编程经典案例

Title: Building a Remote Method Invocation (RMI) Application in Java

Introduction to RMI:

Remote Method Invocation (RMI) is a mechanism in Java that allows an object residing in one system (usually a server) to invoke methods on an object residing in another system (usually a client). RMI enables distributed computing in Java, where objects can interact with each other across different JVMs (Java Virtual Machines) running on different hosts.

Objective:

In this tutorial, we'll create a simple RMI application in Java to demonstrate how RMI works. We'll build a server that provides a service to add two numbers remotely, and a client that invokes this service.

Step 1: Define the Remote Interface:

```java

import java.rmi.Remote;

import java.rmi.RemoteException;

public interface Calculator extends Remote {

int add(int a, int b) throws RemoteException;

}

```

Step 2: Implement the Remote Interface on the Server Side:

```java

import java.rmi.RemoteException;

import java.rmi.server.UnicastRemoteObject;

public class CalculatorImpl extends UnicastRemoteObject implements Calculator {

protected CalculatorImpl() throws RemoteException {

super();

}

@Override

public int add(int a, int b) throws RemoteException {

return a b;

}

}

```

Step 3: Create the Server:

```java

import java.rmi.registry.LocateRegistry;

import java.rmi.registry.Registry;

public class Server {

public static void main(String[] args) {

try {

Calculator calculator = new CalculatorImpl();

Registry registry = LocateRegistry.createRegistry(1099);

registry.rebind("CalculatorService", calculator);

System.out.println("Server started...");

} catch (Exception e) {

System.err.println("Server exception: " e.toString());

e.printStackTrace();

}

}

}

```

Step 4: Create the Client:

```java

import java.rmi.registry.LocateRegistry;

import java.rmi.registry.Registry;

public class Client {

public static void main(String[] args) {

try {

Registry registry = LocateRegistry.getRegistry("localhost", 1099);

Calculator calculator = (Calculator) registry.lookup("CalculatorService");

int result = calculator.add(5, 3);

System.out.println("Result: " result);

} catch (Exception e) {

System.err.println("Client exception: " e.toString());

e.printStackTrace();

}

}

}

```

Step 5: Compile and Run the Server and Client:

Compile all the Java files.

Start the server using `java Server`.

Run the client using `java Client`.

Conclusion:

In this tutorial, we've created a simple RMI application in Java. The server provides a remote service for adding two numbers, and the client invokes this service remotely. RMI simplifies distributed computing in Java by allowing objects to communicate across different JVMs seamlessly.

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