Java JSON Parser

This is a very minimalistic JSON parser I wrote to practice Java. Use in production at your own risk (:

The parser works as a very basic state machine that uses either expected tokens or termination tokens to proceed to the next state.

Warning

The master branch is the active development branch and my be unstable compared to the releases.

If you're looking for a more "stable" version, check the releases.

Current Features

• Can parse String, int, double, boolean, Object (nested JSON), null and Array values.
• Modifying/creating JSON (JsonResult) objects/arrays
• Writing JSON objects/arrays to string

Upcoming Features

• Reflection to parse a JSON directly into a user-defined class

Known Issues

• Parser may break if keys or values contain escaped quotes

Basic Usage

You can also take a look at the tests, but here's some basic usage of the library:

Parsing Single Objects

JsonParser parser = new JsonParser();
String jsonString = """
    {
        \"key\": {
            \"innerKey\": 10
        },
        \"key2\": 1.23,
        \"key3\": \"Hello, world!\",
        \"key4\": null,
        \"key5\": [1, 2.2, [1, 2, 3], { \"inner key\": \"inner value\"}, false],
        \"key6\": true
    }
    """;
JsonResult result = parser.parse(jsonString);

// retrieve values
int innerKey = result.getObject("key").getInt("innerkey"); // 10
double key2 = result.getDouble("key2"); // 1.23
String key3 = result.getString("key3"); // Hello, world!
boolean key4 = result.isNull("key4"); // true
boolean key6 = result.getBoolean("key6"); // true

// handling arrays
JsonArray key5 = result.getArray("key5");
int arrayValue1 = key5.getInt(0); // 1
double arrayValue2 = key5.getDouble(1); // 2.2
JsonArray arrayValue3 = key5.getArray(2); // [1, 2, 3]
JsonResult arrayValue4 = key5.getObject(3); // { "inner key": "inner value" }
boolean arrayValue5 = key5.getBoolean(4); // false

// overwrite values
// overwrites key2 from 1.23 -> "hello"
result.setValue("key2", new JsonItem("hello", JsonType.STRING));

// add new values
result.addString("newkey", "new value");
result.addInt("intkey", 12);

Keys and values must use DOUBLE quotes and NOT single quotes!

DO NOT use get() methods to check if a value is null since this will return null if the key is not present in JSON. Use the isNull() method instead.

Parsing Arrays

If given an array of JsonObjects (or primitives), you can parse the arrays directly.

String arrayString = """
[
    {\"key\": 1},
    {\"key\": 2},
    {\"key\": 3}
]
""";

JsonArray array = JsonArray.fromString(arrayString);
array.getObject(0).getInt("key"); // 1
array.getObject(1).getInt("key"); // 2
array.getObject(2).getInt("key"); // 3

// overwrite value (changes 2 -> 42)
array.getObject(1).setValue("key", new JsonItem(42, JsonType.INTEGER));

// add value
array.addString("hello"); // [ 1, 42, 3, "hello" ]
array.addNull(); // [ 1, 42, 3, "hello", null ]

Writing to String

Both objects (JsonResult) and arrays (JsonArray) have a toString() method to convert either representation to a string.

Building

• Run ./gradlew build from the root directory
• A jar file will be found in ./lib/build/libs/json-parser-[VERSION].jar
  • [VERSION] is the version of the library you're building.