Settings

A library for loading settings from environment variables.

Using with maven

Add the dependency:

<dependency>
    <groupId>de.fraunhofer.iosb.ilt</groupId>
    <artifactId>Settings</artifactId>
    <version>1.0</version>
</dependency>

Using with gradle

Add the dependency:

compile 'de.fraunhofer.iosb.ilt:Settings:1.0'

Core Usage

Classes that hold names of environment variables implement the interface ConfigDefaults.

Constants that define names of environment variables are annotated with the default value of the variable, and optionally if the variable is a sensitive variable and should not have its value logged.

public class SettingsHolder implements ConfigDefaults {

    @DefaultValue("")
    public static final String NAME_VAR_USERNAME = "username";

    @DefaultValue("")
    @SensitiveValue
    public static final String NAME_VAR_PASSWORD = "password";

    @DefaultValueBoolean(false)
    public static final String NAME_LOG_SENSITIVE_DATA = "logSensitiveData";

    @DefaultValueInt(42)
    public static final String NAME_VAR_PORT = "port";
}

Next, the application can create a Settings or CachedSettings instance and use it to access environment variables:

Settings settings = new CachedSettings();
String username = settings.get(NAME_VAR_USERNAME, SettingsHolder.class);
String password = settings.get(NAME_VAR_PASSWORD, SettingsHolder.class);
int port = settings.getInt(NAME_VAR_PORT, SettingsHolder.class);

The first time any environment variable is requested, its name and the value are logged. When a setting is tagged as @SensitiveValue the value is not logged, unless first explicitly enabled. This can be very useful for debugging and the setting itself can be loaded from an environment variable:

Settings settings = new CachedSettings();
boolean logSensitiveData = settings.getBoolean(NAME_LOG_SENSITIVE_DATA, SettingsHolder.class);
settings.setLogSensitiveData(logSensitiveData);

TODO: Document the use of namespaces and ConfigProvider.