JsonReader (C#): Non-cached, forward-only access to JSON data
Atif Aziz
I have added a JSON text parser, called JsonTextReader, that provides non-cached, forward-only access to JSON data. JsonTextReader [1] can be found in the Jayrock project from version 1.0.7507 onwards. I am mentioning it here in case other libraries may be interested in a similar approach.
Background:
When I originally started with the Jayrock project, I took off by porting the Java JSONTokener implementation [2] to C# and re-factored it such that it outputs the abstract JSON type system (embodied in IParserOutput) as opposed to specific classes like JSONObject [3] and JSONArray [4]. With JsonTextReader, I've got JSONTokener in the final form I had planned originally. JsonTextReader basically takes JSONTokener and turns its implementation into a yield/continuation approach where it does the heavy-lifting of running a state machine internally instead of requiring it from its users. With a non-caching and forward-only approach, JsonTextReader also allows you to rip through large JSON text without incurring the cost of building an in-memory object graph if all you're interested in is just some pieces of data. Here's an example that build a list of servlet names (see also full example in the test case called "Shred" [5]):
JsonReader reader = new JsonTextReader(
new StringReader(text));
ArrayList names = new ArrayList();
while (reader.Read())
{
if (reader.Token == JsonToken.Member &&
reader.Text == "servlet-name")
items.Add(reader.ReadString());
}
I noticed that JSONObject has been enhanced to be even more liberal in its lexical space, so I have updated the C# implementation similarly. I have also added a Jayrock-JSON solution/project for those who wish to use the JSON-only pieces of Jayrock without importing all the JSON-RPC baggage.
[2] http://www.json.org/javadoc/org/json/JSONTokener.html
[3] http://www.json.org/javadoc/org/json/JSONObject.html
[4] http://www.json.org/javadoc/org/json/JSONArray.html