Problems with GWT and Enum

Question

I have an enum in the client part of a GWT application and I am getting an exception when I try to run it that is related to serialization problems. Am I doing anything wrong? I read that enums are supported by GWT and I am using the last version.

The enum:

public enum AnEnum implements Serializable {

    ITEM_A("Item a description"), ITEM_B("Item b description");

    private String description;

    private AnEnum(String description) {
        this.description = description;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

}

The exception:

Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeWithCustomSerializer(ServerSerializationStreamWriter.java:742)
    ... 47 more
Caused by: com.google.gwt.user.client.rpc.SerializationException: Type '(...).client.(...).AnEnum' 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.: instance = ITEM_A
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:610)
    at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:129)
    at com.google.gwt.user.client.rpc.core.java.util.Collection_CustomFieldSerializerBase.serialize(Collection_CustomFieldSerializerBase.java:43)
    at com.google.gwt.user.client.rpc.core.java.util.LinkedList_CustomFieldSerializer.serialize(LinkedList_CustomFieldSerializer.java:36)
    ... 52 more

Answer 1

Add IsSerializable interface, a default scoped no-arg constructor, and make sure its in one of the paths listed in the source tags in your gwt.xml file. <source path="client">

I really think the third suggestion is the issue; I remember having this issue before and it was because I had a dto outside the source paths.

You can have multiple source tags.

<source path="common" />
<source path="client" />

One pattern is to put persisted objects directly under com.mysite.common, and mashups of persisted items that get transferred over the wire in com.mysite.common.dto, and of course the client gui code is in client.

package com.mysite.client;

import java.io.Serializable;

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

public enum AnEnum implements Serializable, IsSerializable {

    ITEM_A("Item a description"), ITEM_B("Item b description");

    private String description;

    AnEnum() {
    }

    AnEnum(String description) {
        this.description = description;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

}