使用 Java RMI 传递复合对象

Question

I need to send a medication plan for the client using RMI. The server and client are in separate projects, both have these classes defined (entities and the remote interface):

public class Plan implements Serializable {
    private Integer id;
    private Date periodStart;
    private Date periodEnd;
    private Integer patientId;
    private Medication medications;
}

public class Medication implements Serializable {
    private Integer id;
    private String name;
    private Integer dosage;
    private Integer intakeInterval;
}

public interface PillService extends Remote {
    public Plan getPlan(int id) throws RemoteException;
}

The code above works fine, but i need to have a list of medications in the Plan like this:

 public class Plan implements Serializable {
        ...
        private List<Medication> medications;
    }

If i run with this Plan class, i get this exception:

Client exception: java.rmi.UnmarshalException: error unmarshalling return; nested exception is: 
    java.lang.ClassNotFoundException: org.hibernate.collection.internal.PersistentBag (no security manager: RMI class loader disabled)

After this I added SecutiryManager to System i get error:

java.security.AccessControlException: access denied ("java.net.SocketPermission" "127.0.0.1:1099" "connect,resolve")
    at java.security.AccessControlContext.checkPermission(AccessControlContext.java:472)

So, it works fine without List<Medication> in the Plan . Doesn't RMI like composite objects? Should i define a new remote method for getting the list of medications separately?

Answer 1

The problem appears to be the runtime type of your List . The class is not available from the client end, so RMI is trying to download the code from the remote codebase. This has quite reasonably been disabled.

The easiest fix would be to use a well known implementation for List . Copy the list either where it is set in Plan or in a custom writeObject method.

this.medications = new ArrayList<>(medications);

Or

  private void writeObject(
     ObjectOutputStream out
  ) throws IOException {
     this.medications = new ArrayList<>(this.medications);
     out.defaultWriteObject();
  }

It looks like you List is a lazy loading implementation, so this will force it to be entirely loaded. You might be able to simply use eager loading.

Ideally, don't use RMI including the Java Serialization part.