Remote Method Invocation (RMI) tutorials and examples.
Stub & skeleton layer is present below the Java developer view. In this layer RMI utilizes the proxy designed patterns, as per description in a famous book known as Design patterns. For proxy patterns one object present in a context is presented by some other proxy present in other separate context. This given class shows the proxy patterns. Stub and Skeleton Layer
For using proxy pattern of RMI, Sub class has a vital role of
Let us now look at the implementation of higher leveled RMI architecture.
Three abstraction layers are involved in building the RMI implementation. First one is Stub & Skeleton layer that is present below the view of developer. Interception of this layer is done with method calls that are built by client, to referene variable which would be redirecting calls towards the remote services of RMI.
Next layer is known as remote reference layer. This understands that
One principle is associated with RMI architecture and that is the implementation of behavior and definition of behavior are totally separate concepts. Code is allowed by RMI which defines what behavior is and also the code which keeps it separate.
This is nicely fitted with the distributed system needs where clients have major concern regarding the service definition and servers to be focused to provide the services.
Remote service definition in RMI is coded by usage
Argument to the return values could be of any type including remote objects, primitive data type, and local objects. It could be said more precisely that any type’s entity could be passed from or to remote method, as long as this entity would be considered as a type’s instance which is primitive type, aserializable object, or a remote object, that shows that interface java.io.Serializable would be implemented.
There are few object types that are not upto any criteria and hence are
First thing shall be the determination of application architecture which includes the components that are accessible remotely or are the local objects. Steps included are: Remote interfaces are defined. Methods are specified by the remote interface which is remotely invoked by some client. Client would program towards the remote interface instead of implementation classes. Such interfaces design includes the object type determination which is used being parameters and which would
Distributed applications are madeup of classes and interfaces, just the way all other Java applications are made. Methods are declared by the interfaces. Methods which have been declared are implemented by the classes. Perhaps, an additional method would also be declared. In distributed applications certain implementations are present in Java virtual machines, however others are not. Objects along with method which could possibly be invoked are known to be the remote objects.
When a remote
Two separate programs are present in RMI applications, a client and a servlet. Typical program of servlet makes certain remote objects, makes the accessibility of the reference possible to these objects, or waits for invoking methods by the clients at these objects. Typical client progam gets reference to more than one remote object that is present at server which would invoke methods. Mechanism is provided by the RMI which makes communication between client and server. Also, information is passed
EJB makes use of the RMI framework to do the object distribution. EJB application server provides extra services for example object pooling, transaction, database connection pooling etc which is not provided by RMI. Programming efforts are simplified by these services that have been given by EJB server, at performance cost in comparison with plain RMI. Therefore, if performance is more important then go for pure MRI as a better solution.
Direct sockets are opened into server by RMI transport layer. Firewalls are present in many intranets which doesn’t permit this. To make through some firewall, within firewall trusted HTTP protocol embed the RMI call. RMI uses HTTP tunneling and this is done by the encapsulation of RMI calls present in HTTP POST request. HTTP Tunneling
• When HTTP requests may be forwarded by firewall proxy server just to some known HTTP port:
• By value, primitive types get passed. For example, Boolean, char, int etc.
• Being remote references, remote object references get passed which permits the client process to make the methods invoked.
• By object serialization, non remote objects get passed by value. Implementation of the java.io.Serializable interface shall take place which shall allow objects to get serialized.
Remote method’s invocation gets initiated by the client process, using calling method present
Certain basic object services are provided by the RMI that might get utilized on distributed application. Such services include:
• Object naming/registry service: Services might be provided by the RMI servers to clients by the registration of 1 or more than one remote objects, along with local RMI registry.
• Object activation service: Based on needs, server objects are provided. With absence of the remote activation service, there exists a need to register the server objects
Remote object is considered to be the one in which other JVM are used to invoke the methods. Remote interface gets implemented by the remote object class. RMI is that application that produces various remote objects.
Responsibility of a RMI Server is:
• To create the remote object’s instance e.g CarImpl instance = new CarImpl()).
• Export the remote object.
• Bind the remote object instance to the RMI registry.
Client’s incoming calls are being accepted
RMI or Java Remote Method Invocation gives means to Java program (present at a machine) to do communication with other objects present in other JVMs, address spaces or processes. RMI architecture’s important parts are the skeleton class, stub class and object serialization. Layered architecture is used by the RMI where layers are enhanced without having any affect at the other layers. To summarize the layers, proceed as following: Application Layer: Server program and the client.Stub