A Java 21 library that compiles JSONata expressions into native Java classes at runtime. Each expression is parsed, optimised, and translated to Java source, which is then compiled in-memory and returned as a ready-to-call JsonataExpression instance. Repeated evaluation of a JsonataExpression instance is significantly faster than interpreter-based alternatives — around 56× faster than JSONata4Java on a realistic analytical benchmark.

All test cases from the official JSONata test suite pass.

This is the compiler behind valem.run’s reactive engine — every derived field in its 100+ live tax and cost models is a JSONata expression compiled through this library.

The same pipeline exists for JavaScript and Python — see Sibling implementations.

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Requirements

Requirement	Version
Java	21 (JDK — a JRE is not sufficient; the in-memory compiler needs javac)
Jackson Databind	2.18+
joni	2.2+ (Oniguruma regex engine — used for /pattern/flags literals and the $match, $replace, $split, $contains functions)

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Getting started

1. Add the dependency

<dependency>
    <groupId>io.github.vlad-public-code</groupId>
    <artifactId>jsonata-jvm-compiler</artifactId>
    <version>1.0.6</version>
</dependency>

2. Compile an expression

JsonataExpressionFactory factory = new JsonataExpressionFactory();
JsonataExpression expr = factory.compile("Account.Order.Product.Price * 1.2");

compile() runs the full pipeline once and returns a reusable, thread-safe object. Compile expressions at startup and reuse them for every request — do not call compile() on the hot path.

Compiling many expressions at once

When you need to compile a group of expressions up front (e.g. every derivation, constraint, and effect of a model at registration time), use compileAll instead of calling compile in a loop:

List<JsonataExpression> exprs = factory.compileAll(List.of(
        "Account.Order.Product.Price * 1.2",
        "$sum(items.price)",
        "status = \"active\""));

compileAll returns one JsonataExpression per input, in order, and each behaves exactly as if produced by compile. The difference is cost: the pipeline runs the expensive javac step once for the whole batch rather than once per expression. That step is dominated by a fixed per-invocation overhead (compiler bootstrap, platform symbol loading, classpath indexing) that a single small generated class barely adds to, so batching many expressions is dramatically faster than compiling them one at a time — around 10× for 20 expressions in the project’s own benchmark (JsonataBatchCompilationPerfTest). The saving is one fixed javac cost per batch instead of one per expression, so how large it is depends on how many expressions the batch holds. Parsing and translation still happen per expression, so a syntactically invalid entry is reported with its index; any failure aborts the whole batch with a JsonataCompilationException.

3. Evaluate against JSON

ObjectMapper mapper = new ObjectMapper();
JsonNode input = mapper.readTree("""
    {
      "Account": {
        "Order": {
          "Product": { "Price": 50.0 }
        }
      }
    }
    """);

JsonNode result = expr.evaluate(input);  // → 60

evaluate() accepts a Jackson JsonNode and returns a JsonNode. The same JsonataExpression instance can be evaluated concurrently from multiple threads.

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Exception types

Exception	When thrown
JsonataCompilationException	compile() — the expression is syntactically invalid or (rarely) the generated code fails to compile
JsonataEvaluationException	evaluate() — the input is not valid JSON, or the expression cannot be applied to it (type mismatch, division by zero, etc.)

try {
    JsonataExpression expr = factory.compile(expression);
    JsonNode result = expr.evaluate(json);
} catch (JsonataCompilationException e) {
    // bad expression — e.getCause() is a ParseException with source position
} catch (JsonataEvaluationException e) {
    // bad input JSON or runtime error
}

---

JSONata language features

The library implements all JSONata language features, functions as first-class values included: a function can be stored in a variable, put in an array or object, passed to and returned from another function, and carried across the binding boundary in either direction — see Functions as values.

Bindings

Bindings let you inject named values and Java functions into an expression at runtime. Inside the expression they are referenced as $name (values) or called as $name(args...) (functions).

Per-evaluation bindings

Pass a JsonataBindings instance as the second argument to evaluate() to supply values or functions for a single call:

JsonataExpression expr = factory.compile("$taxRate * subtotal");

ObjectMapper mapper = new ObjectMapper();
JsonNode input = mapper.readTree("{\"subtotal\": 500}");
JsonNode taxRate = mapper.readTree("0.2");

JsonataBindings bindings = new JsonataBindings()
        .bindValue("taxRate", taxRate);

JsonNode result = expr.evaluate(input, bindings);  // → 100

Per-evaluation bindings are not stored on the expression instance and do not affect other calls.

Permanent bindings

Use assign() and registerFunction() to attach bindings permanently to an expression instance. They apply to every subsequent evaluate() call.

JsonataExpression expr = factory.compile("$round2($taxRate * subtotal)");

// Permanent value
ObjectMapper mapper = new ObjectMapper();
expr.assign("taxRate", mapper.readTree("0.2"));

// Permanent function
expr.registerFunction("round2", new JsonataBoundFunction() {
    @Override
    public String getFunctionSignature() { return "<n:n>"; }

    @Override
    public JsonNode apply(JsonataFunctionArguments args) {
        double v = args.get(0).doubleValue();
        return new DoubleNode(Math.round(v * 100.0) / 100.0);
    }
});

JsonNode r1 = expr.evaluate(mapper.readTree("{\"subtotal\": 100}"));  // → 20.0
JsonNode r2 = expr.evaluate(mapper.readTree("{\"subtotal\": 333}"));  // → 66.6

Permanent bindings are isolated per instance — assigning to one JsonataExpression does not affect any other.

Precedence

When both a permanent binding and a per-evaluation binding exist for the same name, the per-evaluation binding wins.

Functions as values

A bound function is not only callable — $name on its own is a function value, so it can be passed to a higher-order built-in, piped through ~>, or handed to another bound function:

JsonataBindings bindings = new JsonataBindings().bindFunction("double", doubler);

factory.compile("$map([1,2,3], $double)").evaluate(input, bindings);   // → [2, 4, 6]
factory.compile("5 ~> $double").evaluate(input, bindings);             // → 10
factory.compile("$type($double)").evaluate(input, bindings);           // → "function"

This is what makes a library export usable as an argument as well as a call target, since exports are supplied through registerFunction.

The reverse also holds: a function value can be bound with bindValue and called by name. JsonataRuntime.lambdaNode builds one from a Java lambda, with the number of parameters it takes:

JsonNode timesTen = JsonataRuntime.lambdaNode(x -> new DoubleNode(x.doubleValue() * 10), 1);

JsonataBindings bindings = new JsonataBindings().bindValue("f", timesTen);

factory.compile("$f(3)").evaluate(input, bindings);          // → 30.0
factory.compile("$map([1,2], $f)").evaluate(input, bindings); // → [10.0, 20.0]

Both maps are consulted, and the one that matches the position wins: $name in value position prefers a value binding, $name(...) at a call site prefers a function binding.

Arity. How many arguments reach a bound function used as a value is decided by its declared signature — <nn:b> makes a two-argument function, so $sort([2,3,1], $desc) receives a comparator pair and $map supplies the index. A signature that does not pin the arity down (absent, unparseable, or variadic) yields a one-argument function value. This is the same limitation hand-written JSONata lambdas have: a packed argument tuple is an array, and so is a single array argument. Declare a fixed arity to receive several arguments.

Implementing JsonataBoundFunction

JsonataBoundFunction has two methods:

Method	Purpose
String getFunctionSignature()	Describes the expected argument types and return type (see signature syntax below)
JsonNode apply(JsonataFunctionArguments args)	Executes the function; may throw JsonataEvaluationException

JsonataFunctionArguments wraps the argument list. Accessing an out-of-range index returns MissingNode rather than throwing.

Function signature syntax

The signature has the form <params:return> where params is a sequence of type symbols and return is a single type symbol.

Simple types

Symbol	Type
b	Boolean
n	number
s	string
l	null

Complex types

Symbol	Type
a	array
o	object
f	function
j	any JSON type — equivalent to (bnsloa)
u	Boolean, number, string, or null — equivalent to (bnsl)
x	any type at all, functions included — equivalent to (bnsloaf)
(sao)	union: string, array, or object

Parametrised types: a<s> (array of strings), a<x> (array of any type), f<n:n> (a function from number to number). A parametrised f requires a function, but the argument function’s own parameter and return types are not checked — jsonata-js does not check them either.

An argument declared f that is not a function is rejected with T0410. Note that j is documented by the JSONata spec as excluding functions but does not reject one here; declare f when you require a function.

Option modifiers appended to a type symbol:

Modifier	Meaning
+	One or more arguments of this type (variadic)
?	Optional argument
-	Use the context value (“focus”) if the argument is missing

Example: $length has signature <s-:n> — accepts a string (using context as focus if omitted) and returns a number.

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JSONata libraries

The bindings above are written in Java: a JsonataBoundFunction per function, an assign per value, repeated for every expression that needs them. A library is the same set of bindings written in JSONata instead — once, in one file — and applied to any expression that needs it.

A library is nothing more than a definition expression: ordinary JSONata that binds names and returns the names to export.

(
  $vatRate := 0.2;
  $round2  := function($n){ $round($n, 2) };
  $gross   := function($net){ $round2($net * (1 + $vatRate)) };
  $format  := function($n){ "£" & $string($round2($n)) };

  ["gross", "format", "vatRate"]
)

That is a complete, valid JSONata expression. Evaluate it in any JSONata engine and it returns ["gross", "format", "vatRate"] — the export list is the expression’s result, not a parameter passed from Java. So a definition file can be linted, tested and run by tools that know nothing about this library, and it states its own interface: nothing outside it decides what it provides.

JsonataLibrary billing = factory.compileLibrary(definition);

billing.getFunctions();   // Map<String, JsonataBoundFunction> — gross, format
billing.getConstants();   // Map<String, JsonNode>             — vatRate

Each exported name lands in one map or the other according to what it evaluated to — the definition never says which is which. Names it binds but does not export ($round2 here) stay private, while remaining reachable from the exported functions.

Providing bindings from a library

useLibrary applies a whole library, functions and constants together, so the caller never has to know which name is which. On the expression it is permanent, for the lifetime of that instance:

JsonataExpression invoice = factory.compile("lines.$gross(amount) ~> $sum() ~> $format()");

invoice.useLibrary(billing);

or per evaluation, when different calls need different libraries:

JsonataBindings bindings = new JsonataBindings()
        .useLibrary(billing);

invoice.evaluate(input, bindings);

It returns the same JsonataBindings, so libraries and one-off bindings compose in a single expression:

JsonataBindings bindings = new JsonataBindings()
        .useLibrary(billing)
        .useLibrary(formatting)
        .bindValue("today", today);

Applying two libraries that export the same name leaves the later one in place, exactly as re-binding a name always does.

Either way the expression sees $gross(...), $format(...) and $vatRate exactly as if they had been written in Java — the precedence rules above apply unchanged, so a per-evaluation binding still wins over a library one registered permanently.

Applying a library to every expression in an application is one line each:

for (JsonataExpression expr : factory.compileAll(expressions)) {
    expr.useLibrary(billing);
}

What a definition can contain

Anything JSONata can express. Exported functions may be recursive, mutually recursive, closures over private helpers, λ-notation, functions returned by other functions, ~> chains, or partial applications:

(
  $pi := 3.1415926535897932384626;

  /* private helpers — not exported, still reachable */
  $product   := function($a, $b) { $a * $b };
  $factorial := function($n) { $n = 0 ? 1 : $reduce([1..$n], $product) };

  $sin := function($x){ $cos($x - $pi/2) };
  $cos := function($x){
    $x > $pi ? $cos($x - 2 * $pi) : $x < -$pi ? $cos($x + 2 * $pi) :
      $sum([0..12].($power(-1, $) * $power($x, 2*$) / $factorial(2*$)))
  };

  ["sin", "cos", "pi"]
)

Constants are values, not expressions: the definition runs once, when the library is compiled, so $total := $sum([1..10]) exports the number 55. Functions, by contrast, run whenever they are called.

The export list is itself an expression — ["sin", "cos"] is the usual form, a single "sin" works, and so does a list computed at definition time. A definition that forgets its export list ends on its last binding and therefore returns a function; that is rejected with must return an array of function names.

Exported functions can also be called straight from Java, with no expression involved:

JsonataBoundFunction gross = billing.getFunctions().get("gross");
JsonNode result = gross.apply(new JsonataFunctionArguments(List.of(DoubleNode.valueOf(100))));

Signatures

Each exported function reports a JSONata signature:

Definition	Reported signature
$twice := function($x)<n:n>{ $x * 2 }	<n:n> — the declared one
$volume := function($l, $w, $h){ ... }	<j?j?j?:j> — synthesised, all-optional
$normalize := $uppercase ~> $trim	none — arity known only at call time

The synthesised form is deliberately permissive: JSONata lets a lambda be called with fewer arguments than it declares (the rest are undefined), and j applies no coercion — so an exported function accepts exactly what the same function accepts inside JSONata. Ask for something stricter with a signature override:

JsonataLibrary lib = factory.compileLibrary(definition,
        new JsonataLibraryOptions().signature("$gross", "<n:n>"));

// "<n:n>" coerces at the boundary: $gross("100") works

Lifetime and options

A library owns one generated class, so build it once at startup and keep it — the same advice as compile(). Exported functions are thread-safe and may be called concurrently.

JsonataLibrary is AutoCloseable; close() retires the exported functions (calling one afterwards throws JsonataEvaluationException), which is only worth doing when the lifetime should be explicit. Constants keep working — they are ordinary nodes. Letting the library become unreachable releases everything.

JsonataLibraryOptions also carries the document the definition is evaluated against (input, for a definition that reads from data) and the bindings visible while it runs (bindings).

A definition must be self-contained

Every name a definition uses has to come from somewhere it controls: a name it binds itself, a JSONata built-in, or a name handed to it at build time. Anything else is rejected when the library is compiled:

($withVat := function($net){ $net * (1 + $vatRate) }; ["withVat"])

→ JsonataCompilationException: The definition expression uses $vatRate, which it does not bind
  and which is not a JSONata built-in. Bind it in the definition, or supply it through
  JsonataLibraryOptions.bindings.

The alternative — resolving $vatRate against whatever happens to be bound where $withVat is called — would make a library’s behaviour depend on its caller, and would make a typo ($rat for $rate) indistinguishable from a deliberate hook. Failing at build time names both the problem and the fix.

To parameterise a library, supply the values when you build it:

JsonataLibrary lib = factory.compileLibrary(definition,
        new JsonataLibraryOptions().bindings(
                new JsonataBindings().bindValue("vatRate", rate)));

Those names are then in scope for the definition, and are captured by the functions it exports.

Lambda parameters, bindings inside nested blocks, forward references between siblings (mutual recursion), and path bindings (@$v, #$i) all count as bound — only genuinely unresolvable names are reported.

One further semantic worth knowing: the caller’s evaluation is reused. Called from inside an expression, an exported function shares that evaluation’s recursion budget (100 nested calls) and its setTimeout deadline.

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Advanced usage

Evaluation timeout

Call setTimeout(int timeoutMs) on an expression instance to cap how long a single evaluate() call may run. If the deadline is exceeded, a JsonataEvaluationException with error code U1001 is thrown.

JsonataExpression expr = factory.compile("...");
expr.setTimeout(500);   // 500 ms wall-clock limit per evaluate() call

try {
    JsonNode result = expr.evaluate(input);
} catch (JsonataEvaluationException e) {
    if ("U1001".equals(e.getErrorCode())) {
        // evaluation exceeded 500 ms
    }
}

Pass 0 or a negative value to remove the timeout. The timeout applies to all future evaluate() calls on the instance; concurrent calls on the same instance each track their own independent deadline. Setting a timeout has no measurable overhead on evaluations that complete before the deadline.

Inspecting the source expression

JsonataExpression expr = factory.compile("$sum(items.price)");
System.out.println(expr.getSourceJsonata());  // → "$sum(items.price)"

Accessing the generated Java source

Use the lower-level API to obtain the generated source before compilation:

import org.json_kula.jsonata_jvm.parser.Parser;
import org.json_kula.jsonata_jvm.optimizer.Optimizer;
import org.json_kula.jsonata_jvm.translator.Translator;
import org.json_kula.jsonata_jvm.parser.ast.AstNode;

AstNode ast = Optimizer.optimize(Parser.parse("price * qty"));
String javaSource = Translator.translate(ast, "com.example.gen", "PriceExpression", "price * qty");
System.out.println(javaSource);

Loading a pre-generated Java class

If you have previously generated and saved a Java source string, compile it directly without re-parsing:

import org.json_kula.jsonata_jvm.loader.JsonataExpressionLoader;

JsonataExpressionLoader loader = new JsonataExpressionLoader();
JsonataExpression expr = loader.load(javaSource);

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Performance

jsonata-jvm-compiler compiles expressions to native JVM bytecode, so repeated evaluation is significantly faster than interpreter-based alternatives.

Benchmark: jsonata-jvm-compiler vs JSONata4Java

The benchmark compiles one expression once, then runs 100,000 evaluations against the same JSON document (with a 1,000-evaluation JVM warmup before timing). The expression is a realistic analytical query covering variable bindings, nested field navigation, array filtering, aggregation functions ($sum, $count, $average, $max, $min, $distinct), string operations, arithmetic, and a conditional.

Measured on OpenJDK 21 (Temurin 21.0.10), Windows 11. The figures come from the side-by-side test, which warms up and times both libraries in one JVM. Treat the round numbers as the useful precision — they are the range across four runs on 2026-09-05: 131,313 / 131,332 / 135,529 / 136,597 eval/s, at 55.0× / 54.9× / 58.9× / 57.9×.

The speedup does not track our own throughput exactly, because the ratio moves with JSONata4Java’s as well: its 2,302–2,392 eval/s across the same four runs is the steadier of the two, but it is not constant, so the fastest run here is not quite the highest ratio.

Metric	jsonata-jvm-compiler	JSONata4Java
Compilation	~790–1,120 ms	~150–320 ms
100,000 evaluations	~730–760 ms	~41,800–43,400 ms
Throughput	~131,000–137,000 eval/s	~2,300–2,390 eval/s
Speedup	~55×–59× faster	baseline

These are higher than the ~126,000–129,000 eval/s the same test reported on 2026-09-04, and the gain is real rather than machine drift: widening the sequence-scan fusion pass — it now absorbs !=, and/or and the four ordering comparisons inside a predicate, which this benchmark uses in several places — measured +5% to +17%, in the same direction in all six runs of a paired A/B with both builds compiled in one session. Absolute throughput on this machine drifts by more than that between sessions, which is why the attribution comes from the paired comparison rather than from these numbers.

Compilation is a one-time cost paid at startup. For any workload that reuses an expression more than a handful of times, the throughput advantage dominates. Compiling several expressions? Use compileAll — one javac invocation for the batch instead of one per expression, worth around 10× for 20 expressions.

Where the speed comes from, beyond compiling to bytecode: literal values are hoisted to static fields rather than rebuilt inside every loop; object constructors with literal keys are filled into two parallel arrays with no hashing and no duplicate check, since the compiler already knows the keys are distinct; common aggregate shapes ($count(x[field = "value"]), $sum(x.field)) are fused into a single loop with no intermediate sequence; the several operations a block performs over one sequence are then fused again into a single pass that reads each field once per element rather than once per operation; and the runtime’s hot type checks are single dispatches rather than chains of megamorphic calls.

The benchmark is reproducible via:

mvn test -Dtest=PerformanceComparisonTest -DargLine="-Djunit.jupiter.conditions.deactivate=org.junit.jupiter.engine.extension.DisabledCondition"

The benchmark class carries @Disabled so that a normal mvn test does not spend minutes on it, which is why the run needs that condition switched off — selecting the test with -Dtest= alone silently skips it.

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Thread safety

A JsonataExpressionFactory instance and all JsonataExpression instances it produces are fully thread-safe. evaluate() is stateless — each call processes the input JSON independently and returns a new JsonNode without modifying any shared state.

// Compile once at startup
JsonataExpression totalPrice = factory.compile("$sum(items.(price * qty))");

// Call concurrently from any number of threads
ExecutorService pool = Executors.newFixedThreadPool(16);
pool.submit(() -> totalPrice.evaluate(requestJson));

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Architecture

expression string
       │
       ▼
  Parser.parse()                   → AstNode (sealed interface hierarchy)
       │
       ▼
  Optimizer.optimize()             → AstNode (constant-folded, simplified)
       │
       ▼
  Translator.translate()           → Java 21 source string
       │
       ▼
  JsonataExpressionLoader.load()   → JsonataExpression (compiled, in-memory)
       │
       ▼
  expr.evaluate(json)              → JsonNode

JsonataExpressionFactory.compile() runs this entire pipeline in a single call.

Package structure

Package	Contents
org.json_kula.jsonata_jvm	Public API: JsonataExpression, JsonataExpressionFactory, JsonataBindings, JsonataBoundFunction, JsonataFunctionArguments, JsonataCompilationException, JsonataEvaluationException
org.json_kula.jsonata_jvm.parser	Parser, ParseException
org.json_kula.jsonata_jvm.parser.lexer	Lexer, Token, TokenType
org.json_kula.jsonata_jvm.parser.ast	AstNode sealed interface with all node types and Visitor
org.json_kula.jsonata_jvm.optimizer	Optimizer
org.json_kula.jsonata_jvm.translator	Translator
org.json_kula.jsonata_jvm.runtime	JsonataRuntime (static helper methods), JsonataLambda
org.json_kula.jsonata_jvm.loader	JsonataExpressionLoader, JsonataLoadException

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Sibling implementations

The same parse → optimise → translate → compile pipeline exists for three host runtimes:

Runtime	Project	Host code it generates	Speedup vs. that runtime’s reference interpreter
JVM	jsonata-jvm-compiler (this project, Java 21) — docs · Maven Central · source	Java source, compiled in-memory by javac	~56× vs JSONata4Java
JavaScript	jsonata2js — docs · npm · source	a JS function, loaded with new Function	~53×–60× vs jsonata
Python	jsonata2py — docs · PyPI · source	Python source, compiled by the host compile()	~54× vs jsonata-python

Each figure is the one that project measures against its own runtime’s reference interpreter, on its own benchmark and its own hardware; they are not comparable across rows. All three pass the official JSONata test suite.

The JVM implementation is the original, and is the compiler behind valem.run’s reactive computation engine.

Conformance is also worked on across all three together: when one port disagrees with the reference (jsonata 2.2.2, the arbiter), the other two are run before concluding anything, because “every reimplementation gets this wrong” is a different finding with a different fix from “this port gets this wrong”. That has repeatedly changed the diagnosis — and each port’s write-up has corrected an earlier one’s.

License

This project is licensed under the Apache License 2.0.

See also

• tracked-json — Jackson JsonNode wrapper that tracks each node’s location (JsonPointer) and document root through every navigation — get, path, at, parent(), and JSONPath (RFC 9535). Includes JSON Patch (RFC 6902).
• Valem — deterministic reactive computation runtime for AI-generated structured data models.
• Valem Sandbox