Sending and Receiving Serialized Objects in Java - Socket Programming

Question

(I know this can be done in RMI, but I need to do this using sockets since I found there could be some setup process if RMI methods used)

Please have a look at the simple Client-Server code at http://www.coderanch.com/t/205325/sockets/java/send-any-java-Object-through

In this program, the order two objects sent by SimpleServer are known by SimpleClient.

i.e: Server

oos.writeObject(new testobject(1,"object from client")); oos.writeObject(new String("another object from the client"));

Client does the casting according to the order the object is received.But I want to avoid this nature and make client send any object at any time so the server should also be able to handle each object sent accordingly and return a result.

testobject to = (testobject)ois.readObject(); 
System.out.println(to.id);}  
System.out.println((String)ois.readObject());

Is there a way to "label" the objects being sent so that the action can be determined by a simple "if" statement in Server?

OR

is there a better way to use a ResultSet returned by the Server instead of my object serializing approach?

thanks in advance.

Thanks

The objects you read with ObjectInputStream already have the correct runtime type - casting doesn't change it. So in a way they're already "labelled", you can call getClass() or use instanceof on them and handle them according to that. — millimoose
– millimoose, Commented Sep 21, 2011 at 19:21
Don't use new String("another object from the client") its almost always pointless. — Peter Lawrey
– Peter Lawrey, Commented Sep 21, 2011 at 20:34

Dan · Accepted Answer · 2011-09-21 19:23:41Z

2

readObject will return an object in its proper class. if you need to have some branching logic based on that you can use instanceof:

Object newObj = stream.readObject();
if (newObj instanceof testobject) {
     doSomething((testobject) newObj);
} else if (newObj instanceof String) {
     doSomethingWithString((String) newObj);
} // etc.

As a rule, this is not recommended for all objects read from a stream. If you're going to use ObjectStreams to establish a protocol, you should document it and stick to it. That way, if one side sends incorrect data, you'll catch it more quickly on the other side.

However, in a scenario where at a given point in the protocol flow, it's expected that the client might be sending one of several different types of objects, then it might make sense.

answered Sep 21, 2011 at 19:23

Dan

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2 Comments

coder9 Over a year ago

Thanks for the reply. I'll be using such approach to implement an ATM simulator where user will send PIN, Card No from a Client program to a Server. Server will validate those data and if valid, show his Account details. I hope to send these Account Details as objects to the client. What's your idea about this?

Miserable Variable Over a year ago

I have an excellent server in Nigeria through which can handle this kind of traffic very efficiently

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