Problems with Collection serialization

[Vijaishanker bala]

hi,

I am trying to serialize a collection of objects like in

 ObjectProgram program1 = new ObjectProgram("vijai"); 
       ObjectProgram program2 = new ObjectProgram("vijai");
ArrayList coll = new ArrayList();
coll.add(program1);
coll.add(program2);
coll.add(program1);
coll.add(program2);
coll.add(program1);
coll.add(program2);
coll.add(program1);
coll.add(program2);
coll.add(program1);
coll.add(program2);
coll.add(program1);
coll.add(program2);
try {
System.out.println(coll.size());
ObjectOutputStream out = new ObjectOutputStream(
new FileOutputStream("d:/objects.xml"));
out.writeObject(coll);
out.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
} 

but when i open the created file, it appears as if only the last object is written, the remaining objects in the collection are not written...And when deserializing it asks to be deserialized as an object of type "ObjectProgram" and not an object of type "ArrayList"...Is there any other better way to serialize and deserialize a collection of objects using standard java apis. yes,"ObjectProgram" implements Serializable

thanks

Vijai

[Ernest Friedman-Hill]

This should be fine. Let's see the de-serialization code.

[Vijaishanker bala]

the code for Deserialization is as follows,

  ObjectInputStream in = new ObjectInputStream(new FileInputStream(
"d:/objects.xml"));
 Collection newColl = (Collection) in.readObject();
in.close();
 

The error thrown for this code is

java.io.InvalidClassException: com.vijai.matrix.plugin.Schema.ObjectProgram; no valid constructor
at java.io.ObjectStreamClass.<init>(ObjectStreamClass.java:379)
at java.io.ObjectStreamClass.lookup(ObjectStreamClass.java:253)
at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:453)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1521)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1435)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1626)

[Vijaishanker bala]

The full code is as follows, the previous code snippets were taken at different times...contradicted between the serializing and Deserializing
This is the actual code

ObjectProgram program1 = new ObjectProgram("vijai");
      ObjectProgram program2 = new ObjectProgram("vijai");
ArrayList coll = new ArrayList();
coll.add(program1);
coll.add(program1);
coll.add(program1);
coll.add(program2);
coll.add(program1);
coll.add(program2);
coll.add(program1);
 
try {
 
//Serialize Part
 System.out.println(coll.size());
 ObjectOutputStream out = new ObjectOutputStream(
 new FileOutputStream("d:/objects.xml"));
 out.writeObject(coll);
 out.close();
//Deserialize Part
 ObjectInputStream in = new ObjectInputStream(new FileInputStream(
"d:/objects.xml"));
 ArrayList newColl = (ArrayList) in.readObject();
in.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}  

[Ernest Friedman-Hill]

You don't show the code for the class "ObjectProgram", but one of the requirements for deserialization of a class is that the superclass must either be Serializable itself, or must have a no-argument constructor. The error message is telling you that deserialization failed for an instance of ObjectProgram, not that the entire file contains a single ObjectProgram. Although the message isn't clear, I suspect what this is saying is that ObjectProgram's superclass is not serializable, and doesn't have a default constructor.

[Vijaishanker bala]

Thanks Earnest,

It solved my problem. As a matter of fact, the derived class had a serializable implementation while the Super class did not have one.When I made the superclass to implement Serializable it worked fine.

Vijai