Java RemarshalException

Introduction to RemarshalException in Java

Distributed systems in Java often rely on remote method invocation and middleware frameworks like CORBA (Common Object Request Broker Architecture). CORBA allows objects running on different JVMs (or machines) to interact. However, communication over networks can be unstable, leading to retries and special handling. One such mechanism is RemarshalException.

This tutorial walks you through RemarshalException, what it means, when it’s thrown, and how to handle it using beginner-friendly examples. We’ll discuss it in the context of CORBA and distributed method calls, and even throw in some familiar analogies using apples, bananas, and cherries to make it sweet and simple.

What is RemarshalException?

RemarshalException is part of the CORBA (Common Object Request Broker Architecture) system in Java, specifically in the org.omg.CORBA.portable package. It is thrown internally by the ORB (Object Request Broker) during a remote invocation when a request must be retried or resent due to marshalling issues or failovers.

Class Hierarchy

java.lang.Object
 ↳ java.lang.Throwable
    ↳ java.lang.Exception
       ↳ org.omg.CORBA.portable.RemarshalException

When is RemarshalException Thrown?

This exception typically occurs in low-level CORBA stubs during communication failures that necessitate a re-marshalling (i.e., re-encoding) of the data before trying again.

Key scenarios include:

• Temporary connection loss
• Server failover or redirection
• Request needs to be re-sent due to protocol-level requirements

Understanding CORBA Context

Before diving into code, a quick primer: CORBA allows Java applications to invoke methods on remote objects using IDL (Interface Definition Language). These interfaces are compiled into Java stubs and skeletons. If a method invocation fails mid-communication, the stub might catch a RemarshalException and attempt to resend the request.

Example Setup

To demonstrate RemarshalException, we’ll mock the behavior of a CORBA client stub that encounters a re-marshalling situation during a banana count retrieval operation.

Example: Simulating RemarshalException in a CORBA-style Stub

package com.example.corba;

import org.omg.CORBA.portable.RemarshalException;

public class BananaRemoteStub {
    private int attempt = 0;

    public int getBananaCount() throws RemarshalException {
        System.out.println("Attempting to fetch banana count...");
        if (attempt == 0) {
            attempt++;
            throw new RemarshalException();
        }
        return 42;
    }
}

Client Code That Handles RemarshalException

package com.example.corba;

public class BananaClient {
    public static void main(String[] args) {
        BananaRemoteStub stub = new BananaRemoteStub();
        boolean success = false;
        int bananaCount = 0;

        while (!success) {
            try {
                bananaCount = stub.getBananaCount();
                success = true;
            } catch (org.omg.CORBA.portable.RemarshalException e) {
                System.out.println("RemarshalException occurred. Retrying...");
            }
        }

        System.out.println("Banana count received: " + bananaCount);
    }
}

Output

Attempting to fetch banana count...
RemarshalException occurred. Retrying...
Attempting to fetch banana count...
Banana count received: 42

Explanation

• The first attempt simulates a failure (such as temporary network glitch)
• RemarshalException is thrown by the stub
• The client catches it and retries the method call
• The second attempt succeeds and the banana count is printed

How Should You Handle RemarshalException?

Since this exception is used by CORBA’s internals, application developers usually don’t need to catch it themselves. It’s typically caught and handled within the autogenerated stubs. However, if you're writing low-level CORBA stub code or using CORBA in a custom setup, here’s what you should do:

• Retry the request safely and idempotently
• Log the occurrence for monitoring and debugging
• Limit retries to prevent infinite loops

Common Mistakes

Mistake	Fix
Retrying infinitely without a limit	Set a maximum number of retry attempts
Not logging or alerting on repeated exceptions	Implement monitoring around failed requests
Retrying non-idempotent operations	Ensure operations are safe to repeat

Best Practices

• Use proper retry mechanisms with backoff
• Design remote methods to be idempotent
• Gracefully degrade or notify users if repeated failures occur

Real-World Analogy

Imagine sending a letter to get your cherry count from a distant fruit warehouse. If your first letter is lost in transit, the post office automatically resends it. This automatic resend is like a RemarshalException—the system realized something went wrong mid-journey and needs to restart the conversation.

Recap

• RemarshalException is part of CORBA’s low-level retry logic
• It signals the need to re-send a request due to communication issues
• Handled mostly within CORBA stubs but can be caught in custom logic
• Retry logic must be safe and bounded to prevent runaway failures

Conclusion

While CORBA may not be at the forefront of modern Java development, understanding exceptions like RemarshalException is essential when working in enterprise systems that rely on legacy middleware.