RMI The concept of

RMI(Remote Method Invocation) Remote method call is a kind of communication mechanism between computers by using remote object to call each other . Use this mechanism , Objects on one computer can call objects on another computer to get remote data .RMI yes Enterprise JavaBeans The pillar of , It's about building a distributed system Java A convenient way for applications . in the past ,TCP/IP Socket communication is the main means of remote communication , But this development method does not use the object-oriented method to achieve development , When developing such a communication mechanism, programmers often feel bored , Regarding this RPC(Remote Procedure Call） emerge as the times require , It makes it easier for programmers to call remote programs , But in the face of complex communications ,RPC Still not very good support , and RPC Failed to achieve object-oriented call development mode . in the light of RPC Service legacy ,RMI In front of the world , It's designed as an object-oriented way of communication , Allows programmers to communicate using remote objects , And support multi-threaded Services , This is a revolution in telematics , A new milestone for telecommunication .

Java RMI A method of is called remotely (Remote Method Invocation). It's a mechanism , Be able to make in some Java The object on the virtual machine calls another Java Methods on objects in virtual machine . Any object that can be called with this method must implement the remote interface .

RMI Development steps

  1. First, create a remote interface and declare a remote method , Note that this is the interface for communication between the two sides , Need to inherit Remote
  2. Develop a class to implement remote interface and remote method , It's worth noting that implementing classes requires inheritance UnicastRemoteObject
  3. adopt javac Command compile file , adopt java -server Command registration service , Start the remote object
  4. Finally, the client looks up the remote object , And call the remote method

Example source code ：

First of all, build a Model layer , Note that this object needs to be remotely transmitted , So you have to inherit Serializable

package com.blankjor.rmi;
import java.io.Serializable;
/**

* @desc Transport persistence layer calls data objects , Must be realized Serializable Interface 

* @author Blankjor

* @date 2017 year 5 month 30 Japan Afternoon 3:28:45

*/

public class EntityData implements Serializable {

private static final long serialVersionUID = 1L;

private int id;

private String name;

private String tel;
public int getId() {

return id;

}
public void setId(int id) {

this.id = id;

}
public String getName() {

return name;

}
public void setName(String name) {

this.name = name;

}
public String getTel() {

return tel;

}
public void setTel(String tel) {

this.tel = tel;

}
}

Create a remote interface MyRemote, Note that the remote interface must inherit Remote

package com.blankjor.rmi;
import java.rmi.Remote;

import java.rmi.RemoteException;
/**

* @desc Remote interface , Realization Remote

* @author Blankjor

* @date 2017 year 5 month 30 Japan Afternoon 2:49:05

*/

public interface MyRemote extends Remote {

EntityData sayHello() throws RemoteException;
}

establish MyRemoteImpl Implement remote interface MyRemote, Note that this is the remote object implementation class , Need to inherit UnicastRemoteObject,UnicastRemoteObject The required remote interface is realized 

package com.blankjor.rmi;
import java.rmi.RemoteException;

import java.rmi.server.UnicastRemoteObject;
/**

* @desc Interface implementation , In order to accomplish some remote functions , With the help of UnicastRemoteObject, automatically 

* @author Blankjor

* @date 2017 year 5 month 30 Japan Afternoon 2:50:39

*/

public class MyRemoteImpl extends UnicastRemoteObject implements MyRemote {
/**

* Must be realized , In order to throw out RemoteException

*

* @throws RemoteException

*/

protected MyRemoteImpl() throws RemoteException {

}
@Override

public EntityData sayHello() throws RemoteException {

EntityData ed = new EntityData();

ed.setId(1);

ed.setName("lyc");

ed.setTel("110");

return ed;

}
}

Set up a remote server , And register after opening 

package com.blankjor.rmi;
import java.rmi.Naming;

import java.rmi.RemoteException;

import java.rmi.registry.LocateRegistry;
/**

* @desc Register the remote service server 

* @author Blankjor

* @date 2017 year 5 month 30 Japan Afternoon 2:54:26

*/

public class MyRemoteServer {

public static void main(String[] args) {

try {

System.out.println(" The remote service is starting , Wait for the call ...");

// Instantiate the remote service object 

MyRemote remote = new MyRemoteImpl();

// Register binding 

LocateRegistry.createRegistry(1234);

Naming.rebind("rmi://localhost:1234/RemoteHello", remote);

} catch (Exception e) {

e.printStackTrace();

}

}

}

Results after operation ：

Client access to remote services , call 

package com.blankjor.rmi;
import java.net.MalformedURLException;

import java.rmi.Naming;

import java.rmi.NotBoundException;

import java.rmi.RemoteException;
/**

* @desc The client that invokes the remote service 

* @author Blankjor

* @date 2017 year 5 month 30 Japan Afternoon 3:00:02

*/

public class MyRemoteClient {

public static void main(String[] args) {

try {

// Looking for remote services 

MyRemote service = (MyRemote) Naming.lookup("rmi://localhost:1234/RemoteHello");

// Call the remote service method 

EntityData ed = service.sayHello();

System.out.println("Welcome " + ed.getName());

} catch (MalformedURLException | RemoteException | NotBoundException e) {

e.printStackTrace();

}

}

}

Results after operation ：

summary ：
  From the above process ,RMI To the server IP Address and port dependency is very close , But at the time of development, I didn't know the future server IP And how about the port , But the client program depends on this IP And port .
This is also RMI One of the limitations of . There are two ways to solve this problem ： One is to pass. DNS To solve , The second is to encapsulate IP Exposed to program code .
  RMI The second limitation of is RMI yes Java Remote call of language , The programming language at both ends must be Java Realization , For communication between different languages, consider using Web Service Or the common object request broker system （CORBA） To achieve .

Reference resources ：http://www.cnblogs.com/leslies2/archive/2011/05/20/2051844.html

 http://lavasoft.blog.51cto.com/62575/91679/

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