I'm using JSON-lib to parse an object and read a string from it. This works fine for a valid string but it can also be null. For example:
JSONObject jsonObject = JSONObject.fromObject("{\"foo\":null}");
String str = jsonObject.getString("foo");
In this case I would expect str to be null but it is instead "null". Calling any other method seems to throw an error. Is there anyway to have JSONLib parse a string if the value is a string but return null if the value is null?
JSONObject.java:
/**
* Get the string associated with a key.
*
* @param key A key string.
* @return A string which is the value.
* @throws JSONException if the key is not found.
*/
public String getString( String key ) {
verifyIsNull();
Object o = get( key );
if( o != null ){
return o.toString();
}
throw new JSONException( "JSONObject[" + JSONUtils.quote( key ) + "] not found." );
}
You can see that getString() never return null. It can return "null" if o.toString() do that but this will be String not null value
I couldn't find a nice way to do this, so I did switch to Jackson instead. This allows me to do:
JsonNode json = (new ObjectMapper()).readValue("{\"foo\":null}", JsonNode.class);
json.get("stopType").getTextValue();
Which will return null for this example, as expected.
It's a bug of JSONLib which has been reported .
https://github.com/douglascrockford/JSON-java/issues/5
Upgrading your jsonlib to latest version will probably fix it.
Why not make use of JSONObject::opt? You'll get a null (not "null") if the key doesn't exist.
String str = (String) jsonObject.opt("foo");
.getString(), which returns aString, and you expected something other than a string?