Exceptions allowed while implementing readObject and writeObject method to override default serialization in java?

Question

I know that we have to define methods with the following signatures to override the default serialization process:

private void writeObject(ObjectOutputStream os) {
}

private void readObject(ObjectInputStream is) {
}

Are there any restrictions on the type of exceptions which can be thrown by the above methods? I know that exceptions thrown by a method are not part of method signature but wanted to confirm.

Answer 1

Serializable defines the following exceptions:

private void writeObject(java.io.ObjectOutputStream out)
    throws IOException
private void readObject(java.io.ObjectInputStream in)
    throws IOException, ClassNotFoundException;
private void readObjectNoData()
    throws ObjectStreamException;

---

This is where the write method gets called:

        try {
            writeObjectMethod.invoke(obj, new Object[]{ out });
        } catch (InvocationTargetException ex) {
            Throwable th = ex.getTargetException();
            if (th instanceof IOException) {
                throw (IOException) th;
            } else {
                throwMiscException(th);
            }
        }

// ...

private static void throwMiscException(Throwable th) throws IOException {
    if (th instanceof RuntimeException) {
        throw (RuntimeException) th;
    } else if (th instanceof Error) {
        throw (Error) th;
    } else {
        IOException ex = new IOException("unexpected exception type");
        ex.initCause(th);
        throw ex;
    }
}

As you can see you can throw any non-runtime exception and it will be wrapped in an IOException, though you should prefer IOExceptions due to shorter stack traces and more useful error messages.

I assume the read method gets called similarly, you might want to check it yourself though.

Answer 2

You can throw any RuntimeException in both Methods

In writeObject(ObjectOutputStream out) you can also throw IOException

In readObject(ObjectInputStream in) yu can also throw IOException and ClassNotFoundException