Simple Rmi Program Using Netbeans Java

At its simplest level, remote procedure call is the ability to run code on another machine and have it behave as much as possible like a local method call. Most versions of Unix use remote procedure calls extensively: Sun/Oracle NFS, YP/NIS, and NIS+ are all built on top of their RPC mechanism.

RMI, CORBA and NetBeans. Initial definition of an Java remote interface (RMI based) using NetBeans. Build simple tools to solve complex problems.

Another RCP implementation for UNIX is called DCE; Microsoft Windows implements large parts of the Unix DCE Remote Procedure Call specification and can interoperate with it. Each of these defines its own slightly ad hoc method of specifying the interface to the remote call. Sun/Oracle RPC uses a program called rpcgen, which reads a protocol specification and writes both the client and server network code. These are both Unix-specific; they have their place but aren’t as portable as Java.

Use the JNDI static method Naming.lookup( ), passing in the lookup name. This gives you a reference to a proxy object, an object that, like the real server object, implements the remote interface but runs in the same Java Virtual Machine as your client application. Here we see the beauty of interfaces: the proxy object implements the interface so that your code can use it just as it would use a local object providing the given service.

And the remote object also implements the interface so that the proxy object’s remote counterpart can use it exactly as the proxy is used. Shows the client for the RemoteDate service. One major benefit of RMI is that almost any kind of object can be passed as a parameter or return value of a remote method.

The recipient of the object will not know ahead of time the class of the actual object it will receive. If the object is of a class that implements Remote (java.rmi.Remote), the returned object will in fact be a proxy object that implements at least the declared interface. If the object is not remote, it must be serializable, and a copy of it is transmitted across the Net. The prime example of this is a String. It makes no sense to write an RMI proxy object for String.

Remember from that String objects are immutable! Once you have a String, you can copy it locally but never change it. So Strings, like most other core classes, can be copied across the RMI connection just as easily as they are copied locally. But Remote objects cause an RMI proxy to be delivered. So what stops the caller from passing an RMI object that is also itself a proxy? Nothing at all, and this is the basis of the powerful RMI callback mechanism.

An RMI callback occurs when the client of one service passes an object that is the proxy for another service. The recipient can then call methods in the object it received and be calling back (hence the name) to where it came from.

Think about a stock ticker service. You write a server that runs on your desktop and notifies you when your stock moves up or down. This server is also a remote object. You then pass this server object to the stock ticker service, which remembers it and calls its methods when the stock price changes. See for the big picture. Now that you’ve seen both interfaces, let’s look at the TickerServer implementation ().

Its constructor starts a background thread to 'track' stock prices; in fact, this implementation just calls a random number generator. A real implementation might use a third RMI service to track actual stock data. The connect( ) method is trivial; it just adds the given client (which is really an RMI proxy for the client server running on your desktop). The run method runs forever; on each iteration, after sleeping for a while, it picks a random stock movement and reports it to any and all registered clients. If there’s an error on a given client, the client is removed from the list. Here’s a program I put together while teaching Java courses for Learning Tree ().

In one exercise, each student starts the RMI registry on his or her machine and uses Naming. Dp Gympac 2500 Dl Manual more. rebind( ) (as in ) to register with it. Some students come up with interesting variations on the theme of registering.

This program contacts the RMI registry on each of a batch of machines and shows the instructor graphically which machines have RMI running and what is registered. A red flag shows machines that don’t even have the registry program running; a black flag shows machines that are dead to the (networked) world. This program also uses many ideas from elsewhere in the book. A Swing GUI () is used. The layout is a GridLayout (discussed briefly in ). A default list of machines to watch is loaded from a Properties object ().

For each host, an RMIPanel is constructed. This class is both a JComponent () and a thread (). As a JComponent, it can be run in a panel; as a thread, it can run independently and then sleep for 30 seconds (by default; settable in the properties file) so that it isn’t continually hammering away at the RMI registry on all the machines (the network traffic could be awesome). This program combines all these elements and comes out looking like the display in (alas, we didn’t have color pages in earlier editions of this book, so somebody converted the illustrations to grayscale). The per-machine class, RMIPanel, is shown in. This class is instantiated once for each machine being monitored. Its run method loops, getting the list of registered objects from the given machine’s RMI registry, and checks the contents to see if the expected string is present, setting the state to one of several integer values defined in the parent class NetPanel (EMPTY, DUBIOUS, FINE, etc.) based on what it finds.

Illustrator Cs6 Download Free Portable Game. This state value is used to decide what color to paint this particular RMIPanel in the setState( ) method of the parent class NetPanel, which we have no reason to override.