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A lightweight and extensible library to resolve application properties from various external sources.

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Externalized Properties

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A lightweight and extensible library to resolve application properties from various external sources.

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Externalized Properties was inspired by the The Twelve Factor Methodology's section III. Config.

The goal of this library is to make it easy for applications to implement configuration best practices by providing easy-to-use APIs as well as providing the flexibility to choose where to store their configurations/properties.

🛠️ Installation

Gradle

implementation "io.github.joel-jeremy.externalized-properties:externalized-properties-core:${version}"
// Optional/additional resolvers
implementation "io.github.joel-jeremy.externalized-properties:externalized-properties-database:${version}"
implementation "io.github.joel-jeremy.externalized-properties:externalized-properties-git:${version}"

Maven

<dependency>
  <groupId>io.github.joel-jeremy.externalized-properties</groupId>
  <artifactId>externalized-properties-core</artifactId>
  <version>${version}</version>
</dependency>
<!-- Optional/additional resolvers -->
<dependency>
  <groupId>io.github.joel-jeremy.externalized-properties</groupId>
  <artifactId>externalized-properties-database</artifactId>
  <version>${version}</version>
</dependency>
<dependency>
  <groupId>io.github.joel-jeremy.externalized-properties</groupId>
  <artifactId>externalized-properties-git</artifactId>
  <version>${version}</version>
</dependency>

🧩 Java 9 Module Names

Externalized Properties jars are published with Automatic-Module-Name manifest attribute:

  • Core - io.github.joeljeremy.externalizedproperties.core
  • Database Resolver - io.github.joeljeremy.externalizedproperties.database
  • Git Resolver - io.github.joeljeremy.externalizedproperties.git

Module authors can use above module names in their module-info.java:

module foo.bar {
  requires io.github.joeljeremy.externalizedproperties.core;
  requires io.github.joeljeremy.externalizedproperties.database;
  requires io.github.joeljeremy.externalizedproperties.git;
}

🌟 Features

Externalized Properties takes full advantage of Java's Dynamic Proxies (Why Dynamic Proxies?).

✔️ Property Resolution

✔️ Conversion

✔️ Variable Expansion

✔️ Processing

✔️ Profiles

✔️ Ordinal Components

🏎️ Quick Start

Properties are mapped to proxy interface methods by using the @ExternalizedProperty annotation.

(For more advanced scenarios, please see the feature documentations.)

Given an interface:

public interface ApplicationProperties {
  @ExternalizedProperty("java.home")
  String javaHome();

  @ExternalizedProperty("encrypted.property")
  @Decrypt("MyDecryptor")
  String encryptedProperty();

  @ExternalizedProperty("java.version")
  int javaVersion();
}

We can initialize and start resolving external configurations/properties by:

public static void main(String[] args) {
  // 1. Configure and build the ExternalizedProperties instance.
  ExternalizedProperties externalizedProperties = buildExternalizedProperties();

  // 2. Initialize a proxy using the ExternalizedProperties.
  ApplicationProperties props = externalizedProperties.initialize(ApplicationProperties.class);

  // 3. Resolve the properties.
  String javaHome = props.javaHome();
  String encryptedProperty = props.encryptedProperty();
  int javaVersion = props.javaVersion();
}

private static ExternalizedProperties buildExternalizedProperties() {
  return ExternalizedProperties.builder()
      .defaults() 
      .resolvers(...)
      .processors(...)
      .converters(...) 
      .build();
}

🧪 Samples

More sample can be found here: https://github.com/joel-jeremy/externalized-properties-samples