CODEWITHSUNDEEP
javaserializationjvmstatic-membersdistributed-system
Gadam
Gadam

Reputation: 3024

How are calls to static members of another class handled in Java Object Serialization?

public class Employee implements java.io.Serializable
{
   public String name = "Tom"; 

   public void mailCheck()
   {
      String address = SomeClass.ItsStaticField(name);  //call to static

      System.out.println("Mailing a check to " + name
                           + " " + address);
   }
}

public class SomeClass()
{         
   // Static Map of <Name, Address>
   private static Map<String, String> NameAddressMap= new HashMap<String, String>();
   string address;

     Static ItsStaticField(name)
       {
          if (NameAddressMap.containsKey(name){
              address = NameAddressMap.get(name);
          }
          else{
            // address =...make a webservice call ... get address for name
            NameAddressMap.put(name, address);
          }
       return address;
       }
}

What happens when an object of the above is serialized? And deserialized on another node in a distributed environment? When is 'SomeClass.ItsStaticField()' invoked? Is the 'address' field's value calculated before serialization and then bundled into bytes as part of the serialization process?

Update: Apologize for taking the liberty to add some more info. Added sample code for 'SomeClass'. I have the above code in a distributed environment (specifically Hadoop). I understand this is a bad thing because there are going to be multiple web-service calls, and the intended 'caching mechanism' doesn't really work as expected. What I want to understand is, when and how many times the web-service call would be invoked? And how many instances of the static map 'NameAddressMap' is created on all nodes and when? Thanks much!

Upvotes: 0

Views: 87

Answers (3)

Giulio Franco
Giulio Franco

Reputation: 3230

When a class is serialized, the node deserializing it need all the .class files required for the deserialization. In your case, the class SomeClass is part of the dependencies of Employee. So, in order to deserialize an Employee, both Employee.class and SomeClass.class are required on the local node.

Note: due to Java being dynamically compiled, it should work until you actually try to call the mailCheck method.

Upvotes: 1

khelwood
khelwood

Reputation: 59210

Serialization serialises the objects fields, not its methods. The contents of the methods remain in the class definition, not in the instance itself.

Upvotes: 1

Peter Lawrey
Peter Lawrey

Reputation: 533820

What happens when an object of the above is serialized?

The name is serialized

And deserialized on another node in a distributed environment?

The name is deserialized

When is 'SomeClass.ItsStaticField()' invoked?

When you call mailCheck();

Is the 'address' field's value calculated before serialization and then bundled into bytes as part of the serialization process?

No, it is not a member of the object serialized.

Upvotes: 4

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