Awesome

dotenv

A twelve-factor configuration library for Java 8+.

Features:

seamless integration with Guice (prefer Spring? see here);
zero dependencies;
available in Maven Central.

Usage

<dependency>
    <groupId>com.github.shyiko.dotenv</groupId>
    <artifactId>dotenv</artifactId>
    <version>0.1.1</version>
</dependency>

ENV resolution order (sources higher in the list take precedence over those located lower):

System.getenv()
.env file in current working directory (might not exist)
.env file on the classpath

(java example)

Let's assume you have a jar file (say app.jar) which contains .env file (e.g. printf "SCHEME=http\nHOST=localhost\n# comment\nPORT=8080" > src/main/resources/.env) and Main.java with the following public static void main(...):

Map<String, String> dotEnv = DotEnv.load();
System.out.println(dotEnv.get("SCHEME") + "://" + dotEnv.get("HOST") + ":" + dotEnv.get("PORT"))

Executing the following

printf "HOST=0.0.0.0" > .env
PORT=5050 app.jar

will then output http://0.0.0.0:5050

Integration with Guice

<dependency>
    <groupId>com.github.shyiko.dotenv</groupId>
    <artifactId>dotenv-guice</artifactId>
    <version>0.1.1</version>
</dependency>

(Main.java)

static class S {
    private final String scheme;
    private final String host;
    private final int port;

    @Inject
    public S(
        @DotEnvValue("SCHEME") String scheme, 
        @DotEnvValue("HOST") String host, 
        @DotEnvValue("PORT") int port
    ) {
        this.scheme = scheme;
        this.host = host;
        this.port = port;
    }

    public void run() {
        System.out.println(scheme + "://" + host + ":" + port);
    }
}

public static void main(String[] args) {
    Injector injector = Guice.createInjector(new DotEnvModule()/*, ... */);
    S s = injector.getInstance(S.class);
    s.run();
}

Integration with Spring

(Main.java)

static class S {
    private final String scheme;
    private final String host;
    private final int port;

    @Autowired
    public S(
        @Value("${SCHEME}") String scheme, 
        @Value("${HOST}") String host, 
        @Value("${PORT}") int port
    ) {
        this.scheme = scheme;
        this.host = host;
        this.port = port;
    }

    public void run() {
        System.out.println(scheme + "://" + host + ":" + port);
    }
}

public static void main(String[] args) {
    ConfigurableApplicationContext ctx = new AnnotationConfigApplicationContext();
    ctx.getEnvironment().getPropertySources().addFirst(
        new MapPropertySource("dotenv", new HashMap<>(DotEnv.load()))
    );
    ctx.refresh();
    S s = ctx.getBeanFactory().createBean(S.class);
    s.run();
}

Development

git clone https://github.com/shyiko/dotenv && cd dotenv
./mvnw # shows how to build, test, etc. project

Legal

All code, unless specified otherwise, is licensed under the MIT license.
Copyright (c) 2017 Stanley Shyiko.