Viper

A generator and a framework for injecting configurations via CDI.

Put all your configuration keys in an enum, and make viper inject the configurations in your beans.

As simple as

Import library and generators in maven:

<dependency>
	<groupId>com.github.civitz.viper</groupId>
	<artifactId>library</artifactId>
	<version>0.1.0-SNAPSHOT</version>
</dependency>
<dependency>
	<groupId>com.github.civitz.viper</groupId>
	<artifactId>generator</artifactId>
	<version>0.1.0-SNAPSHOT</version>
	<scope>provided</scope>
	<optional>true</optional>
</dependency>

Then annotate the enum of your configuration keys as follows:

package tests;

import civitz.viper.CdiConfiguration;

@CdiConfiguration
@PropertyFileResolver(propertiesPath = "/tmp/viper/my.config")
public enum MyConfigs {	
	FIRST_PROPERTY,
	SECOND_PROPERTY;
}

Viper will generate a ConfigurationBean class, which will read properties from the specified path. If properties are missing, the bean will throw an IllegalArgumentException in the initialization method.

Viper will also generate a Configuration qualifier annotation, in this form:

@Qualifier
@Retention(RetentionPolicy.RUNTIME)
@Target({FIELD,TYPE,METHOD,PARAMETER})
public @interface Configuration {
	@Nonbinding
	MyConfigs value() default MyConfigs.FIRST_PROPERTY;
}

Which permits you to inject configuration in this way:

package tests.logic;

import javax.inject.Inject;
import tests.Configuration; // this is generated
import tests.MyConfigs;

public MyApplicationLogic {

	@Inject 
	@Configuration(MyConfigs.FIRST_PROPERTY)	
	String firstProperty;
	
	@Inject
	@Configuration(MyConfigs.SECOND_PROPERTY)
	String secondProperty;

	void myMethod(){
		// use the property, Luke
	}
}

A more complex example

You can tune the generated bean with more annotations:

package tests;
import java.util.function.Predicate;

import javax.enterprise.context.ApplicationScoped;

import com.google.common.primitives.Ints;

import viper.CdiConfiguration;
import viper.PropertyFileResolver;

/*
 * You can specify one or more annotations for the Configuration Bean.
 * In this case, Configuration Bean will have the ApplicationScoped qualifier
 */
@CdiConfiguration.PassAnnotations(ApplicationScoped.class)
/*
 * Tell the processor to create producers also for primitive types: Byte,
 * Character, Short, Integer, Long, Float, Double, Boolean. Take this feature
 * with care: we don't verify if the transformation from string is possible,
 * exceptions may be thrown.
 */
@CdiConfiguration(producersForPrimitives = true)
/*
 * Generate a Properties-based file-sourced configuration resolver with the
 * given configuration file's path
 */
@PropertyFileResolver(propertiesPath = "/tmp/viper/my.config")
public enum CompleteEnum {

	FIRST_PROPERTY("my.particular.key", s -> Ints.tryParse(s) != null),

	/*
	 * You can mark a specific enum constant to be the default key instead of the
	 * first one
	 */
	@CdiConfiguration.DefaultKey
	SECOND_PROPERTY("my.other.key", s -> s.length() >= 10);
	

	String key;
	Predicate<String> validator;

	CompleteEnum(String key) {
		this(key, s -> true);
	}

	CompleteEnum(String key, Predicate<String> validator) {
		this.key = key;
		this.validator = validator;
	}

	/*
	 * You can specify a method to get a validator for a property: if the
	 * property is not valid, the Configuration Bean will throw an
	 * IllegalArgumentException in the initialization method.
	 */
	@CdiConfiguration.ConfigValidator
	public Predicate<String> getValidator() {
		return validator;
	}

	/*
	 * You can specify a method to get a particular string value as a property
	 * key instead of the generic enum constant name in lowercase.
	 */
	@PropertyFileResolver.KeyString
	public String getKeyString() {
		return key;
	}
}

Or you can omit the @PropertyFileResolver and provide your own @Inject-able implementation of ConfigurationResolver<YourEnum> via CDI. For example, you can create a configuration resolver for etcd.

n3wtron/viper

Viper

As simple as

A more complex example