AISmessages

AISmessages is a lightweight, zero-dependency Java library for decoding NMEA-armoured AIS messages used in maritime navigation and safety systems.

It is built for production workloads: fast decoding, immutable message objects, predictable behavior under load, and a small footprint that fits comfortably into high-throughput or real-time systems.

Performance highlights (Apple M2 Max, single thread, JMH AverageTime)

Stage	ns/op	Throughput
NMEA sentence parse (new NMEAMessage)	~351 ns	~2.9 M sentences/sec
AIS payload decode (AISMessageFactory.create)	~112 ns	~8.9 M decodes/sec
Bit-field read (e.g. MMSI, lat/lon)	~0.9 ns	>1 billion reads/sec

Decoded messages are fully immutable — safe to share across threads with zero synchronisation overhead. The internal binary representation keeps retained heap per decoded message 3–6× lower than String-based approaches, keeping GC pauses short even at high message rates.

Why teams choose AISmessages

• Zero runtime dependencies for simple deployment and fewer surprises
• High performance with eager parsing and packed bit-level decoding
• Low memory footprint per message to keep GC pressure down
• Immutable value objects that are safe to share across threads
• Broad protocol coverage for standard AIS messages and supported application-specific messages
• Simple integration from InputStream, UDP, sockets, or your own NMEA pipeline
• Proven in production for more than 15 years

If you are new to AIS, start with What is AIS?.

Quick start

Add AISmessages from Maven Central:

<dependency>
    <groupId>dk.tbsalling</groupId>
    <artifactId>aismessages</artifactId>
    <version>VERSION</version>
</dependency>

Replace VERSION with the latest stable release from Maven Central.

Then decode AIS messages directly from an InputStream:

import dk.tbsalling.aismessages.AISInputStreamReader;

import java.io.InputStream;

public class DemoApp {
    public static void main(String[] args) {
        InputStream inputStream = ...;

        AISInputStreamReader reader = new AISInputStreamReader(
                inputStream,
                aisMessage -> System.out.println(aisMessage)
        );

        reader.run();
    }
}

AISInputStreamReader is the easiest entry point for most applications. Feed it NMEA sentences and it calls your consumer with decoded AISMessage instances.

What you get

AISmessages handles the full decoding path from NMEA framing to strongly typed AIS message objects:

1. Reads NMEA AIS sentences from streams or other sources
2. Validates and reassembles fragmented messages
3. Decodes 6-bit armoured AIS payloads
4. Produces immutable Java objects for the concrete AIS message types

Each AIS message type is represented by its own class, making the decoded data easy to consume in application code.

For example, a type 5 message is represented as ShipAndVoyageData, exposing fields such as IMO number, callsign, ship name, ship type, and vessel dimensions.

Performance

AISmessages is designed to stay fast and predictable when message rates climb.

• The architecture uses eager parsing and immutable value objects, so each decoded message is fully populated once and safe to pass to any thread without defensive copying.
• Structural validation reuses pre-compiled patterns and lookup tables — no unnecessary allocations on the hot path.
• The internal binary representation avoids String-based bit handling and keeps memory usage low.
• Retained heap per decoded message is roughly 3× lower for typical payload sizes and up to 6× lower for large payloads compared to String-based approaches.

JMH benchmarks (Apple M2 Max, Java 21, single thread, AverageTime mode — lower is better):

Benchmark	ns/op	~msg/sec
NMEAMessageParseBenchmark.parseOne	350.9	~2.9 M
AISMessageFactoryBenchmark.decodeOne	111.8	~8.9 M
BitStringMicroBenchmark.getUnsignedInt (30-bit MMSI)	0.86	>1 B
BitStringMicroBenchmark.getSignedInt (28-bit longitude)	0.86	>1 B
BitStringMicroBenchmark.getSixBitAsciiString (120-bit name)	44.98	~22 M

NMEAMessageParseBenchmark measures the full cost of constructing a NMEAMessage from a raw sentence string (tag-block detection, field splitting, checksum parsing). AISMessageFactoryBenchmark measures the subsequent AIS payload decode from a pre-parsed NMEAMessage into a typed, immutable AISMessage value object.

Run the benchmark locally with:

./mvnw -Pbench test

Results are written to target/jmh-result.txt.

For more detail, see:

• Immutable value objects in AISmessages v4
• Performance analysis — String to BitString refactor

Application-Specific Messages (ASM)

AISmessages supports decoding of application-specific messages carried in AIS message types 6 and 8.

Supported coverage includes:

• The 24 IMO SN.1/Circ.289 international application-specific message definitions for DAC=001
• Regional support for DAC=200, FI=10 (InlandShipStaticAndVoyageRelatedData)
• A safe fallback to UnknownApplicationSpecificMessage for unsupported combinations

Example:

import dk.tbsalling.aismessages.ais.messages.BinaryBroadcastMessage;
import dk.tbsalling.aismessages.ais.messages.asm.ApplicationSpecificMessage;
import dk.tbsalling.aismessages.ais.messages.asm.WeatherObservation;

BinaryBroadcastMessage binaryMessage = (BinaryBroadcastMessage) aisMessage;
ApplicationSpecificMessage asm = binaryMessage.getApplicationSpecificMessage();

if (asm instanceof WeatherObservation weather) {
    System.out.println("Temperature: " + weather.getAirTemperature());
        System.out.

println("Wind speed: "+weather.getAverageWindSpeed());
}

For the full overview, see AIS Application-Specific Messages.

Receiving AIS over UDP

AISmessages can also listen for AIS data over UDP:

import dk.tbsalling.aismessages.nmea.NMEAMessageHandler;
import dk.tbsalling.aismessages.nmea.NMEAMessageUDPSocket;

public class UDPExample {
    public static void main(String[] args) throws Exception {
        NMEAMessageUDPSocket udpSocket = new NMEAMessageUDPSocket(
                "127.0.0.1",
                10110,
                new NMEAMessageHandler("UDPSRC", aisMessage ->
                        System.out.println("Received: " + aisMessage))
        );

        udpSocket.run();
    }
}

See dk.tbsalling.aismessages.demo.UDPDemoApp for a complete example.

Demos and related projects

The repository includes ready-to-run demo applications:

• dk.tbsalling.aismessages.demo.SimpleDemoApp
• dk.tbsalling.aismessages.demo.SocketDemoApp
• dk.tbsalling.aismessages.demo.UDPDemoApp

You may also want:

• AISutils for higher-level AIS functionality such as tracking and filtering
• AIScli for command-line conversion, filtering, and processing

Documentation

The docs/ directory contains articles and tutorials, including:

• What is AIS?
• Creating a Spring Boot based AIS message decoder
• Creating, sharing, and running a Docker image to decode AIS messages
• Running AISdecoder in a Kubernetes cluster on AWS
• Introducing Java modules in AISmessages

Start here: docs/README.md

Real-world use

AISmessages has been used in production in a wide range of maritime solutions, including traffic monitoring, port operations, tracking, and decision support systems.

Public references and talks include:

• OpenRemote's Safe Waterways project in the Beatrix Canal, NL (video)
• Dakosy's PRISE system for mega-ship sequencing on the Elbe and in the Port of Hamburg (reference)
• Bert Jan Schrijver's "Decode the air around you" talks at DEVOXX BE and DEVOXX UK (YouTube, Parleys)

License

AISmessages is released under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license.

That means it is free for non-commercial use. If you need a commercial license or support, contact Thomas Borg Salling.