Sunday, May 1, 2016

Konf - Java config system that supports YAML, JSON, Java properties, Java pojos, List, Maps and JavaScript

Konf - Typed Java Config system

Java configuration library similar in concept to TypeSafe config, but uses full YAML or JSON or JavaScript for configuration (and more).
Konf allows you to easily create your own config DSLs.

Using Konf on your project

Konf is in the public maven repo.

Using konf from maven


Using konf from gradle

compile 'io.advantageous.konf:konf:1.3.0.RELEASE'

Using konf from scala sbt

libraryDependencies += "io.advantageous.konf" % "konf" % "1.3.0.RELEASE"

Using konf from clojure leiningen

[io.advantageous.konf/konf "1.3.0.RELEASE"]
Here is an example config for JavaScript.
Konf expects the config variable to be set to a JavaScript object with properties.

JavaScript based configuration for Java

var config = {

  myUri: uri("http://host:9000/path?foo=bar"),

  someKey: {
    nestedKey: 234,
    other: "this text"

You can use full JavaScript for configuration as long as you define a variable called config that results in a JavaScript object which equates to a Java map.

Defining your own DSL

You can define you own config DSL for your environment. We have a full example that shows you how to create a custom config DSL for your internal projects. The example uses Mesosphere and Docker PORT look ups and it is from a real project.

Defining your own config DSL

var config = {

  platform: {

    statsd: "udp://" + getDockerHost() + ":8125",

    servicePort: mesosPortAt(0, 8080),
    adminPort: mesosPortAt(1, 9090),
See the real world for example that uses Konf to find ports under Mesosphere (running in stating or prod) or under Docker (running on a local developers box).


  • implemented in plain Java SDK almost no dependencies (sl4j, and reflekt with no others)
  • supports files in : YAML, JSON, JSON LAX, JavaScript, Java properties or any tree of Map/List basic types and POJOs
  • allows you to easily create your own config DSL
  • merges multiple configs across all formats
  • can load from configs, from classpath, http, file or just an Java Object tree
  • great support for "nesting" (treat any subtree of the config the same as the whole config)
  • users can override the config with Java system properties, java -Dmyapp.foo.bar=10 and sysProp
  • users can override the config with OS environment variables
  • supports configuring an app, with its framework and libraries, all from a single file such as application.yaml
  • parses duration and size settings, "512k" or "10 seconds"
  • converts types, so if you ask for a boolean and the value is the string "yes", or you ask for a float and the value is an int, it will figure it out.
  • API based on immutable Config instances, for thread safety and easy reasoning about config transformations
  • extensive test coverage
This library limits itself to config. If you want to load config from another source, e.g., database or Redis or MongoDB, then you would need to write some custom code. The library has nice support for merging configurations (Configs with fall-backs) so if you build a custom Config from a custom source it's easy to merge it in. Just implement Config and then useconfig(config...) to configure your config into a chain of other configs. This is described at length below see "Loading config files with fallbacks".


The license is Apache 2.0.

Release Notes

Please see Release Notes, and Release Notes In Progress for the latest releases.


The build uses gradle and the tests are written in Java; and, the library itself is plain Java.

Using the Library

import io.advantageous.config.ConfigLoader;

Config conf = ConfigLoader.load("myconfig.js", "reference.js");
int bar1 = conf.getInt("foo.bar");
Config foo = conf.getConfig("foo");
int bar2 = foo.getInt("bar");

Longer Examples

You can see longer examples in tests along with sample config. You can run these examples by git cloning this project and running gradle test.
In brief, as shown in the examples:
You create a Config instance provided by your application. You use ConfigLoader.load() and you can define your own config system. You could setup default reference.yaml or reference.json but you don't have to. You could just load a single level of config. Config is as complex or as simple as you need.
Config can be created with the parser methods in ConfigLoader.load or built up from any POJO object tree or tree of Map/List/Pojos basic value. It is very flexible. Examples are shown below and linked to below that use JSON, YAML and allow you to define your own DSL like config. It is very simple and easy to use.


Objects are immutable, so methods on Config which transform the configuration return a new Config. There is no complex tree of Config objects. Just Config. It is pretty simple to use and understand.

Java interface for Konf is Config.

The Java interface for Konf is Config. You can get a sub Config from Config (getConfig(path)). The path is always in dot notation (this.that.foo.bar). You can also use:
  • hasPath(path)
  • getInt(path)
  • getLong(path)
  • getDouble(path)
  • getBoolean(path) can be true, false, "yes", "no", "on", "off", yes, no, off, on
  • getString(path)
  • getStringList(path) gets a list of strings
  • getConfig(path) gets a sub-config.
  • getMap(path) gets a map which is a sub-config.
  • getConfigList(path) gets a list of configs at the location specified.
  • getIntList(path)
  • getLongList(path)
  • getDoubleList(path)
  • getBooleanList(path)
  • getDuration(path) gets java.time.Duration useful for timeouts
  • getDurationList(path) gets duration list
  • getUri(path) gets java.net.URI useful for connecting to downstream services
  • getUriList(path) useful for connecting to downstream services
The getMap works with JavaScript objects (or Java maps see below for loading config from Java objects, YAML or JSON). The getStringList and getConfigList works with JavaScript array of string and a JavaScript array of JavaScript objects.
Note you get an exception if the path requested is not found. Use hasPath(path) if you think the config path might be missing.
Here is partial glimpse at the Config interface.

Config interface

public interface Config {

    /** Get string at location. */
    String getString(String path);

    /** Checks to see if config has the path specified. */
    boolean hasPath(String path);

    /** Get int at location. */
    int getInt(String path);

    /** Get float at location. */
    float getFloat(String path);

    /** Get double at location. */
    double getDouble(String path);

    /** Get long at location. */
    long getLong(String path);

    /** Get list of strings at location. */
    List<String> getStringList(String path);

    /** Get map at location. */
    Map<String, Object> getMap(String path);

    /** Get a sub-config at location. */
    Config getConfig(String path);

    /** Get list of sub-configs at location. */
    List<Config> getConfigList(String path);

    /**  Get a single POJO out of config at path. */
    <T> T get(String path, Class<T> type);

    /**  Get a list of POJOs. */
    <T> List<T> getList(String path, Class<T> componentType);

    /** Get duration. Good for timeouts */
    Duration getDuration(String path);

    /** Get duration list. */
    List<Duration> getDurationList(String path);

    /** Get int list. */
    List<Integer> getIntegerList(String path);
The getX methods work like you would expect. Given this config file.

JavaScript functions for config

JavaScript functions that we support

  • sysProp(propName) to read a sysProp as in fooSize : sysProp("my.foo.size")
  • sysPropOrDefault(propName, defaultValue) to read a sysProp or a default
  • isWindowsOS()isMacOS()isUnix()isLinux()isSolaris()
  • env() as in fooSize : env('MY_FOO_SIZE') or even fooSize : sysPropOrDefault("my.foo.size", env('MY_FOO_SIZE'))
  • uri() which creates a java.net.URI as in fooURI : uri ("http://localhost:8080/")
  • java.time.Duration is imported as duration
  • java.lang.System is imported as system
  • seconds(units)minutes(units)hours(units)days(units)millis(units) and milliseconds(units) define a Duration which is useful for configuring timeouts and interval jobs
  • constants yesnoonoff for boolean config

Sample config for testing and showing how config works

var config = {

  myUri: uri("http://host:9000/path?foo=bar"),

  someKey: {
    nestedKey: 234,
    other: "this text"

  int1: 1,
  float1: 1.0,
  double1: 1.0,
  long1: 1,
  string1: "rick",
  stringList: ['Foo', 'Bar'],
  configInner: {
    int2: 2,
    float2: 2.0
  uri: uri("http://localhost:8080/foo"),
  myClass: "java.lang.Object",
  myURI: "http://localhost:8080/foo",
  employee: {"id": 123, "name": "Geoff"},
  employees: [
    {id: 123, "name": "Geoff"},
    {id: 456, "name": "Rick"},
    {id: 789, 'name': "Paul"}
We can do the following operations.
First we load the config.

Loading the config.

    private Config config;

    public void setUp() throws Exception {
        config = ConfigLoader.load("test-config.js");
Note that ConfigLoader.load(resources...) takes a variable length string array. By default a resource String can contain a valid URI, which can have the scheme classpathfile, or http. If you do not specify a scheme than the path is assumed to be a classpath resource.

Using different resources

        config = ConfigLoader.load(
Then we show reading basic types with the config object using getX.

Reading basic types from config

    public void testSimple() throws Exception {

        assertEquals(1, config.getInt("int1"));

        assertEquals(asList("Foo", "Bar"), 

        assertEquals("rick", config.getString("string1"));

        assertEquals(1.0, config.getDouble("double1"), 0.001);

        assertEquals(1L, config.getLong("long1"));

        assertEquals(1.0f, config.getFloat("float1"), 0.001);

        //Basic JDK value types are supported like class.
        assertEquals(Object.class, config.get("myClass", Class.class));

        //Basic JDK value types are supported like URI.
                config.get("myURI", URI.class));

                config.get("uri", URI.class));

You can work with nested properties as well.

Reading a nested config from the config

    public void testGetConfig() throws Exception {
        //Read nested config.
        final Config configInner = config.getConfig("configInner");
        assertEquals(2, configInner.getInt("int2"));
        assertEquals(2.0f, configInner.getFloat("float2"), 0.001);

    public void testGetMap() throws Exception {
        //Read nested config as a Java map.
        final Map<String, Object> map = config.getMap("configInner");
        assertEquals(2, (int) map.get("int2"));
        assertEquals(2.0f, (double) map.get("float2"), 0.001);
You can read deeply nested config items as well by specifying the property path using dot notation.

Reading nested properties with dot notation from config

    public void testSimplePath() throws Exception {

        assertEquals(2, config.getInt("configInner.int2"));
        assertEquals(2.0f, config.getFloat("configInner.float2"), 0.001);
You can also read POJOs directly out of the config file.

Reading a pojo directly out of the config file

    public void testReadClass() throws Exception {
        final Employee employee = config.get("employee", Employee.class);
        assertEquals("Geoff", employee.name);
        assertEquals("123", employee.id);
You can read a list of POJOs at once.

Reading a pojo list directly out of the config file

    public void testReadListOfClass() throws Exception {
        final List<Employee> employees = config.getList("employees", Employee.class);
        assertEquals("Geoff", employees.get(0).name);
        assertEquals("123", employees.get(0).id);
You can also read a list of config objects out of the config as well.

Reading a config list directly out of the config file

        final List<Config> employees = config.getConfigList("employees");
        assertEquals("Geoff", employees.get(0).getString("name"));
        assertEquals("123", employees.get(0).getString("id"));

Using Config with YAML

First include a YAML to object parser like YAML Beans or a library like this.

Example YAML

   name: Nathan Sweet
     age: 28
     address: 4011 16th Ave S
     phone numbers:
      - name: Home
        number: 206-555-5138
      - name: Work
        number: 425-555-2306

Using Konf with YAML

//Use YamlReader to load YAML file.
YamlReader reader = new YamlReader(new FileReader("contact.yml"));

//Convert object read from YAML into Konf config
Config config = ConfigLoader.loadFromObject(reader.read());

//Now you have strongly typed access to fields
String address = config.getString("address");
You can also read Pojos from anywhere in the YAML file as well as sub configs.

You can also use Konf with JSON using Boon

See Boon JSON parser project, and Boon in five minutes

Using Konf with JSON

ObjectMapper mapper =  JsonFactory.create();

/* Convert object read from YAML into Konf config.
  'src' can be File, InputStream, Reader, String. */
Config config = ConfigLoader.loadFromObject(mapper.fromJson(src));

//Now you have strongly typed access to fields
String address = config.getString("address");
Boon supports LAX JSON (Json with comments, and you do not need to quote the field).

Working with java.time.Duration

  • getDuration(path) get a duration
  • getDurationList(path) get a duration list
Konf supports "10 seconds" style config for duration as well as having built-in functions and support for ISO-8601. See documentation for duration config for more details.
Konf can reads list of numbers.
  • getIntList reads list of ints
  • getLongList reads list of longs
  • getDoubleList reads list of doubles
  • getFloatList reads list of floats
See documentation list of number configuration for more details.

Konf can read memory sizes

  • getMemorySize(path)
  • getMemorySizeList(path)
This means we support config like:

Sizes supported.

  diskSpace : " 10 gigabytes",
  diskVolumes : [" 10 gigabytes", "10GB", "10 gigabytes", 10]
We support the following size Strings.

Supported size strings

public enum MemorySizeUnit {

    BYTES(1, "B", "b", "byte", "bytes"),
    KILO_BYTES(1_000, "kB", "kilobyte", "kilobytes"),
    MEGA_BYTES(1_000_000, "MB", "megabyte", "megabytes"),
    GIGA_BYTES(1_000_000_000, "GB", "gigabyte", "gigabytes"),
    TERA_BYTES(1_000_000_000, "TB", "terabyte", "terabytes"),
    PETA_BYTES(1_000_000_000_000L, "PB", "petabyte", "petabytes"),
    EXA_BYTES(1_000_000_000_000_000L, "EB", "exabyte", "exabytes"),
    ZETTA_BYTES(1_000_000_000_000_000_000L, "ZB", "zettabyte", "zettabytes");
You can also specify the sizes with built-in functions if you don't want to use strings.

Using built-in functions to create sizes.

  diskVolumes: [kilobytes(10), megabytes(10), bytes(10), gigabytes(10)]

Loading config files with fallbacks

import static io.advantageous.config.ConfigLoader.*;
    private Config config;
        config = configs(config("test-config.js"), config("reference.js"));
You can load config. The config method is an alias for load(resources...). The configs(config...) creates a series of configs where the configs are search from left to right. The first config that has the object (starting from the left or 0 index) will return the object.
Give the following two configs (from the above example).


var config = {
  abc : "abc",


var config = {
  abc : "abcFallback",
  def : "def"
You could run this test.

Testing the reference.js is a fallback for test-config.js.

import static io.advantageous.config.ConfigLoader.*;

        config = configs(config("test-config.js"), config("reference.js"));

        final String value = config.getString("abc");
        assertEquals("abc", value);

        final String value1 = config.getString("def");
        assertEquals("def", value1);
You can load your config anyway you like. The String abc is found when looking up the key abc because it is in the test-config.js which gets read before the value abcFallback which is in reference.js. Yet the def key yields the "def"because it is defined in reference.js but not test-config.js. You can implement the same style config reading and fallback as is in Type Safe Config but with your DSL.


If you like our configuration project, please try our Reactive Java project or our Actor based microservices lib.
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