A fast json parser (and builder), written in java.
photo: yoann supertramp [CC-BY]
- efficient — allocates as few objects as possible
- easy to use — simple api, inspired by minimal-json
- fast — like a bat out of hell!
the following chart shows benchmark results for parsing a 72K sample file on my macbook pro (2,7 ghz intel core i5).
flatjson outperforms some popular json parsers (gson, jackson) by 2x to 3x, and is even faster than boon (which is known to be pretty fast).
normally, we want to do something with json, once we've parsed it. the second benchmark simulates an event processing use case: parse the event, process the data (= reverse an array which makes up the bulk of the json document), then serialize the result back to a string.
as the graph shows, flatjson shines even more here.
you can run these benchmark yourself with ./gradlew jmh — a full run takes a bit over an hour.
flatjson does not build a parse tree, just an index overlay, which is stored in an integer array. json nodes are constructed on demand (= on first access). this way, lots of objects allocations are saved.
when serializing json, flatjson handles unchanged subtrees by copying substrings directly from input to output, bypassing actual serialization as much as possible.
flatjson is on Maven Central, simply add it as a gradle dependency:
compile 'org.zalando:flatjson:1.1.0'
Json json = Json.parse("[42, true, \"hello\"]");we can check which type of entity the returned Json object represents:
json.isNumber(); // --> false
json.isObject(); // --> false
json.isArray(); // --> truefor each isFoo method, there is a matching asFoo accessor.
arrays are represented by lists of Json objects.
List<Json> array = json.asArray();
array.size(); // --> 3
array.get(0).asLong(); // --> 42
array.get(1).asBoolean(); // --> true
array.get(2).asString(); // --> "hello"this list is mutable and allows manipulation of the json DOM:
array.add(Json.value(false));
json.toString(); // --> "[42,true,\"hello\",false]"you can also build objects from scratch:
Json test = Json.object();
Map<String, Json> object = test.asObject();
object.put("color", Json.value("blue"));
object.put("size", Json.value(39));
test.toString(); // --> "{\"color\":\"blue\",\"size\":39}"same with arrays:
Json test = Json.array();
List<Json> array = test.asArray();
array.add(Json.value("hello"));
array.add(Json.value(42));
test.toString(); // --> "[\"hello\",42]"contributions are welcome — especially
- reporting bugs
- running the benchmarks in different environments (AMD, Azure, AWS, Google Cloud ...) and sharing the results
- adding your favorite json parser to the benchmarks — can it beat flatjson?
- adding more unit tests.
i will not easily be persuaded to merge in major new features, though.
- implemented
Visitorpattern to interact with json - added
json.prettyPrint()(implemented asVisitor) json.equals()now based onjson.prettyPrint()
- support additional number types:
int,float,BigInteger,BigDecimal
- initial public release
The MIT License (MIT)
Copyright (c) 2017 Zalando SE
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