Programming language: Java
License: MIT License
Tags: Configuration    

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Properlty - Simple configuration library with placeholders resolution and no magic!

Properlty provides a simple way to configure an application from multiple sources โ€” built in resources, system properties, property files, environment variables, and whatever else you like.

Some features:

  • Recursive placeholders resolution
  • Only 30Kb and no external dependencies
  • Java and Kotlin versions

Getting Started

  1. To get started, add Properlty dependency to your project.

For Kotlin:


For Java:


WARN: use one OR the other. Do not import both the dependencies!

  1. Define some properties. You can use placeholders, for example, in config.properties:
  1. Build a Properlty object that loads properties:


    val properlty = Properlty.builder()
            .add("classpath:config.properties") // loads from the classpath


    final Properlty properlty = Properlty.builder()
            .add("classpath:config.properties")  // loads from the classpath
  1. Look up properties by key:


    val port: Int = properlty.getInt("server.port", 8080); // returns 9090
    val serverUrl = properlty["server.url"] // returns
    val defaultVal = properlty["unknownKey", "defaultValue"] // returns defaultValue


    int port = properlty.getInt("server.port", 8080); // returns 9090

    // the Java API uses Optional for methods that could not produce a valid result.
    // In this case the Optional contains the Strind '' 
    Optional<String> serverUrl = properlty.get("server.url") 
    String defaultVal = properlty.get("unknownKey", "defaultValue") // returns defaultValue

(All examples are in Kotlin from now on; btw, Java code is exactly the same)


In Properlty a "reader" is whatever source of properties. By default, Properlty offers readers to load properties from:

  • Java property files in the file system and in the classpath
  • Java system properties
  • Environment variables
  • Programmatically typed properties

Custom properties readers can be created implementing the com.ufoscout.properlty.reader.Reader interface.

Placeholders resolution

Properlty is able to resolve placeholders recursively. For example:




    val properlty = Properlty.builder()
            .add("./fileOne.properties") // loads from the file system
            .add("./fileTwo.properties") // loads from the file system

    println(properlty["server.url"]) // this prints ''

By default ${ and } delimiters are used. Custom delimiters can be easily defined:

    val properlty = Properlty.builder()
            .delimiters("%(", ")") // using %( and ) as delimiters
            .add( bla bla bla)

Default Values

Placeholders can have default values which are used if the key is not otherwise provided. Example:


# the default value "8080" is used if 'PORT_NUMBER' is not provided

# default is


The default separator for the default value is ":". A custom value can be set through the 'defaultValueSeparator()' method of Properlty.builder().

Case Sensitive settings

By default keys and placeholders are case sensitive. The default behavior can be modified with the caseSensitive() builder method:



    val properlty = Properlty.builder()
            .add("classpath:config.properties") // loads from the classpath
    val serverUrl = properlty["server.url"] // returns

Case insensitive can simplify key overriding through environment variables.

Readers priority -> Last one wins

Properties defined in later readers will override properties defined earlier readers, in case of overlapping keys. Hence, make sure that the most specific readers are the last ones in the given list of locations.

For example:




    val properlty = Properlty.builder()
            .add("classpath:fileOne.properties") // loads from the classpath
            .add("file:./fileTwo.properties") // loads from the file system
            .add(SystemPropertiesReader()) // loads the Java system properties

    // this prints 'urlFromTwo'

BTW, due to the fact that we used SystemPropertiesReader() as last reader, if the "server.url" system property is specified at runtime, it will override the other values.

In addition, it is possible to specify a custom priority:

    val properlty = Properlty.builder()

            // load the properties from the file system and specify their priority
            .add(resourcePath = "file:./fileTwo.properties", priority = Default.HIGHEST_PRIORITY)

            .add("classpath:fileOne.properties") // loads from the classpath
            .add(SystemPropertiesReader()) // loads the Java system properties            

    // this prints 'urlFromTwo'

The default priority is 100. The highest priority is 0. As usual, when more readers have the same priority, the last one wins in case of overlapping keys.

Real life example

A typical real life configuration would look like:

    val properlty = Properlty.builder()

            // case insensitive behavior simplifies matching of environment variables, especially in Linux systems

            // load a resource from the classpath

             // load a file from the file system

            // Add a not mandatory reader, resource not found exceptions are ignored.
            // Here I am adding properties present only during testing.
            .add(resourcePath = "classpath:test.properties", ignoreNotFound = true)

             // load the Environment variables and convert their keys
             // from JAVA_HOME=XXX to JAVA.HOME=XXX
             // This could be desired to override default properties
            .add(EnvironmentVariablesReader().replace("_", "."))

             // Load the Java system properties. They override the Environment variables.

            // build the properlty object 

Properlty API

Properlty has a straightforward API that hopefully does not need detailed documentation.

Some examples:

    val properlty = Properlty.builder()

    // get a String. "defaultValue" is returned if the key is not found
    val aString = properlty["key", "defaultValue"]

    // get an array from the comma separated tokens of the property value
    val anArray = properlty.getArray("key", ",")

    // get an Enum
    val anEnum = properlty.getEnum<NeedSomebodyToLoveEnum>("key")

    // get a Long
    val aLong = properlty.getLong("key")

    // get a Long or default value
    val anotherLong = properlty.getLong("key", 10L)

    // get a BigDecimal
    val aBigDecimal = properlty.getBigDecimal("key")

    // or get a BigDecimal by applying a transformation function to the returned String value
    val anotherBigDecimal = properlty["key", { BigDecimal(it) }]

    // get a list of BigDecimal. The property value is split in tokens using the default list 
    // separator (a comma) then the transformation function is applied to each token
    val aListOfBigDecimals = properlty.getList("key") {BigDecimal(it)}