The documentation for Struts2 plugin version 2.3.x says that the includeProperties parameter can be set, and behaves as follows:
A comma-delimited list of regular expressions can be passed to the JSON Result to restrict which properties will be serialized. ONLY properties matching any of these regular expressions will be included in the serialized output.
However, from my own testing, this doesn't appear to be the case. At any rate, it does not seem to support full regex syntax as one might expect (i.e. the full set of expressions that would work with java.util.regex.Pattern).
Take a simple example where we might want to use the greedy optional quantifier ("?") with a group. To make things concrete, this pattern: ^(items\\[\\d+\\]\\.)?userName$ does not work; it is ignored and your includeProperties ends up being null.
But if you instead just use ^items\\[\\d+\\]\\.userName$ then it works (the pattern is recognized and added). Looking through org.apache.struts2.json.JSONUtil source shows that there is a lot of custom code written to process the patterns.
It's not mentioned in the JSON plugin documentation that only a special subset of regex is supported. What is the story on which types of expressions are supported or not supported by this plugin?
