I would like a simple, preferably annotation-based way to inject external properties into a java program, without using the spring framework (org.springframework.beans.factory.annotation.Value;)
SomeClass.java
@Value("${some.property.name}") private String somePropertyName; application.yml
some: property: name: someValue Is there a recommended way to do this in the standard library?
I ended up using apache commons configuration:
pom.xml:
<dependency> <groupId>commons-configuration</groupId> <artifactId>commons-configuration</artifactId> <version>1.6</version> </dependency> src/.../PropertiesLoader.java
PropertiesConfiguration config = new PropertiesConfiguration(); config.load(PROPERTIES_FILENAME); config.getInt("someKey"); /src/main/resources/application.properties
someKey: 2 I did not want to turn my library into a Spring application (I wanted @Value annotations, but no application context + @Component, extra beans, extra Spring ecosystem/baggage which doesn't make sense in my project).
@Value does in Spring, e.g. something like @Inject @Named("some.property.name") private String somePropertyName; (which AFAIK is not actually supported by any of the frameworks that implement JSR-330). Also, the accepted answer is not annotation-based and, moreover, does not even use dependency injection at all. In my mind, this does not answer the question at all.Define application properties here /src/main/resources/application.properties
Define PropertiesLoader class
public class PropertiesLoader { public static Properties loadProperties() throws IOException { Properties configuration = new Properties(); InputStream inputStream = PropertiesLoader.class .getClassLoader() .getResourceAsStream("application.properties"); configuration.load(inputStream); inputStream.close(); return configuration; } } Inject property value in the required class like below,
Properties conf = PropertiesLoader.loadProperties(); String property = conf.getProperty(key); 
I stumbled upon this answer on google, yet i'm not satisfied.
In the end I created Environment class that uses both application properties from @Stone answer and hardcoded env variables. But Im still looking for better options, since I cannot modify ENV_VARIABLE name inside application.propeties, which is what I originally wanted.
public class EnvironmentPlainJava { public int httpsPort() { return Integer.parseInt(PropertiesLoader.loadProperties().getProperty("https.port")); } public String keyStorePath() { return System.getenv("KEY_STORE_PATH"); } } For reference, here is an idiomatic Kotlin version of the @Stone code (using ClassPathResource Spring utility class - doesn't require running Spring!):
fun loadProperties(properties: String = "application.properties"): Properties = ClassPathResource(properties).inputStream.use { inputStream -> Properties().also { it.load(inputStream) } } 
spring-* tags