Java远程方法调用(RMI)

Java远程方法调用(Java Remote Method Invocation，简称RMI)是实现RPC的一种机制。Java RMI实现过程可分为以下几个步骤：

1.       创建远程接口及声明远程方法；

2.        创建远程对象及实现远程方法；

3.        服务器端启动RMI注册服务，注册远程对象；

4.        客户端查找远程对象并调用远程方法。

远程接口具有如下特点： 

1. 远程接口必须为public属性。如果不这样，除非客户端与远程接口在同一个包内，否则 当试图装入实现该远程接口的远程对象时，调用会得到错误结果。 

2. 远程接口必须扩展接口java.rmi.Remote。 

 

  3. 除与应用程序本身特定的例外之外，远程接口中的每个方法都必须在自己的throws从句中 声明java.rmi.RemoteException。（或 RemoteException 的父类）。 

4. 作为参数或返回值传递的一个远程对象(不管是直接，还是本地对象中嵌入)必须声明为远 程接口，而不应声明为实施类。

  5. 参数或返回值若为对象，该对象必须实行序列号接口 Serializable

 

其代码如下：

1)      创建远程接口及声明远程方法

 

package com.server;

import java.rmi.Remote;
import java.rmi.RemoteException;

public interface RmiSample extends Remote{
	public int sum(int a, int b) throws RemoteException;
	
	public void save(Student s) throws RemoteException;
	
	public Student get() throws RemoteException;
}

 

2)      创建远程对象及实现远程接口方法

 

package com.server;

import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;

public class RmiSampleImpl extends UnicastRemoteObject implements RmiSample{

	/**
	 * 
	 */
	private static final long serialVersionUID = -7851182277085789517L;

	protected RmiSampleImpl() throws RemoteException {
		super();
	}
	
	@Override
	public int sum(int a, int b) throws RemoteException {
		return a + b;
	}

	@Override
	public void save(Student s) throws RemoteException {
		System.out.println("student id is :"+s.getId());
		System.out.println("student name is :"+s.getName());
	}

	@Override
	public Student get() throws RemoteException {
		Student s = new Student();
		s.setId(2);
		s.setName("学生2");
		return s;
	}

}

3)      服务器端启动RMI注册服务，将远程对象进行注册

package com.server;

import java.net.MalformedURLException;
import java.rmi.Naming;
import java.rmi.RemoteException;
import java.rmi.registry.LocateRegistry;

public class RmiSampleServer {
	 public static void main(String[] args) {   
	        try{   
	            LocateRegistry.createRegistry(8808);   
	            //LocateRegistry.createRegistry(1099);   
	            RmiSampleImpl server= new RmiSampleImpl();   
	            Naming.rebind("//localhost:8808/SAMPLE-SERVER" , server);
	            //Naming.rebind("server" , server);
	        }catch (MalformedURLException me){   
	            System.out.println("Malformed URL: " + me.toString());   
	        }catch(RemoteException re){   
	            System.out.println("Remote Exception: "+re.toString());   
	        }   
	    } 
}

4)      客户端查找远程对象并调用远程方法

package com.client;

import java.rmi.RemoteException;
import java.rmi.Naming;   

import com.server.RmiSample;
import com.server.Student;
  

public class RmiSampleClient {
	 public static void main(String[] args) {   
	        try {   
	            String url = "//localhost:8808/SAMPLE-SERVER";   
	            //RmiSample RmiObject = (RmiSample) Naming.lookup("server");
	        	RmiSample RmiObject = (RmiSample) Naming.lookup(url);
	            System.out.println(" 3 + 2 = " + RmiObject.sum(3, 2));
	            
	            Student s = new Student();
	            s.setId(1);
	            s.setName("学生1");
	            RmiObject.save(s);
	            
	            Student student = RmiObject.get();
	            System.out.println("student id is :"+student.getId());
	    		System.out.println("student name is :"+student.getName());
	        } catch (RemoteException rex) {   
	            System.out.println("Error in lookup: " + rex.toString());   
	        } catch (java.net.MalformedURLException me) {   
	            System.out.println("Malformed URL: " + me.toString());   
	        } catch (java.rmi.NotBoundException ne) {   
	            System.out.println("NotBound: " + ne.toString());   
	        }
	  
	    }   
}