How to properly convert List of specific objects to Gson?

gson, hibernate, java, json

Solution

I have resolved my problem. The assumption about `HibernateProxy` objects seemed to be very probable. However everything has started to work properly when I have read carefully my error. Finally I have registered type adapter in this way:

public String messagesToJson(List<Message> messages) {  
    GsonBuilder gsonBuilder = new GsonBuilder();
    Gson gson = gsonBuilder.registerTypeAdapter(Message.class, new MessageAdapter()).create();
    return gson.toJson(messages);
}

Any my `MessageAdapter` class looks like:

public class MessageAdapter implements JsonSerializer<Message> {

    @Override
    public JsonElement serialize(Message message, Type type, JsonSerializationContext jsc) {
        JsonObject jsonObject = new JsonObject();
        jsonObject.addProperty("message_id", message.getMessageId());
        jsonObject.addProperty("message", message.getMessage());
        jsonObject.addProperty("user", message.getUsers().getUsername());
        jsonObject.addProperty("date", message.getDate().toString());
        return jsonObject;      
    }
}

And thats all. Now I can get JSONs in jQuery using AJAX properly.

Problem

I am working on Spring MVC project. I am using Hibernate. I want to use AJAX with jQuery to get some JSONs from my Spring Controllers. Unfortunately when I was implementing `Gson` methods in my application I have got an error: ``` java.lang.UnsupportedOperationException: Attempted to serialize java.lang.Class: org.hibernate.proxy.HibernateProxy. Forgot to register a type adapter? ``` Which adapter I have to use and in which way? The error has occurred on the last line of the method: ``` public String messagesToJson(List<Message> messages) { Gson gson = new Gson(); List<Message> synchronizedMessages = Collections.synchronizedList(messages); return gson.toJson(synchronizedMessages, ArrayList.class); } ``` This is my `Message` class I am using in my Spring MVC project with Hibernate: ``` @Entity @Table(name = "MESSAGES", schema = "PUBLIC", catalog = "PUBLIC") public class Message implements java.io.Serializable { private static final long serialVersionUID = 1L; private int messageId; private User users; private String message; private Date date; //Constructor, getters, setters, toString } ``` EDIT I am wondering: my `Message` object is proxied or the whole `List<Message>`? I am getting the list of messages in this way: ``` public List<Message> findAllUserMessages(String username) { Query query = entityManager.createQuery("from Message where username = :username order by date desc") .setParameter("username", username); @SuppressWarnings("unchecked") List<Message> messages = query.getResultList(); return messages; } ``` EDIT 2 No, my `List<Message>` object isn't proxied.

Original source

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