A small, embeddable JSON query engine for Java, built on Gson and designed for high‑throughput systems such as MAPS Messaging.

This implementation is inspired by jsonquerylang, but is intentionally constrained:

• No mutation
• No scripting
• No runtime eval
• Compile once, execute many

Filtering is powered by MAPS’ JMS selector parser, giving you a proven predicate language instead of inventing yet another one.

• Gson‑native (JsonElement everywhere)
• Compile JSON query ASTs into executable functions
• Stable sorting
• Selector‑based filtering (JMS selectors)
• Deterministic, side‑effect‑free execution
• Pluggable function registry

Supported functions:

• get
• filter
• sort
• map
• pick
• pipe

JsonQueryCompiler compiler = JsonQueryCompiler.createDefault();

JsonElement query = JsonParser.parseString("""
["pipe",
  ["filter", "address.state = 'Alaska'"],
  ["sort", ["get","age"], "desc"],
  ["pick", "first", "age"]
]
""");

Function<JsonElement, JsonElement> program = compiler.compile(query);

JsonElement input = JsonParser.parseString("""
[
  {"first":"Chris","age":23,"address":{"state":"Alaska"}},
  {"first":"Joe","age":32,"address":{"state":"Alaska"}},
  {"first":"Emily","age":19,"address":{"state":"Texas"}}
]
""");

JsonElement result = program.apply(input);

Queries are expressed as JSON ASTs, not strings.

["get", "age"]

["filter", "address.state = 'Alaska'"]

["sort", ["get","age"], "desc"]

["map", ["get","age"]]

["pick", "name", "age"]

["pipe",
  ["filter", "state = 'Alaska'"],
  ["sort", ["get","age"], "desc"],
  ["pick", "name", "age"]
]

Filtering uses the MAPS JMS selector parser, so predicates like these are supported:

state = 'Alaska'
age >= 21
address.state IN ('Alaska','Texas')

Selectors are compiled once and evaluated per element.

Add your own functions without touching the compiler:

Map<String, JsonQueryFunction> custom = new HashMap<>();
custom.put("myFn", new MyFunction());

JsonQueryCompiler compiler =
    JsonQueryCompiler.create(FunctionRegistry.builtIns(),
                             new FunctionRegistry(custom));

Each function lives in its own class and implements:

JsonQueryFunction

• Predictable execution
• Explicit null handling
• Zero reflection
• No hidden magic
• Broker‑safe performance characteristics

This is a query/filter engine, not a programming language.

Apache License 2.0 with Commons Clause

See LICENSE for details.