Skip to main content

Simple tutorial about complex OSGI framework

What is OSGI?

If you are in the software industry, you might have heard the term OSGI. But most probably you might not heard about this. That does not mean that you don't need to know about it. OK. What really OSGI is?

OSGI stands for Open Services Gateway Initiative. But that does not tell about it (That's the way most of the definitions are :D). It is a  Dynamic Module System for Java, which


  • defines an architecture for modular application development.
  • It allows you to break your application into multiple modules and thus more easily manage cross-dependencies between them.

 Why you need OSGI?

From a developer's perspective, OSGi offers the following advantages:
  • You can install, uninstall, start, and stop different modules of your application dynamically without restarting the container.
  • Your application can have more than one version of a particular module running at the same time.
  • OSGi provides very good infrastructure for developing service-oriented applications, as well as embedded, mobile, and rich internet apps.
Given that you use servlet containers for building Web applications and EJB containers for building transactional applications, you may be wondering why you need yet another type of container. The short answer is that OSGi containers are intended specifically for developing complex Java applications that you want to break up into modules.

How OSGI works?                    

Similar to the Java Servlet and EJB specifications, the OSGi specification defines two things:


  • a set of services that an OSGi container must implement 
  • a contract between the container and your application. 


Developing on the OSGi platform means first building your application using OSGi APIs, then deploying it in an OSGi container

How to benefit from OSGI?

 If you are a developer in the enterprise application domain, the OSGi container has such a low footprint that you can easily embed it into an enterprise application. For example, let's say you're developing a complex Web application. You want to break the application into multiple modules: one module for the view layer, another for the DAO layer, and a third module for the data access layer. Using an embedded OSGi container to manage the cross-dependencies of these modules would enable you to update your DAO layer (say from slow DAO to fast DAO) without restarting your application.
As long as your application is compliant with the OSGi specification it should be able to run in any OSGi-compliant container. Currently, there are three popular open source OSGi containers:

  • Equinox is the reference implementation for the framework portion of the OSGi Service Platform Release 4. It is the modular Java runtime at the heart of the Eclipse IDE, and implements all of the mandatory and most of the optional features of the OSGi R4 specification.
  • Knopflerfish is an open source implementation of the OSGi R3 and OSGi R4 specifications. Knopflerfish 2 implements all the mandatory features and some of the optional features defined in the R4 specification.
  • Apache Felix is the open source OSGi container from the Apache Software Foundation. At the time of writing this container is not fully compliant with the OSGI R4 specification.

Looks like this is getting a bit complex. I will stop here and compile another tutorial on developing a sample OSGI application.
Labels:

Comments

Post a Comment

Popular posts from this blog

How to protect your APIs with self contained access token (JWT) using WSO2 API Manager and WSO2 Identity Server

In a typical enterprise information system, there is a high chance that people will use different types of systems built by different vendors to implement certain types of functionalities. The APIs might be hosted in an API Manager developed by vendor A and the user management can be implemented using a different vendor (vendor B). In this type of a situation, one system will not be able to directly contact the other system but they want to use both systems in tandem. Self-contained access tokens are used in these types of situations where applications can get the token from one system and use that in another system to access protected resources. In this scenario, the second system does not need to make a contact to the first system over the network to validate the user information since the token is self-contained and it has relevant details about the user. This will improve the token processing time significantly since it completely removes the network interaction. The below fig...
1 comment
Read more

WSO2 ESB creating a response for a "GET" request

When you are creating REST APIs with WSO2 ESB, you may need to send some response message back to the user when something goes wrong. In this kind of scenario, you can create a payload inside the ESB and send it back. For doing this, you can use the below configuration. <api xmlns=" http://ws.apache.org/ ns/synapse " name="LoopBackProxy" context="/loopback">    <resource methods="POST GET">       <inSequence>          <property name="NO_ENTITY_BODY" scope="axis2" action="remove"></property>          <log level="full"></log>          <payloadFactory media-type="xml">             <format>                <m:messageBeforeLoopBack xmlns:m=" http://services...
Post a Comment
Read more

How to configure timeouts in WSO2 ESB to get rid of client timeout errors

WSO2 ESB has defined some configuration parameters which controls the timeout of a particular request which is going out of ESB. In a particular  scneario, your client sends a request to ESB, and then ESB sends a request to another endpoint to serve the request. CLIENT->WSO2 ESB->BACKEND The reason for clients getting timeout is that ESB timeout is larger than client's timeout. This can be solved by either increasing the timeout at client side or by decreasing the timeout in ESB side. In any of the case, you can control the timeout in ESB using the below properties. 1) Global timeout defined in synapse.properties (ESB_HOME\repository\conf\) file. This will decide the maximum time that a callback is waiting in the ESB for a response for a particular request. If ESB does not get any response from Back End, it will drop the message and clears out the call back. This is a global level parameter which affects all the endpoints configured in ESB. synapse.global_timeout_inte...
6 comments
Read more