用 Java 实现 RMI 系统 - 表中没有这样的对象

Question

I am trying to implement a simple RMI system in Java using three pairs of client/servers. The createDrecord is just a test method for now.

Client Code:

public class ManagerClient { 

public static void main(String[] args) {
    try{
    System.setSecurityManager(new RMISecurityManager());
    ClinicServerInterface mtlServer = (ClinicServerInterface)Naming.lookup("rmi://localhost:2020/mtl");
    ClinicServerInterface lvlServer = (ClinicServerInterface)Naming.lookup("rmi://localhost:2021/lvl");
    ClinicServerInterface ddoServer = (ClinicServerInterface)Naming.lookup("rmi://localhost:2022/ddo");

    mtlServer.createDRecord("asdf", "asfa", "asda", "as", "asd");

    }catch(Exception e){
        e.printStackTrace();
    }
  }
}

Server Code:

public class ClinicServer implements ClinicServerInterface { 

private int port;
private String location;

public ClinicServer(int port, String location){
    this.port = port;
    this.location = location;
}

public static void main(String[] args){

    int mtlPort = 2020;
    int lvlPort = 2021;
    int ddoPort = 2022;

    try{
        ClinicServer mtlServer = new ClinicServer(mtlPort, "mtl");
        ClinicServer lvlServer = new ClinicServer(lvlPort, "lvl");
        ClinicServer ddoServer = new ClinicServer(ddoPort, "ddo");

        Remote mtlObj = UnicastRemoteObject.exportObject(mtlServer,mtlPort);
        Remote lvlObj = UnicastRemoteObject.exportObject(lvlServer,lvlPort);
        Remote ddoObj = UnicastRemoteObject.exportObject(ddoServer,ddoPort);

        Registry r = LocateRegistry.createRegistry(2020);

        r.bind("mtl", mtlObj);
        r.bind("lvl", lvlObj);
        r.bind("ddo", ddoObj);


        System.out.println("New Server is up and running!");

    }catch(Exception e){

        e.printStackTrace();
    }

}

@Override
public void createDRecord(String firstName, String lastName, String address, String phone, String specialization)
        throws RemoteException {
    System.out.println("Create D Record");

}

The server runs fine, with the message being displayed, but when I run the client, I get this as an error:

java.rmi.NoSuchObjectException: no such object in table
    at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(Unknown Source)
    at sun.rmi.transport.StreamRemoteCall.executeCall(Unknown Source)
    at sun.rmi.server.UnicastRef.invoke(Unknown Source)
    at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source)
    at java.rmi.Naming.lookup(Unknown Source)
    at assignment1.ManagerClient.main(ManagerClient.java:36)

where line 36 is this line in the ManagerClient class:

ClinicServerInterface lvlServer = (ClinicServerInterface)Naming.lookup("rmi://localhost:2021/lvl");

I've read other threads on here with a similar problem but can't seem to figure out how it applies to my code specifically.

Answer 1

int mtlPort = 2020;
int lvlPort = 2021;
int ddoPort = 2022;

You don't need different port numbers for different remote objects. You can use 2020 for all of them and the Registry too.

Registry r = LocateRegistry.createRegistry(2020);

You need to make this variable static. Otherwise it can be garbage-collected, which can lead to garbage-collection of the servers too, which is what causes this problem.

 System.setSecurityManager(new RMISecurityManager());

You don't need a security manager in the client unless you're using the RMI codebase feature, which isn't mentioned in your question.

ClinicServerInterface lvlServer = (ClinicServerInterface)Naming.lookup("rmi://localhost:2021/lvl");

This will get a java.rmi.ConnectException , as the port number isn't 2020.

Answer 2

I changed all the ports to 2020 in the Naming.lookup() method and it executes fine. I thought this method took the server port number as an argument, not the Registry port number.