JSON output : not returning empty string but empty json array instead

[ghetolay]

On QidoRS when there is no match for a request a empty body is returned which is a problem when client expect a JSON result.
An empty string is invalid JSON and breaks on most system, returning an empty array instead '[]' is correct JSON and is less error prone.

From json.org :

JSON is built on two structures:

- A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.
- An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.

So a json message can't be just a string (empty or not) it can only be an object {...} or array [...]
( some system allows nullas well).

Example of system rejecting empty string as JSON :

• Javascript function JSON.parse() consider an empty string as invalid JSON and throws error
• Java JsonParser (glassfish implementation) also throws an exception with the message :
  Expected tokens are: [CURLYOPEN, SQUAREOPEN]
  (Didn't test myself but qido-client is also most likely affected by this)

Now even if some implementation accept empty string as valid JSON it's safer to return an empty array.

About code change :

For XML output I kept the return of empty string by returning a null entity when no match are found (javax.ws.rs.core.Response.ResponseBuilder.entity(Object)accepts null as argument).

[ghetolay]

Ho ok didn't know there was an active jira. What's the url ? The one mentioned on the readme brings to a project with no issue so I thought this was not used.

Next time I'll look into it before.

About the implementation I don't know what you exactly mean by tackle but I think writeXML is the real problem here. Problem which was covered with theses lines on the search function :

if (!query.hasMoreMatches())
    return Response.ok().build();

It seems more logical to me that output.entity() returns the correct entity (null, empty, text, multipart etc..) rather than bypassing the call on some condition. And writeXML(), as it is, returns a multipart entity when there is no match rather than no entity.

What I don't like on my fix is the use of count which is a variable used for debug logging purpose (realized that later). So maybe a global if would be better like :

private Object writeXML(Query query, QueryRetrieveLevel qrlevel) {
    if(query.hasMoreMatches())
        MultipartRelatedOutput output = new MultipartRelatedOutput();
        int count = 0;
        while (query.hasMoreMatches()) {
            ....
       }
        return output;
    } else 
        return null;
}