A JSON parsing abstraction built over the existing JSONParser in Salesforce to simplify extracting values (no need to create a class to serialise to).
I built this when making many HTTP callouts to an API returning many different JSON formatted responses. I only wanted one or two values from each response so it made no sense to build classes for these responses. Using the basic JSONParser in Salesforce is a nightmare iterating through the different tokens, working out where you are in the token tree.
So now you can just create this serialiser and call get() to find your key in the JSON object. get() only does a shallow scan of the parent object and always returns a JSONField. You then access the value from the Value property (Value is null if the key was not found). If your key is multiple objects deep then you can recursively call get() to access the key walking down the object tree. If the value for a key is an object or array then it will be returned as a string.
If you need to access an array, first return the array string from your key. Then call Util_JSONParser.parseArray() passing in your array as a string. This method returns a list of Util_JSONParser. You can then iterate through these parsers, accessing the keys as usual.
###Usage:
String jsonContent = '{' +
' "someKey": "someValue",' +
' "anotherKey": true,' +
' "aKeyWithObject": {' +
' "moreValues": "foo"' +
' },' +
' "anArray": [' +
' {' +
' "bar": true,' +
' "baz": "yes"' +
' },' +
' {' +
' "bar": false,' +
' "baz": "banana"' +
' }' +
' ]' +
'}';
Util_JSONParser parser = Util_JSONParser.createParser(jsonContent);
String value1 = parser.get('someKey').Value; // returns 'someValue'
String value2 = parser.get('anotherKey').Value; // returns 'true'
String value3 = parser.get('notPresentKey').Value; // returns Null
String value4 = parser.get('aKeyWithObject').get('moreValues').Value; // returns 'foo'
String value5 = parser.get('aKeyWithObject').Value; // returns '{"moreValues":"foo"}'
String arrayString = parser.get('anArray').Value; // returns '[{"bar":true,"baz":"yes"},{"bar":false,"baz":"banana"}]'
List<Util_JSONParser> arrayParser = Util_JSONParser.parseArray(arrayString);
for (Util_JSONParser p : arrayParser) {
String value6 = p.get('bar').Value; // returns 'true' for first object, 'false' for second
}