Right now there is only apply(JsonNode) -> JsonNode, which doesn't
really have the best Java integration. What would be nice would be to
return proper Java types. Unfortunately, we don't know what type the
user wants, so a general API is difficult. The user knows, however, so
we could make one method for each alternative.
That is, we could extend Expression with methods like these:
public String queryString(JsonNode input);
public Collection<String> queryStrings(JsonNode input);
public boolean queryBoolean(JsonNode input);
public int queryInt(JsonNode input);
public Collection<Integer> queryInts(JsonNode input);
public long queryLong(JsonNode input);
public Collection<Long> queryLongs(JsonNode input);
That should make it much easier to use the API in Java code.
Another possibility is to have a Jslt class which has direct methods
like:
public JsonNode apply(String query, JsonNode input);
public JsonNode queryString(String query, JsonNode input);
// ...
This saves the user from having to first compile and then apply the expression. The performance cost of doing compilation over and over again could be resolved by having a simple cache inside the class.