Java back-end development: Using Java Remote Method Invocation for API remote calling

Java is a high-level object-oriented programming language with good platform compatibility, security and stability. With the development of Internet technology, more and more applications require remote calls through APIs to achieve data sharing and information interaction. Java Remote Method Invocation (RMI) is a remote invocation technology based on the Java platform, which can realize remote method invocation between Java objects.

This article will introduce the concept, working principle and usage of Java RMI to help Java back-end developers make better API remote calls.

1. Java RMI Concept

Java RMI is a remote invocation technology based on the Java platform, which can realize remote method invocation between Java objects. Simply put, Java RMI allows client applications to indirectly call object methods on remote servers through the network in distributed systems and obtain the return results.

In Java RMI, client and server communication use Java objects as parameters and return values. These Java objects must be able to implement the Serializable interface so that they can be transmitted over the network. The RMI framework will automatically serialize parameters, return values ​​and remote objects, and then transmit them to the remote server through the network.

2. Working Principle of Java RMI

The working principle of Java RMI can be simply summarized in the following steps:

1. Create a remote object

First, you need to create a Java object that implements the Remote interface as a remote object. The remote object is created on the server side. The client can obtain permission to access the remote object through the remote reference (Remote Reference) and call methods on the remote object.

2. Register the remote object

Register the remote object into the RMI registry. The RMI registry is a binding mapping table that contains the name of a remote object and a remote reference. The client can obtain the remote reference by specifying the name. The RMI registry can run on the local JVM or on a remote JVM.

3. The client obtains a remote reference

The client needs to request a remote reference from the RMI registry to obtain permission to access the remote object. The client can use the lookup() method provided by the Naming class to implement this step. The lookup() method accepts a string parameter that specifies the name of the remote object to be found, and returns a remote reference.

4. The client calls the remote method

The client calls the method on the remote object through the obtained remote reference. The parameters and return value of the method will be transmitted to the remote server through the network for processing. and return the results to the client.

3. How to use Java RMI

The following describes how to use Java RMI to make API remote calls:

1. Write the remote interface

First, you need Write a remote interface and inherit the java.rmi.Remote interface. The interface defines the remote methods that need to be implemented, and the methods must declare that they throw java.rmi.RemoteException. For example:

import java.rmi.Remote;
import java.rmi.RemoteException;
public interface MyRemoteInterface extends Remote {
  public String sayHello() throws RemoteException;
}

2. Write a remote implementation class

Then, you need to write a remote object that implements the remote interface. The remote object needs to inherit the java.rmi.server.UnicastRemoteObject class and implement the methods defined in the interface. For example:

import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
public class MyRemoteObject extends UnicastRemoteObject implements MyRemoteInterface {
  public MyRemoteObject() throws RemoteException {}
  public String sayHello() throws RemoteException {
    return "Hello world!";
  }
}

3. Register the remote object

Register the remote object into the RMI registry so that the client can obtain the remote reference. For example:

import java.rmi.Naming;
import java.rmi.registry.LocateRegistry;
public class Server {
  public static void main(String[] args) throws Exception {
    LocateRegistry.createRegistry(1099); //启动RMI注册表
    Naming.rebind("MyRemoteObject", new MyRemoteObject()); //注册远程对象
    System.out.println("Server is running...");
  }
}

4. The client calls a remote method

The client needs to obtain a remote reference, and then call the method on the remote object through the remote reference. For example:

import java.rmi.Naming;
public class Client {
  public static void main(String[] args) throws Exception {
    MyRemoteInterface remote = (MyRemoteInterface) Naming.lookup("rmi://localhost/MyRemoteObject"); //获取远程引用
    String result = remote.sayHello(); //调用远程方法
    System.out.println(result);
  }
}

This article briefly introduces the concept, working principle and usage of Java RMI. Java RMI can be used to conveniently make remote method calls between Java objects and achieve the purpose of remote API calls. It is a very practical distributed technology. Therefore, understanding Java RMI is very important for Java back-end developers.

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