ArrayList throwing exception on retrieval from google datastore (with gwt, java)

Question

I'm using Google Web Toolkit with java and google datastore as database. The entity class has arraylist and on trying to retrieve the data from data base I'm getting the exception:

Type 'org.datanucleus.sco.backed.ArrayList' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.

I'm using JPA.

Entity code:

 package com.ver2.DY.client;

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

 import javax.jdo.annotations.IdGeneratorStrategy;
 import javax.jdo.annotations.PersistenceCapable;
 import javax.jdo.annotations.Persistent;
 import javax.jdo.annotations.PrimaryKey;

 import com.google.gwt.user.client.rpc.IsSerializable;

 @PersistenceCapable
 public class ChatInfo implements Serializable, IsSerializable{
  @PrimaryKey
  @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
  private Long topicId;

  @Persistent
  private String chatTopic;

  @Persistent
  private ArrayList<String> messages = new ArrayList<String>();

  @Persistent
  private boolean isFirstPost;

  public ChatInfo()
  {

  }


  public Long getTopicId() {    
   return topicId;
  }
  public void setTopicId(Long topicId) {
   this.topicId = topicId;
  }
  public String getChatTopic() {
   return chatTopic;
  }
  public void setChatTopic(String chatTopic) {
   this.chatTopic = chatTopic;
  }
  public ArrayList<String> getMessages() {
   return messages;
  }
  public void addMessage(String newMsg) {
    messages.add(newMsg);
  }

  public boolean isFirstPost() {
   return isFirstPost;
  }
  public void setFirstPost(boolean isFirstPost) {
   this.isFirstPost = isFirstPost;
  }

 }

Method in db class:

@Transactional
  public ChatInfo[] getAllChat() {
   PersistenceManager pm = PMF.get().getPersistenceManager();
   List<ChatInfo> chats = null;
   ChatInfo[] infos = null;
   String query = "select from " + ChatInfo.class.getName();
   try{
    chats = (List<ChatInfo>) pm.newQuery(query).execute();


   infos = new ChatInfo[chats.size()];
   for(int i=0;i<chats.size();i++)
   {
    infos[i] = new ChatInfo();
    infos[i] = (ChatInfo) chats.get(i);
   }
   }
   finally{
    pm.close();
   }
   return infos;

  }

It is a bit strange because earlier I was able to insert and retrieve the data but it now throwing an exception. On searching the web I could find that I need to convert the Arraylist from some DataNucleus type to java util but not sure how to do that.

Answer 1

The exception is caused by the fact that the class is not in your GWT RPC whitelist (list of classes which are serializable).

I am unable to see any import of the org.datanucleas.sco.backed.ArrayList in any of the example code you have given.

Check out this question for more info on GWT and JPA.