Override an object with environment values
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README.md

env-override

Utility library to override an object's properties with environment variable values.

Build Status

Available from the jcenter repository as: compile 'com.edgescope:env-override:$version' - see the Releases for the latest version.

Main Purpose

Let you define your application's configuration in a typed configuration, and allow its settings to be overridden by environment variables.

There are a dozen ways to configure your application, and configuration management is often rife with confusion, rot, and bugs.

The approach this tool takes is toward the https://12factor.net/config technique, with the added benefit of using a typed configuration object, which lets you manage your configuration like code.

The main class/method is EnvConfigLoader.overrideFromEnvironment(T config, String environmentPrefix) where config is some object you've created, used for storing your config settings.

Example Usage

See the EnvConfigLoaderSpec and TestAppConfig for more thorough examples, but here's the idea:

Given an object that you used to store your configuration settings, with some local dev/testing defaults:

public class AppConfig {
    String hostName = "test.foo.com";
    String port = 80;
}

Choose a prefix for your environment-specific overrides. e.g.:

export FOO_HOST_NAME="foo.com"

Then wherever you initialize your app's startup configuration, do something like this:

AppConfig appConfig = EnvConfigLoader.overrideFromEnvironment(new AppConfig(), "FOO") 

The AppConfig instance will end up with a hostName of foo.com and port of 80.
i.e. It will have modified the hostName, and left the port with the original value.

RequiresOverride

You can indicate that a configuration field must be overridden using the @RequiresOverride annotation.
This is useful for fields that you know should be overridden in production, and want to an extra check to ensure it happens. For example, using the AppConfig example again:

import com.edgescope.config.RequiresOverride;

public class AppConfig {
    @RequiresOverride
    String hostName = "test.foo.com";
    
    String port = 80;
}

When the EnvConfigLoader.overrideFromEnvironment method is called, it checks that the hostName is overridden.
If not, it will throw a RuntimeException indicating which fields haven't been overridden.

You can disable this validation (e.g. for environments that use all the default values) by setting the envOverride.validationEnabled System property to false. It is enabled by default.

Requirements, Behaviors, Limitations

  • The method will not mutate your original object. It will return a new object with overridden properties.
  • Your property names must strictly match camelCase naming structure.
  • It currently supports a flat set of properties. i.e. It doesn't support nested objects or Lists in configuration.

Dependencies

  • commons-beanutils
  • logback-classic

Issues / Questions

Please open an issue and let me know if you think something's missing, confusing, or broken.