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Distributed Java: RMI Tutorial. 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. 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. 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. Based on: Java 8 Java program that uses ArrayList import java.util.ArrayList; public class Program The Java thread facility and API is deceptively simple; however, writing complex programs that use threading effectively is not. This tutorial explores threading. All language compilers translate source code into machine code for a specific computer. Java compilers also does the same thing. Java compiler produces an. You then pass this server object to the stock ticker service, which remembers it and calls its methods when the stock price changes. See RMI callback service for the big picture. Figure 2. RMI callback service. The code for the callback service comes in several parts. Because there are two servers, there are also two interfaces. The first is the interface for the Ticker. Server service. There is only one method, connect( ), which takes one argument, a Client: package rmi. Remote. import java. Remote. Exception. Ticker. Server extends Remote . It also has only one method, alert( ), which takes a String argument: Client. BEGIN main. package rmi. About the Author As the founder of Mountain Goat Software, Mike Cohn specializes in helping companies adopt and improve their use of agile processes and techniques to. Bob Lee (a.k.a CrazyBob) has started a series on hardcore Java. The first installment offers an example loaded view on how one can use a thread local variable to. Client - - the interface for the client callback */. Client extends Remote . Its constructor starts a. A real implementation might. RMI service to track actual stock data. The connect(. ) method is trivial; it just adds the given client (which is really. RMI proxy for the client server running on your desktop). The. run method runs forever; on each iteration, after sleeping for a. If there’s an error on a given client, the. Ticker. Server. Impl. Remote. Exception. Unicast. Remote. Object. Array. List. import java. Iterator. import java. List. import java. Random. /** This is the main class of the server */. Ticker. Server. Impl. Unicast. Remote. Object. Ticker. Server, Runnable. This won\'t get. * called until the client starts up. More interesting is the client application shown in. Callback Client. Program. RMI client to the connect(. RMI server to the alert( ) method in the server. Ticker. Server. Impl. Callback Client. Program. This class tries to be all things to all people. A more realistic version would. GUI control to decide whether the given price movement is considered. JOption. Pane (see.
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