Rmi how does it work

First, we need to tell RMI where to find any other classes it needs. We can use the system property java. When RMI sends a serialized object i.

If the recipient needs the class file in addition to the data, it fetches the file at the specified URL. In addition to stub classes, other classes referenced by remote objects in the application can be loaded dynamically.

In Figure We can now split our class files between the server and client machines. For example, we could withhold the MyCalculation class from the server, since it really belongs to the client. Note that the trailing slash in the URL is important: it says that the location is a base directory that contains the class files. Next we have to set up security.

Since we will be loading class files over the network and executing their methods, we must have a security manager in place to restrict the kinds of things those classes may do, at least in the case where they are not coming from a trusted code source. RMI will not load any classes dynamically unless a security manager is installed.

One easy way to meet this condition is to install the RMISecurityManager as the system security manager for your application. It is an example security manager that works with the default system policy and imposes some basic restrictions on what downloaded classes can do. Here is an example policy file—call it mysecurity. Finally, there is one last magic incantation required to enable dynamic class loading. As of the current implementation, the rmiregistry must be run without the classes which are to be loaded being in its class path.

If the classes are in the class path of rmiregistry , it will not annotate the serialized objects with the URLs of their class files and no classes will be dynamically loaded. This limitation is really annoying; all we can say is to heed the warning for now.

If you meet these conditions, you should be able to get the client to run starting with only the MyClient class and the RmtServer remote interface. All of the other classes will be loaded dynamically from a remote location.

The StringIterator is a simple list of strings, with some methods for accessing the strings in order. We will make it a remote object, so that implementations of StringIterator stay on the server. Along with the request, our client passes a reference to a WorkListener object that is to be notified when the WorkRequest is done.

Because this is to be a remote object, our interface must extend Remote , and its methods must throw RemoteException s:. This is the interface that defines how an object should listen for a completed WorkRequest. It has one method, workCompleted , which the server that is executing a WorkRequest calls when the job is done:. We need to add implementations of the getList and asyncExecute methods, which we just added to the RmtServer interface:.

Our implementation of asyncExecute is a little cheesy. The thread would call workCompleted at a later time, when the computation was done. In this simple example, it would probably take longer to start the thread than to perform the calculation. We have to modify MyClient to implement the remote WorkListener interface. We also add the workCompleted method that the WorkListener interface requires:. Finally, we want MyClient to exercise the new features. Add these lines after the calls to getDate and execute :.

We use getList to get the iterator from the server, then loop, printing the strings. We also call asyncExecute to perform another calculation; this time, we square the number The second argument to asyncExecute is the WorkListener to notify when the data is ready; we pass a reference to ourself this. Now all we have to do is compile everything and run rmic to make the stubs for all our remote objects:. You should get the following:. And, conversely, you should be able to have the MyServer download the Client stub and WorkRequest related classes when it needs them.

We hope that this introduction has given you a feel for the tremendous power that RMI offers through object serialization and dynamic class loading. Java is one of the first programming languages to offer this kind of powerful framework for distributed applications. One of the newest features of RMI is the ability to create remote objects that are persistent.

They can save their state and be reactivated when a request from a client arrives. This is an important feature for large systems with remote objects that must remain accessible across long periods of time. RMI activation effectively allows a remote object to be stored away—in a database, for example—and automatically be reincarnated when it is needed.

Much of the functionality of activatable objects can be achieved by using factories of shorter-lived objects that know how to retrieve some state from a database or other location. The primary users of RMI activation may be systems like Enterprise JavaBeans, which need a generalized mechanism to save remotely accessible objects and revive them at later times. So this solution is somewhat limited at this time.

Skip to main content. Start your free trial. To implement the remote interface, the class should extend to UnicastRemoteObject class of java.

Also, a default constructor needs to be created to throw the java. RemoteException from its parent constructor in class. Its prototype is rmic classname. For above program the following command need to be executed at the command prompt rmic SearchQuery.

Step 4: Start the rmiregistry Start the registry service by issuing the following command at the command prompt start rmiregistry Step 5: Create and execute the server application program The next step is to create the server application program and execute it on a separate command prompt.

The server program uses createRegistry method of LocateRegistry class to create rmiregistry within the server JVM with the port number passed as an argument. The rebind method of Naming class is used to bind the remote object to the new name. The lookup method of the Naming class is used to get the reference of the Stub object. In order to access the remote object from another machine, localhost is to be replaced with the IP address where the remote object is present.

Stub and Skeleton objects are used for communication between the client and server-side. This article is contributed by Aakash Ojha. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to review-team geeksforgeeks. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. Skip to content.

At the server side, the packed parameters are unbundled and then the required method is invoked. This process is known as unmarshalling. RMI registry is a namespace on which all server objects are placed. Each time the server creates an object, it registers this object with the RMIregistry using bind or reBind methods. These are registered using a unique name known as bind name. To invoke a remote object, the client needs a reference of that object.

At that time, the client fetches the object from the registry using its bind name using lookup method. Previous Page. Next Page.