Presents your  
JAVA E-NEWSLETTER for October 30, 2003 
 
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CUSTOMIZE SERIALIZATION BEHAVIOR FOR YOUR CLASSES   
  
When you're serializing Java objects, there are times when you may want to
avoid serializing certain properties of your Java class. When it comes to
avoiding the serialization of specific class members, you have three choices:
declare the field transient; provide a list of class members that should be 
serialized; or handle the actual reading and writing of instance data yourself.   
  
The easiest method for preventing serialization is to simply specify the
class property as transient. When a Serializable class property is 
marked as transient, the property will not be written to or read from an
instance's serialized stream. Here's an example of declaring a field transient:   
  
private transient long timestamp;   
  
It doesn't get much easier than that.   
  
The second way to control which fields get serialized is to define the 
field serialPersistentFields for your class. When you define this field in 
your Serializable class, only the classes described with entries in this

field will be serialized and deserialized when the object is written to 
and read from the object's byte stream. Telling Java what data should be
persistent, rather than what data fields shouldn't, is the opposite of 
the transient declaration.   
  
The third way is to take over the task of writing and reading object 
state yourself. A class that is Serializable but not Externalizable only
needs to provide the methods writeObject() and readObject(). When these 
methods are called, the class itself can decide which information 
should be serialized and which should not. An Externalizable class can
also implement the methods readExternal() and writeExternal() to override 
the object's serialization behavior.   
  
Java's object serialization mechanism gives the programmer wide latitude
in determining which properties of a class to serialize. The solutions 
range from simply adding a keyword to taking full responsibility for 
storing data. Explore all of your serialization options before deciding on a 
game plan to choose the right approach for your applications.   
  
David Petersheim is a Senior Java Developer with Genscape, Inc. He 
designs and develops server-side applications to acquire and process
real-time energy data.   

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