I'm having trouble undrstanding the difference about both platforms?
Both seem to offer an environment for deploying and managing applications.
First I thought app servers use OSGi under the hood, I don't think so now but I see large AS (jboss, glassfish, websphere, etc) use OSGi.
What's the big picture?
Thank you
There is (to some extend) an overload of the term "application".
OSGi is a runtime environment (and development model) for modular Java applications. The term "application" in this case can be really, really low level. For example, an application server can be considered such an "application".
Application servers are also a runtime environment (and development model) for Java applications. However, the term "application" in this case typically refers to a higher level application type (eg., web applications). Application servers typically include a rich set of higher functionality and programming APIs for building web applications (Servlets), persisting data into databases (JPA) and clustering capabilities. Most application servers these days are composed of modules (eg., core, servlet engine, EJB container, etc.). Some application servers use OSGi under the covers. Others have their own modular runtime environment which also offers OSGi capabilities.
But it's also possible to develop higher level applications (such as web applications) directly using only OSGi runtime environment. However, an OSGi framework itself does not include any of the additional functionality. It has to be assembled yourself. There are some "distributions" that include a framework and several modules.
Related
Lately I started to learn Java EE and related technologies and there are some concepts which confuse me. Somewhere I read that whenever one is building a Java EE application then it is sort of mandatory to use a container.
Currently, I am learning Spring framework and trying to build a small application with it to get hands-on. Now in that I am not sure if it is mandatory for me to use a container (say Tomcat) or it depends application which I am building that I need a container or not.
If it depends on the application that one is building, then what are the factors which help to decide whether a container should be used or not?
Puuhhh, this is a very big question and there is no simple answer. But I will do my best to explain my own opinion at least:
What are containers?
Containers provide functionality to you. Such a functionality can be to handle web request and dispatch them to servlets - in this case we call them servlet containers (e.g. Tomcat or Jetty).
But containers can also provide other things, e.g. they can provide user authentication, logging or the connection to a database. Most containers (e.g. Tomcat) do multiple of those things (e.g. Tomcat does all I mentioned). Some containers do more then others, e.g. JBoss can do much more than Tomcat.
Trade Off
However, there is a trade off: If you use a simple container (like Tomcat), you need to do a lot of things on you own or by using other Frameworks (like Spring). But if you use a powerful container, you must know the container very well and the chance is high that your application will depend on this concrete container sooner or later.
The point, that using a container is not mandatory. It is a decision. Some people will argue for it, others against it. But depending on the books you read, this decision is already made (e.g. J2EE needs a J2EE container, that's how it works).
The trend (IMHO)
Years ago the trend was to use big and powerful (J2EE) containers which provide as much as possible. IMHO the trend today is to use smaller and light-way solutions. Most developers would prefer to use a Tomcat server instead of a JBoss server today.
Frameworks without containers
While J2EE needs a container, there are other frameworks/technologies which supports the development of web applications without any external container. Such frameworks are Play! or Spark Java.
Note
If you are not familiar with containers and Spring, take care to don't get confused. Most applications you will develop with Spring are web applications which will be deployed to a servlet container. This is very common. But Spring doesn't relay on that. You can also use Spring without such a container, e.g. to develop a desktop application. But if you want to develop a web application, the Java-way is to use a servlet container.
If your application is using servlets, you'll need a container to handle the requests. Tomcat is a very popular choice.
I'll anticipate your next topic to cover with this discussion of "application server" versus "container."
There are two containers. One is Web Container (IIS, Apache) to run Web Applications and another is "Application Container" to run Enterprise Applications.
Web Applications = Apps developed using HTML, XML, CSS and JSPs
Enterprise Applications = Apps developed used JAVA, J2E and Serverlets in addition to HTML and XML.
I am considering writing a new set of applications using OSGi, but they will need to interact heavily with existing non-OSGi applications.
To clarify, the new applications will need to call into existing non-OSGi code bases maintained by other teams (usually propriety services of varying protocols), and new non-OSGi applications will need to call the new OSGi services.
I am not seeing much documentation for how to do this.
Can someone please point me to the correct steps
It sounds like you want to embed OSGi into a larger application. A good starting point for this is a blog post I wrote some time ago: http://njbartlett.name/2011/07/03/embedding-osgi.html
The trick to creating visibility between OSGi bundles and the objects "outside" OSGi is to publish and/or consume services using the system bundle's BundleContext. The embedding code must be aware of the objects from the outer application that you want to make visible into OSGi, and it should publish them as services. Be aware that you need to export the service interface packages via the system bundle exports -- how to do this is described in the blog post.
OSGi services are only for communications inside the same JVM process. So I guess you want to communicate between processes. In this case you have all the usual remoting protocols like SOAP, Rest, RMI. On the OSGi side you can bridge from OSGi services to offering SOAP or REST endpoints using Distributed OSGi (DOSGi).
We are developing a open source trading platform based on Springframework and Hibernate http://code.google.com/p/algo-trader/ and http://www.algotrader.ch. The application consists of a trading framework and several strategies that can be started independently. So far, these different parts have been running in separate JVM's communicating through RMI and JMS.
To avoid unnecessary serialization and network overhead we would like to run the entire application within some sort of container (potentially an application server). We do however have the requirement, that the individual parts of the application can be deployed, started and stopped independently.
We have looked into OSGi, but a lot of the libraries that we use are not OSGi ready yet, so this is not currently an option. Also please note, there is no web-GUI in our application.
Any suggestions on this?
Thanks
Andy
If OSGI is not an option then functionality can be broken into smaller units and then deploy them as utility jar, if deployed as utility jar they can be managed independently.
For application server I feel either glassfish or Jboss will be a good option considering they are open source and free.
Though at a later point in time you can check with Weblogic (Dev free).
So in your case you would like to break the static data configuration(Counterparty, Currencies), Dealing(Pricing, Quoting, Booking) as two separate feature.
For your choose of an application server i advise you Jboss and specially in his version 7.1 which is faster and more stable!
We're working on an OSGi-based infrastructure for processing stream-based data flows. Specific processing tasks are executed by individual OSGi components. We now need the possibility to distribute those components over different machines, which means, we need some kind of communication mechanism between OSGi components/containers.
During my research I came across different potential solutions: R-OSGi, Apache CXF for Distributed OSGi, Eclipse Communication Framework.
ECF seems particularly interesting as it supports different transports formats and provides support for stuff like service discovery.
My central questions:
Are there any detailed tutorials/walk-throughs for setting up an ECF infrastructure within Felix? (from my research, I found, that Felix support has been added recently)
Are there any solutions besides the three listed above which I might have missed?
Is there a reason for taking Apache CXF instead of ECF?
The first question -- whether there is a detailed walk-through for setting up ECF with Felix -- I don't know the answer to, though one might use a search engine to find out combinations of those terms.
The problem is ECF uses the Equinox infrastructure, and has at times inadvertently relied on packages that are non-public through transitive dependencies (particularly the Runtime API which uses Equinox for non-public debugging). This, in turn, means that ECF relies on a whole host of other components to be available and it's this set which typically isn't well defined on a Felix runtime.
You have missed out Paremus' Service Fabric, which is a commercial OSGi cloud solution. I'm not sure if you were specifically focussing on open-source or not; but if you are including commercial licenses then they have a very robust architecture for remote services.
Finally, the Apache CXF over ECF question -- if you're using Felix, I'd argue that going with Apache CXF is probably easier than going with ECF. This is mainly due to the dependency set and getting it working, combined with the fact that ECF may not be tested on Felix and so may assume particular aspects of the Equinox runtime (which includes, for example, the runtime's parent classloader delegation to pick up things on the boot classpath). This isn't really the fault of ECF per se, but rather an artefact of how the Eclipse ecosystem works.
If you want to communicate with non-OSGi runtimes, there's an advantage in the Apache CXF in that they can generate WDSL for interaction with other languages. I believe that you can do the same thing in ECF with a bit more work. The CXF solution is likely to be more verbose than a corresponding ECF one (WSDL always is) but if you're not using high volumes of requests this isn't likely to make a significant difference.
I have been trying to understand a bit more about the wider picture of OSGi without reading thru the entire specification. As with so many things, the introduction to what OSGi actually is was probably written by someone who had been working on it for a decade and perhaps wasn't best placed to put themselves in the mindset of someone who knows nothing about it :-)
Looking at Felix's example DictionaryService, I don't really understand what is going on. Is OSGi a distinct instance of a JVM into which you load bundles which can then find each other?
Obviously it is not just this because other answers on StackOverflow are explicit that OSGi can solve the dependency problem of a distributed system containing modules deployed within distinct JVMs (plus the FAQ keeps talking about networks).
In this latter case, how does a component running in one JVM interact with another component in a separate JVM? Can the two components "use" each other as if they were running within the same JVM (i.e. via local method calls), and how does OSGi manage the marshalling of data across a network (do you have to use Serializable for example)?
Or does the component author have to use some other distinct mechanism (either provided by OSGi or written themselves) for communication between remote components?
Any help much appreciated!
Yes, OSGi only deals with bundles and services running on the same VM. However, one should note that it is a distinct feature of OSGi that it facilitates running multiple applications (in a controlled way and sharing common modules) on the same JVM at all.
When it comes to accessing services outside the clients JVM, there is currently no standardized solution. Paremus Infiniflow and the derived open-source project Newton use an SCA approach. The upcoming 4.2 release of the OSGi specs will address one side of the problem, namely how to use generic distribution software in such a way that it can bring remote services into the client's JVM.
As somebody mentioned R-OSGi, this approach also deals with the other side of the problem, being how to manage dependencies between distributed OSGi frameworks. Since R-OSGi is not generic distribution software but explicitly deals with the lifecycle issues and dependency management of OSGi bundles.
As far as I know, OSGi does not solve this problem out of the box. There are OSGi-bundles, for example Remote OSGi, which allow the programmer to distribute services across a network.
Not yet, i think it's being worked on for the next release.
But some companies have already implemented distributed osgi. One i'm aware of is Paremus' Infiniflow (http://www.paremus.com/products/products.html). At linkedin they are also working on this. More info here: Building Linkedin next gen architecture with osgi and here: Matt raible: building linkedin next gen architecture
Here's a summary of the changes for OSGI 4.2: Some thoughts on the OSGi R4.2 draft, There's a section on RFC-119 dealing with distributed OSGi.
AFAIK, bundles are running in the same JVM, but are not loaded using the same class loader (that why you can use two different versions of the same bundle at the same time).
To interact with components in another JVM, you must use a network protocol such as rmi.
The OSGi alliance is working on a standard for distributed OSGi:
http://www.osgi.org/download/osgi-4.2-early-draft2.pdf
There even is an early Apache implementation of this new standard:
http://cxf.apache.org/distributed-osgi.html
#Patriarch24
The accepted answer to this question would seem to indicate otherwise (unless I'm misreading it). Also, taken from the FAQ:
The OSGi Service Platform provides the functions to change the composition dynamically on the device of a variety of networks, without requiring a restart
(Emphasis my own). Although in the same FAQ it describes OSGi as in-VM.
Why am I so confused about this? Why is such a basic question about a decade-old technology not clear?
The original problem of OSGI was more related to distribution of code (and then configuration of bundle) than to distribution of execution.
People looking at distributed components are rather looking towards SCA
The "introduction" link is not really an intro, it is a FAQ entry. For more information, see http://www.osgi.org/About/WhatIsOSGi Not hard to find I would think.
Anyway, OSGi is an in-VM SOA. That is, the OSGi Framework is about what happens inside the VM, it provides a framework for structuring your application inside the VM so you can built it too a large extent from components. So the core has nothing to do with distribution, it is completely oblivious of who implements the services, it just provides a mechanism for modules to meet each other in a loosely coupled way.
That said, the µService model reifies the joints between the modules and it turns out that you can build support on top of the framework that provides distribution to the other components. In the last releases we specified some mechanisms that make this standardized in the core and provide a special service Remote Service Admin that can manage a distributed topology.
If you are looking for a distributed OSGi centric Cloud runtime - then the Paremus Service Fabric ( https://docs.paremus.com/display/SF16/Introduction ) provides these capabilities.
One or more Systems each consisting of a number of OSGi assemblies (Blueprint or Declarative Services) can be dynamically deployed and maintained across a population of OSGi runtime Frameworks (Knopflerfish, Felix or Equinox).
A light weight RSA remote framework is provided which provides Service discovery by default using DDS (a seriously good middleware messaging technology) - (thought ZooKeeper and other approach can be used). Currently supported re-moting protocols include RMI and Avro.
Regards
Richard