Java RMI Presentation

Editor's Notes

• #2: Hello everybody, welcome to my presentation.This is Mohammad Masudur Rahman.Today, I am going to talk about a very interesting topic about distributed computing called Remote Method Invocation.Hope you will enjoy the topic.
• #3: RMI is copyrighted by Sun Micro systemCurrently SUN is taken by Oracle, so, now this technology belongs to Oracle corporation.
• #4: In my presentation, I am going to cover the following topics I am not going to read it out, but we will try to go step by step.
• #5: Before discussing about Java RMI,the very first thing I would like to focus.What is a distributed object technology (DOT)?Also, what is the difference between web application and web service?So, concept is pretty simple like this diagram. When a machine can access the functionality of an object situated in a remote machine and exploit the computation power of the remote machine, then we can call it as a distributed object technology (DOT)Java RMI is a perfect example of distributed object technology. Other similar types of technology is CORBA, SOAP etc.
• #6: As mentioned, Java RMI is a distributed object based technology that means it provides object level abstraction to the developer.For example, the developer needs to access some functionality of a remote object, Java RMI manages to allow the developers to call that remote object from his program just like a local class object. This was a cool thing when the concept was first started by Sun Microsystems and whole features were packaged as a Java Library with SDK.It is also considered as an object version of Java RPC which provides procedure level abstraction to the developer.Java RMI is basically a Java based technology and any machine containing JVM can host a distributed object server or client. However, it involves several components like service interface, RMI registry, skeleton, stubs etc which will discuss in the later slides.The are also some advanced features related to RMI like object serialization, parameter marshalling on which we will try to provide some overview.
• #7: Lets take a look into the technology hierarchy.The primary communication technology is Socket in Java : abstraction is low level, that means developer needs to think about more details about the technology rather than his application which is time-consuming.The next level is RPC, which provides method level abstraction, that means to call a remote method, you have to provide the method name and parameters though some RPC Client to get access to the functionality; that means, still you need to care about method name, type and # of parameters which may not be comfortable for all.The next level is object level technology which provides object level abstraction. Other parallel object technology is CORBA by OMG and SOAP by Microsoft.CORBA is C++ in server, but the service interface is implemented in IDL (Interface definition language) which is platform independent, so, any client can communicate with it. IDL creates different service interfaces for different clients.SOAP is mainly intended for web service architecture. Any client having access to WSDL file can actually access the service.
• #8: XDR = External data representation, a data format for network transmission, developed by Sun Microsystems, 1980 Encoding > XDR >Decoding of data.Base unit is 4 bytes.CORBA= Common Object Request Broker Architecture, client and server both communicate with the ORB (Object Request Broker) to get and provide service.IIOP = ORB protocol over the Internet which started on 1994 to provide a greater degree of interoperability.Java IDL = Provides Java interface definition to different other languages.RMI IIOP=Java RMI over IIOP, that means RMI uses IIOP to exploit the CORBA features like OMG IDL or non-java platform access.
• #9: Lets focus on RMI architecture. The discussion will be two-folds:Layered based architectureWorking principles based
• #10: Here, we can see a list of layers in the RMI protocol.In the application layer, there are client and server who are the end-consumer and end-producer of the service. They communicate with intermediate layer called stub-skeleton layer.In stub-skeleton layer, stub is related to client application which actually transmits the request to the next level. The skeleton is a component which is associated with server and is responsible to make the actual request to the server.Remote reference layer contains the RMI registry and it works like a ORB in CORBA, that means, it handles the request and response between client and server. Once the client gets the remote object reference from the RMI registry, it can make request and this layer transmits that request to the appropriate server. Again, when server responds, it also sends back the response to the client. It also manages other advanced tasks like object activation , object serialization management, distributed garbage collection etc.Transport layer handles network communication between client and server.
• #11: We have discussed these already.
• #12: Now comes the working principles.We can see the following steps:Client requests for the remote object reference to naming serviceOnce the naming service locates the server host, RMI registry provides a stub (proxy) of remote object.Client can make call using the stubBasically, the request from the stub is sent to the server skeleton which makes the actual request to the remote object.Similarly, the server response is sent back through skeleton and stub to the client.
• #13: Now, we will show how to develop a simple RMI application.
• #14: There are 3 major steps for this development.Service contract establishment and server application developmentClient application developmentDeployment of service
• #15: First comes the service contract.Suppose, the client and server are agreed upon this contract that there will be 3 operations:Factorial operationPrime check operationSquare operationI kept the examples simple for easy understanding.
• #16: And here is the complete interface. We developed it using Java interface. We named it MathService.
• #17: Here, the serverapplication implements the service interface.
• #18: This code binds the MathService to the RMI registry so that client app can get the reference of the serviceAnd consume the service.Interestingly, client can actually access the reference of interface MathService to make call, however, the respond is provided by the object implementing the service.
• #19: Now comes the client application development.
• #20: Here, we can see, client accesses the Naming. lookup() method to get the reference of the remote object.
• #21: Once it gets the reference, client can call the method just like it is calling a local object method.This is the strength of Java RMI technology.
• #22: Now comes the deployment.
• #23: We need to start the RMI registry service to deploy the remote object; server object.
• #24: Here we are compiling both service and server object.
• #25: Then we are creating skeleton of server object. This step is deprecated from JDK 1.5 as JDK automatically creates it.The developer does not need to do it manually now.
• #26: Now comes the crucial part on which often most of time we get stuck.That is the security policy of Java RMI.The default security does not support the RMI call, so, we need to set custom permission for the call to the security manager.This phase is required for both the client and server.Basically, we have to create a <any name>.policy file with this content. Here, we allowed all types of call associated with Java RMI;That is why it contains AllPermission.
• #27: This is how the server object should be deployed.
• #28: This is how we did.
• #29: This is how the client needs to be run for RMI service access. Please note that we have to specify the host name.
• #30: This is how we did for the client. However, we also developed the Java object serialization by this time.
• #31: There are advance stuffs which I would like to provide some overview.Java Object serialization: It involves converting the object into a sequence of byte streams where there needs a swapping of java object between client and the server. Basically, if client or server uses a user-defined class as parameters, then they need the object serialization.Parameter Marshalling is a type of serialization for parameters handled by the stub-skeleton layer. Demarshalling refers to de-serialization.Object Activation: In some scenarios, server may not be running always, then object reference layer activates the target remote object (server) to enable it to respond to the client’s request. Common for infrequent RMI call.The detail discussion of those topics is beyond this tutorial, because each of them will be a single tutorial.
• #32: These are strengths of Java RMI.-Object oriented, object level abstraction.-Mobile behavior: that means the roles between client and server can be exchanged easily.-It supports the design pattern-sate and secure like the Java technology.
• #33: -It can support the legacy system.-Write once, run everywhere-Distributed garbage collection, like the one provide by Java.-facilitates the parallel computing.-Widely supported by different versions of JDK, as it was from the beginning, JDK 1.1
• #34: It also got some weaknesses.-Tied to Java system, that means it a Java only technology, cant communicate well with the non-java platform.-Due to byte code step, the computation is slower.-Additional complexity for security which many developers didn’t like.-Extra step with rmic compilation
• #35: Now, we will do a comparative study between RMI and its parallel technologyCORBA
• #36: We will choose several perspective to compare between these two technologies:Language dependence: Java is tied to Java, that means client server and interface all are in java, but its not the case in CORBA. The core/server of CORBA in C++, but the IDL provides language specific service interface, so that any client can call the server. This makes CORBA platform language independent service.Mobile behavior: Java RMI can show it as the roles between client and server can be easily exchanged; not possible for CORBAPerformance Issue: For byte code step, Java RMI fall backs in heavy computation. On the other hand, C++ of CORBA is compiling language and performs faster
• #37: There are more:4. Ease of use: RMI is easy to use, but CORBA is complex and may not easy for all.5. Maturity: CORBA is a matured technology and already lots of applications are using this technology, whereas RMI is less matured compared to it.
• #38: Java RMI has got several big customers due to its remarking features.
• #39: CORBA is a well established technology and started earlier than RMI. It got huge audience. Please check the link for details.Few are shown here.
• #40: So>None is better than otherYou need to choose based on the scope and type of the technical requirements.For example, if you need low overhead, easy to use technique and platform independence is not a requirement, then you can choose RMIFor opposite reasons, you can choose CORBA, but beware of the expertise of the developers
• #41: So, we have got couple of conclusions to make.Discuss on your own.