Java

dtrexp-java implements DTRExp in Java. Its scope is parsing, validation and coverage evaluation — the spec’s core interface; rendering, description and RRULE export are out of scope, the reference implementation has them. Pure Java 17+, zero dependencies (java.time for IANA zones), driven by the shared conformance vectors.

Install

Not on Maven Central yet. Build from source with ./run.sh; it compiles the sources under src/ and runs the conformance suite. The planned coordinate is io.onury:dtrexp.

Quick Start

import io.onury.dtrexp.DtrExp;
import java.time.Instant;

DtrExp dtr = DtrExp.parse("T0900:1800 E1:5");   // Mon–Fri, 09:00–18:00
// throws a positioned DtrExpParseException on a syntax or static-validity error

boolean open = dtr.covers(Instant.now(), "Europe/Berlin");
// —> true on a weekday, 09:00–18:00 Berlin local time

You parse once (at write/config time) and evaluate many. A DtrExp is immutable after parse and safe to share across threads; covers is a single calendar-field extraction followed by integer comparisons, with no occurrence iteration. toString() returns the source expression verbatim.

Examples

An access-control grant that only applies during business hours; the expression lives in the grant as data, and the check runs on every request:

import io.onury.dtrexp.DtrExp;
import java.time.Instant;

// grant.scope = "T0900:1800 E1:5"  — stored in your DB / ACL
DtrExp scope = DtrExp.parse(grant.scope());

boolean allowed = scope.covers(Instant.now(), user.zone());
// —> true inside Mon–Fri 09:00–18:00 in the user's zone, false outside it
if (!allowed) {
    throw new ForbiddenException("outside the permitted window");
}

The zone is an evaluation parameter, never part of the expression. Three covers overloads take it three ways:

dtr.covers(instant);                          // UTC — the default zone
dtr.covers(instant, ZoneId.of("Asia/Tokyo")); // a preloaded ZoneId
dtr.covers(instant, "Asia/Tokyo");            // an IANA identifier

Validation with the spec’s unsatisfiability lint; D30 M2 parses but can never match, and validate tells you so instead of failing silently:

ValidationResult res = DtrExp.validate("D30 M2");   // never throws
res.valid();       // —> true — it parses
res.warnings();    // —> [DtrExpWarning{position=…, message="unsatisfiable …"}]
                   //     no February has 30 days

Errors and warnings both carry a position; the 0-based character offset into the source, rendered into the message as (at N):

DtrExp.parse("Y*/3");   // anchorless stride — throws DtrExpParseException
// e.position() points at the offending character

API

Static Methods

Method	Description
`DtrExp.parse(String)`	Parses a DTRExp string into an immutable `DtrExp`, or throws a `DtrExpParseException` with a `position()` on a syntax or static-validity error. The only way to construct a `DtrExp`.
`DtrExp.validate(String)`	Non-throwing variant. Returns a `ValidationResult` record; typo-shaped input comes back as data, never an exception.

`DtrExp` Instance

Member	Description
`covers(Instant)`	Whether the expression covers the instant, evaluated in UTC. A single calendar-field extraction followed by integer comparisons.
`covers(Instant, ZoneId)`	Same, evaluated in a preloaded `ZoneId`.
`covers(Instant, String)`	Same, evaluated in a zone given as an IANA identifier.
`warnings()`	The §9.1 unsatisfiability warnings of the parsed expression; a `List<DtrExpWarning>`, same content as `validate(s).warnings()`.
`toString()`	The source expression, verbatim.

Records and Exceptions

Type	Description
`ValidationResult`	Record with `valid()` `boolean`, `errors()` (parsing stops at the first syntax error, so at most one `DtrExpParseException`) and `warnings()` `List<DtrExpWarning>`.
`DtrExpWarning`	Record of `(int position, String message)`.
`DtrExpParseException`	Thrown by `parse` on invalid input; carries a `position()` `int` and the message.

The zone is always an evaluation parameter, never part of the expression. Its default is UTC. DST is handled per spec §9.3: spring-forward gap times cover nothing; repeated fall-back times are covered on both passes.

Quality

The test suite is driven by the shared vectors.json from the spec repo: every coverage, rejection, warning and quiet vector, including the calendar traps (Feb 29 across 2000/2024/2100, W53 existence, DST gap/overlap in Europe/Berlin). The vectors are vendored at test/resources/vectors.json; see VECTORS.md for how the suite works. The build compiles under javac -Xlint:all -Werror, so a warning fails it. Zero dependencies.