OpenNMS will load our service ..

for example let say we want to delete all logs or previous data collected on starting up openNMS, we have to add our service in this xml then only openNMS could start our service.

<service-configuration>

<service>
  <name>OurService:Name=CleanupService</name>
  <class-name>org.ourservice.Clean</class-name>
  <invoke at="start" pass="0" method="start"/>

</service>
  <service>
    <name>:Name=XSLTProcessor</name>
    <class-name>mx4j.tools.adaptor.http.XSLTProcessor</class-name>
  </service>
  <service>
    <name>:Name=HttpAdaptor</name>
    <class-name>mx4j.tools.adaptor.http.HttpAdaptor</class-name>
    <attribute>
      <name>Port</name>
      <value type="java.lang.Integer">8180</value>
    </attribute>
    <attribute>
      <name>Host</name>

now CleanupService will be triggered first. for starting this service start method will be invoked of Clean class. The clean Class must implement MBean.
create CleanMBean interface and declare start method signature.

package org.ourservice;

public interface CleanMBean {
    public void start();
}

now create Clean class and implement CleanMBean interface, also implement logic to clean the data.

package org.ourservice;

public class Clean implements CleanMBean {
    public void start(){
       System.out.println(“Cleaned all”);

     }

}

 

 

After compiling the Clean class and other dependant classes. create classes directory inside openNMS installation directory and put all our classes inside. then start openNMS.

Java5 Instumentation API

The instrumentation API is for run time byte manupulation, or you can say bytecode engineering. 

we have to define our instrumentation agent which consist starting point same as main method of any java application with different arguments.

String : arguments to this agent..

Instrumentation object, instrumentation agent is a class with a special method, with a predefined signature, that the JVM will invoke before the rest of the application for you to set up any instrumentation code. Generally, instrumentation is the act of transforming classes for profiling purposes: for example, an interesting feature provided by the instrumentation framework is the ability to measure the memory usage of an object. 
 

import java.lang.instrument.Instrumentation;

public class MyAgent {
    public static void premain(String agentArguments,
            Instrumentation instrumentation) {

        MyTransFormer transformer = new MyTransFormer();
        instrumentation.addTransformer(transformer);
        Node node = new Node();
        long size = instrumentation.getObjectSize(node);
        System.out.println("size of "+ node.getClass().getSimpleName() + size);
    }
}

we have compiled the agent class and  we need to package it into a jar , we also need to create a manifest file

Premain-Class: MyAgent 

java -javaagent:myagent.jar TestMain

creating transformer

import java.lang.instrument.ClassFileTransformer; 
import java.security.ProtectionDomain; 

public class MyTransFormer implements ClassFileTransformer {

    public MyTransFormer() {
        super();
    }

public byte[] transform(ClassLoader loader, String className,
            Class redefiningClass, ProtectionDomain domain, byte[] bytes) {
        // some changes in byte code // there are some standard API for byte
        // code modification exp: BCEL, ASM etc…
        return bytes;
    }
}

There are some links i went while reading .

1. http://www.javalobby.org/java/forums/t19309.html#92037417


2. http://www.cs.nuim.ie/~jpower/Research/instrument/#examples


3. http://www.javamex.com/tutorials/memory/instrumentation.shtml

Handling more than one exception, Java SE 7 new feature.

In Java SE 7 and later, a single catch block can handle 
more than one type of exception. This feature can reduce code 
duplication and lessen the temptation to catch an overly broad 
exception. 

consider the following example... 

try{
.............

}

catch (IOException ex) {
     logger.log(ex);
     throw ex;
catch (SQLException ex) {
     logger.log(ex);
     throw ex;
}

The following example, which is valid in Java SE 7 and later, 

eliminates the duplicated code:

catch (IOException|SQLException ex) {
    logger.log(ex);
    throw ex;
} 

Installing openNMS on RedHat using rpm.

I am assuming postgres database is already installed.

download the following rpm.

• openNMS core :
  opennms-core-1.8.5-1.noarch.rpm
•  jetty for opennms :
  opennms-webapp-jetty-1.8.5-1.noarch.rpm 
• Jicmp  from here depending upon the the architecture. for example :
  (jicmp-1.0.6-1.fc8.i386.rpm)
  http://rpmfind.net/linux/rpm2html/search.php?query=jicmp&submit=Search+...&system=&arch=

 now installing process...
rpm -ivh opennms-core-1.8.5-1.noarch.rpm
rpm -ivh  jicmp-1.0.6-1.fc8.i386.rpm
rpm -ivh opennms-webapp-jetty-1.8.5-1.noarch.rpm


stop postgres database if it is running
/etc/init.d/postgresql stop

To allow OpenNMS to connect to the database, you will need to edit your database's  
pg_hba.conf file. On many default installations it can be found in the directory
/var/lib/pgsql/data/

local   all   all                      ident sameuser
host    all   all    127.0.0.1/32      ident sameuser
host    all   all    ::1/128           ident sameuser

You will need to change these entries to resemble the following: 

local   all   all                      trust

host    all   all    127.0.0.1/32      trust

host    all   all    ::1/128           trust

Next, you will need to edit postgresql.conf to accept TCP/IP 

connections. As with pg_hba.conf, check the defaults or your 

distribution's PostgreSQL documentation for the location of 

this file. As before, on many default installations it can 

be found in the directory /var/lib/pgsql/data/ Both 

postgresql.conf and pg_hba.conf by default should be 

in the same location.

....

#listen_addresses = 'localhost'

 ....

uncomment this line to resemble

....

listen_addresses = 'localhost'

 ....

start the postgres db..
/etc/init.d/postgresql start


go to /opt/opennms/bin/ (default installation dir for opennms)

run the install script...
#>install



after that start opennms

#>opennms start

open http://localhost:8980/opennms/index.jsp

and enjoy...:)

IIT-BHU-Anamika

Simulating queue using stack...

Problem statement: we are given one stack and we have to implement the queue using this stack means enqueue(insert into stack) and dequeue ( pop from stack) should behave as queue. No additional stack should be used.

This can be done using Operating system stack by using recursion.

public class SimulatedQueue < E > {
    private java.util.Stack < E > stack = 
                     new java.util.Stack < E >();

    public void insert(E elem) {
        if (!stack.empty()) {
            E topElem = stack.pop();
            insert(elem);
            stack.push(topElem);
        }
        else
            stack.push(elem);
    }

    public E remove() {
        return stack.pop();
    }
}