Create object from byte array (with constructor)

Question

In my project I have a class which often needs to be serialized to byte array. I currently have a constructor in my class which takes the array, parses it and creates a new object. Once it is done, the constructor reads needed fields from that (new) object and sets appropriate values in the class.

public class MyClass implements Serializable {
  private int fieldOne;
  private boolean fieldTwo;
  ...

  // This is default constructor
  public MyClass(){
  }

  // This is the constructor we are interested in
  public MyClass(byte[] input){
    MyClass newClass = null;

    try(ByteArrayInputStream bis = new ByteArrayInputStream(input);
         ObjectInput in = new ObjectInputStream(bis)) {
          newClass = (MyClass) in.readObject();
      } catch (ClassNotFoundException | IOException e) {
          e.printStackTrace();
      }
    if (newClass != null) {
      this.fieldOne = newClass.getFieldOne;
      this.fieldTwo = newClass.getFieldTwo;
      ...
    }
  }

  public int getFieldOne(){
    return fieldOne;
  }
  public boolean getFieldTwo(){
    return fieldTwo;
  }
  ...
}

Code like this works correctly, but the question is: Is it possible to create (with that constructor) MyClass object directly, without creating that "newClass" instance and setting all values manually?

Why do you need it to be a constructor? You could just make it a static method and simply return newClass. — Paul Boddington
– Paul Boddington, Commented Mar 18, 2016 at 12:39

wero · Accepted Answer · 2016-03-18 12:41:03Z

1

No this is not possible.

But instead of a constructor MyClass(byte[]) which then creates two MyClass objects, you can introduce a static factory method:

public static MyClass create(byte[] input) {
    try(ObjectInput in = new ObjectInputStream(new ByteArrayInputStream(input))) {
        return (MyClass)in.readObject();
    }
    catch (Exception e) {
        throw new IllegalStateException("could not create object", e);
    }
}

answered Mar 18, 2016 at 12:41

wero

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Comments

epoch · Accepted Answer · 2016-03-18 12:39:54Z

You should not be deserializing your object like that, rather implement readObject as the specification indicates:

private void readObject(ObjectInputStream in)
    throws IOException, ClassNotFoundException {

    in.defaultReadObject();

    // custom
    this.fieldOne = in.readXXX();
    this.fieldTwo = in.readXXX();
}

And this is specifically for custom serialization, why don't you use the api directly, or make a static method for retrieving an object:

public static MyClass readFromByteArray(byte[] input) {
    Myclass obj = null;

    try (ByteArrayInputStream bis = new ByteArrayInputStream(input);
        ObjectInputStream ois = new ObjectInputStream(bis)) {
        obj = (MyClass) in.readObject();
    } catch (ClassNotFoundException | IOException e) {
        e.printStackTrace();
    } 

    return obj;   
}

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