The main goal of this project is to explore basic features of com.typesafe:config.

Reference: https://github.com/lightbend/config#overview

com.typesafe:config is a type-safe configuration library for JVM languages.
All we need to do to start using com.typesafe:config is:

• add dependency

<dependency>
    <groupId>com.typesafe</groupId>
    <artifactId>config</artifactId>
    <version>1.3.3</version>
</dependency>

• add application.conf to resources
• get Config class

Config conf = ConfigFactory.load();

• test/resources/application.conf - file with most popular use-cases. It's written in HOCON.
• test/java/ConfigTest - we test if all lines from application.conf file was loaded successfully.
• test/java/Author - util class for mapping specific entry in application.conf directly to the JavaBean.
• test/java/UserStatus - util class for mapping specific entry in application.conf directly to the Enum.

• Assumptions:
  • Config conf = ConfigFactory.load();
  • application.conf has structure:

    predefined {
        ...
    }
    
    conf {
        ...
    }
    

• Basic example

  conf {
      project_name = typesafe-config
  }
  

  conf.getString("conf.project_name") // typesafe-config
  

• Substitutions (way of eliminating copy-paste)

  predefined {
      version : 1.0-SNAPSHOT
  }
  conf {
      project_version : ${predefined.version}
      artifact_version : ${predefined.version}
  }
  

  conf.getString("conf.project_version") // 1.0-SNAPSHOT
  conf.getString("conf.artifact_version") // 1.0-SNAPSHOT
  

  Note:
  Remember if there is no defined yyy then xxx : ${yyy} will cause

  ExceptionInInitializerError: Could not resolve substitution to a value: ${yyy}
  

• Handling JSON objects

  author : {name : michal, surname : tumilowicz}
  

  ConfigObject author = conf.getObject("conf.author");
  Config asConfig = author.toConfig(); // treat it as a Config
  asConfig.getString("name"); // michal
  asConfig.getString("surname"); // tumilowicz
  

• Mapping JSON to JavaBean
  If you have a Java object that follows JavaBean conventions (zero-args constructor, getters and setters), you can automatically initialize it from a Config.

  author : {name : michal, surname : tumilowicz}
  

  Author author = ConfigBeanFactory.create(conf.getObject("conf.author").toConfig(), Author.class);
  author.getName(); // michal
  author.getSurname(); // tumilowicz
  

• Merging
  • Values on the same line are concatenated (for strings and arrays) or merged (for objects).
  • If you duplicate a field with an object value, then the objects are merged with last-one-wins.

  persistence : {specification: JPA, provider : Hibernate, cache : true}
  persistence : {provider : EclipseLink, cache : false, database : Oracle}
  

  is merged to:

  persistence : {specification: JPA, provider : EclipseLink, cache : false, database : Oracle}
  

• Merging + substitution
  Merging is especially useful with substitutions.

  predefined {
      headquarters : {name : "mtumilowicz holding"}
  }
  conf {
      branch_east : ${predefined.headquarters} {branch_name : east}
  }
  

  is merged to:

  headquarters : {name : "mtumilowicz holding", branch_name : east}
  

• Substitutions with default value

  predefined {
  }
  conf {
      web_container : GlassFish
      web_container : ${?predefined.web_container}
  }
  

  Here, the field web_container : ${?predefined.web_container} simply vanishes if there's no value for predefined.web_container. But if you set predefined.web_container - it would be used.

  conf.getString("conf.web_container") // GlassFish
  

  Contrary:

  predefined {
      login: admin
  ]
  conf {
      login : ${?predefined.login}
  }
  

  conf.getString("conf.login") // admin
  

• Lists

  languages : [english, polish, french]
  

  conf.getStringList("conf.languages") // [english, polish, french]
  

• Enums

  user_status : [PENDING, ACTIVE, INACTIVE, DELETED]
  

  public enum UserStatus {
      PENDING, ACTIVE, INACTIVE, DELETED
  }
  

  conf.getEnumList(UserStatus.class, "conf.user_status") // [PENDING, ACTIVE, INACTIVE, DELETED]