GWT Serialize Ordering/Comparator of TreeMap
guava, gwt, java, serialization, treemap
Solution
The CASE_INSENSITIVE_ORDER you created is an anonymous class, which cannot be serialized in GWT. To make it GWT serializable, you need to
Create a custom top-level class (like
CaseInsensitiveOrder implements Comparator<..>, Serializable {
...
}
Create a constant `CASE_INSENSITIVE_ORDER` like you did.
- Create a custom field serializer for that class (`CaseInsensitiveOrder_CustomFieldSerializer`), which returns the `CASE_INSENSITIVE_ORDER` instance on `deserialize()`.
Problem
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(); ```