Learning Java

Simple Serialized Object Protocols

Earlier in this chapter, we showed a hypothetical conversation in which a client and server exchanged some primitive data and a serialized Java object. Passing an object between two programs may not have seemed like a big deal at the time, but in the context of Java as a portable byte-code language, it has profound implications. In this section, we’ll show how a protocol can be built using serialized Java objects.

Before we move on, it’s worth considering network protocols. Most programmers would consider working with sockets to be “low-level” and unfriendly. Even though Java makes sockets much much easier to use than many other languages, sockets still provide only an unstructured flow of bytes between their endpoints. If you want to do serious communications using sockets, the first thing you have to do is come up with a protocol that defines the data you’ll be sending and receiving. The most complex part of that protocol usually involves how to marshal (package) your data for transfer over the Net and unpack it on the other side.

As we’ve seen, Java’s DataInputStream and DataOuputStream classes solve this problem for simple data types. We can read and write numbers, Strings, and Java primitives in a recognizable format that can be understood on any other Java platform. But to do real work, we need to be able to put simple types together into larger structures. Java object serialization solves this problem elegantly, by allowing us to send our ...