Implementing User-Defined Objects in Java Clients

Implementing User-Defined Objects in Java Clients

You can use one of two methods to implement a user-defined object in a Java client that works with C++ clients: Instantiator.register and DataSerializable.


With the Instantiator.register method, a client sends a RegistrationMessage to every Java VM in its distributed system. The message announces the mapping between a user-defined classId and class name. The other JVMs can deserialize the byte array with the correct class.

If two clients are in different distributed systems, a RegistrationMessage cannot be sent between them. For example: a put made by a client in one distributed system will hang when a client in another distributed system performs a get in pure Java mode. Similarly, a put made by a C++ client will cause a Java client to hang.


Using the DataSerializable method, the user-defined object is serialized into the following byte array:
45 <2-byte-length> <class-name>

A Java client can deserialize the byte array, but a C++ client cannot convert the Java class name to a C++ class name.


The DataSerializable method does not support using a nested object, while Instantiator.register does support the use of nested objects. A workaround is to let each Java client manually initiate an object for each possible user object class a C++ client provides, using the following code:
User u = new User("", 0);

See Java Serialization Example for a code sample that shows how to set up user object classes in a Java client.