GWT Serialize Ordering/Comparator of TreeMap

Question

I have a serializable object with a TreeMap.

Map<String, Dogs> dogsByNames = Maps.newTreeMap(); // guava style

So far, everything is fine. Now it's nessassary to ignore the case of the keys:

Map<String, Dogs> dogsByNames = Maps.newTreeMap(String.CASE_INSENSITIVE_ORDER);

This do not work because String.CASE_INSENSITIVE_ORDER isn't serialzable:

com.google.gwt.user.client.rpc.SerializationException: Type 'java.lang.String$CaseInsensitiveComparator' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = java.lang.String$CaseInsensitiveComparator@f26f68

So I create my own one:

private static abstract class MyComparator<T>
    implements
        Comparator<T>, // extends Ordering<T> do not work
        IsSerializable { // Serializable do not work
}

public static final MyComparator<String> CASE_INSENSITIVE_ORDER = new MyComparator<String>() {
    @Override
    public int compare(final String left, final String right) {
        if (null == left) {
            return (null == right) ? 0 : -1;
        } else if (null == right) {
            return 1;
        }
        return left.compareToIgnoreCase(right);
    }
};

But this still do not work.

Whats wrong?

Solution:

protected static class MyOrdering // no-private!!!
    extends
        Ordering<String>
    implements
        IsSerializable {
    @Override
    public int compare(final String left, final String right) {
        if (null == left) {
            return (null == right) ? 0 : -1;
        } else if (null == right) {
            return 1;
        }
        return left.compareToIgnoreCase(right);
    }
}

public static final Ordering<String> CASE_INSENSITIVE_ORDER = new MyOrdering();

Answer 1

The CASE_INSENSITIVE_ORDER you created is an anonymous class, which cannot be serialized in GWT. To make it GWT serializable, you need to

1. Create a custom top-level class (like

   CaseInsensitiveOrder implements Comparator<..>, Serializable {
       ...
   }
   

2. Create a constant CASE_INSENSITIVE_ORDER like you did.

3. Create a custom field serializer for that class (CaseInsensitiveOrder_CustomFieldSerializer), which returns the CASE_INSENSITIVE_ORDER instance on deserialize().