GWT - DataObject was not serializable and has no concrete serializable subtypes

[Dennis van Beek]

Hi, I've been working with GWT for a few weeks now, but now I have a big problem.

I'm using a DataObject to transport my objects from the database to the client.
So all my objects extend this DataObject.
This was working fine, until I tried to replace all the String-fields in the DataObject by a new class called 'DataAttribute'

This DataAttribute is nothing more than a class with 4 Strings ->
one representing the database-fieldname, one representing the 'readable' fieldname, one representing the value and one that can be used for a special display-value (used for foreign keys).

Now I can't start my webapp anymore, it gives this message for all my Objects;

[ERROR] Type 'weerribben.client.objects.DataAttribute' was not serializable and has no concrete serializable subtypes

The DataAttributes are stored in an ArrayList the DataObject-class, and are initialized in the implementing classes;


This is my DataAttribute;

package weerribben.client.objects;

import java.io.Serializable;

import weerribben.client.helper.ObjectHelper;

public class DataAttribute implements Serializable {
	
	/** A default serialVersionUID */
	private static final long serialVersionUID = 1L;

	private String databaseField, displayName;
	private String value;
	private String displayValue;
	
	/**
	 * @param databaseField The database fieldname
	 * @param displayName The displayable name
	 */
	public DataAttribute(String databaseField, String displayName) {
		this.databaseField = databaseField;
		this.displayName = displayName;
		value = "";
		displayValue = null;
	}
	
	/**
	 * @param databaseField ...
	 */
	public DataAttribute(String databaseField) {
		this.databaseField = databaseField;
		this.displayName = ObjectHelper.formatToGUI(databaseField);
		value = "";
		displayValue = null;
	}
	
	/**
	 * @return the databaseField
	 */
	public String getDatabaseField() {
		return databaseField;
	}

	/**
	 * @param databaseField the databaseField to set
	 */
	public void setDatabaseField(String databaseField) {
		this.databaseField = databaseField;
	}

	/**
	 * @return the displayName
	 */
	public String getDisplayName() {
		return displayName;
	}

	/**
	 * @param displayName the displayName to set
	 */
	public void setDisplayName(String displayName) {
		this.displayName = displayName;
	}

	/**
	 * @return the value
	 */
	public String getValue() {
		return value;
	}

	/**
	 * @param value the value to set
	 */
	public void setValue(String value) {
		this.value = value;
	}

	/**
	 * @return the displayValue
	 */
	public String getDisplayValue() {
		
		if (displayValue == null) { 
			return value;
		}
		return displayValue;
	}

	/**
	 * @param displayValue the displayValue to set
	 */
	public void setDisplayValue(String displayValue) {
		this.displayValue = displayValue;
	}
}

And this is my DataObject (sorry for the dutch comments);

package weerribben.client.objects;

import java.io.Serializable;
import java.util.ArrayList;

public abstract class DataObject implements Serializable {

	/** Een default SerialVersionUID */
	private static final long serialVersionUID = 1L;
	
	/** De DataAttribute-lijst met alle beschikbare attributen voor dit object */
	private ArrayList<DataAttribute> allFields = new ArrayList<DataAttribute>();
	
	/** De DataAttribute-lijst met alle zoek-velden */
	private ArrayList<DataAttribute> searchableFields = new ArrayList<DataAttribute>();
	
	/** De DataAttribute-lijst met alle velden voor in de resultaatlijsten */
	private ArrayList<DataAttribute> showableFields = new ArrayList<DataAttribute>();
	
	
	/**
	 * De initialisatie van dit object
	 */
	public DataObject() {
		initialize(searchableFields, showableFields, allFields);
	}
	
	
	/**
	 * @return Een DataAttribute-Set met alle attributen waarop gezocht moete kunnen worden
	 */
	public final ArrayList<DataAttribute> getSearchableFieldNames() {
		return searchableFields;
	}
	
	/**
	 * @return Een ArrayList met alle DataAttribute die zichtbaar moeten zijn in resultaat-tabellen e.d.
	 */
	public final ArrayList<DataAttribute> getShowableFieldNames() {
		return showableFields;
	}
	
	/**
	 * @return Een HashMap met alle velden en bijbehorende waardes
	 */
	protected final ArrayList<DataAttribute> getAllFields() {
		return allFields;
	}
	
	/* The abstract methods */
	
	/**
	 * @return De unieke identificatie voor deze instantie
	 */
	public abstract Long getIdentifier();

	/**
	 * @param field Het veld die de waarde krijgt
	 * @param value De waarde die het veld moet krijgen
	 */
	public abstract void setValue(String field, String value);
	
	/**
	 * @return Ee nieuwe instantie van deze class
	 */
	public abstract DataObject createNew();
	
	/**
	 * @param searchableFields De velden waarop gezocht moet kunnen worden
	 * @param showableFields De velden die getoond moeten worden
	 * @param allFields Alle attributen voor dit object
	 */
	protected abstract void initialize(
			ArrayList<DataAttribute> searchableFields,
			ArrayList<DataAttribute> showableFields,
			ArrayList<DataAttribute> allFields);
}

This is how I implement the intitalize-method;

...

	/**
	 * {@inheritDoc}
	 * @see DataObject#initialize(ArrayList, ArrayList, ArrayList)
	 */
	protected void initialize(ArrayList<DataAttribute> searchableFields,
			ArrayList<DataAttribute> showableFields,
			ArrayList<DataAttribute> allFields) {
	
    	//Creating the DataAttributes
    	artikelnummer = new DataAttribute("artikelnummer");
    	artikelnaam = new DataAttribute("artikelnaam");
    	voorraadHoeveelheid = new DataAttribute("voorraad_hoeveelheid");
    	eindproduct = new DataAttribute("eindproduct");
    	
    	//Populating the lists
    	showableFields.add(artikelnummer);
    	showableFields.add(artikelnaam);

    	searchableFields.add(artikelnummer);
    	searchableFields.add(artikelnaam);
    	searchableFields.add(eindproduct);
		
    	allFields.add(artikelnummer);
    	allFields.add(artikelnaam);
    	allFields.add(voorraadHoeveelheid);
    	allFields.add(eindproduct);
	}

...

Can anybody tell me what I'm doing wrong, or how I can find the problem??

[Bear Bibeault]

"Online Metalhead", please check your private messages for an important administrative matter.

[Dennis van Beek]

I (finally) found the answer!

I forgot the default constructor in DataAttribute (which offcourse is needed for serialisation)!
(And I recently passed my SCJP, how could I forget?!?!)

More info; Blog with the answer