Immutable @ConfigurationProperties
I have to resolve that problem very often and I use a bit different approach, which allows me to use final
variables in a class.
First of all, I keep all my configuration in a single place (class), say, called ApplicationProperties
. That class has @ConfigurationProperties
annotation with a specific prefix. It is also listed in @EnableConfigurationProperties
annotation against configuration class (or main class).
Then I provide my ApplicationProperties
as a constructor argument and perform assignment to a final
field inside a constructor.
Example:
Main class:
@SpringBootApplication
@EnableConfigurationProperties(ApplicationProperties.class)
public class Application {
public static void main(String... args) throws Exception {
SpringApplication.run(Application.class, args);
}
}
ApplicationProperties
class
@ConfigurationProperties(prefix = "myapp")
public class ApplicationProperties {
private String someProperty;
// ... other properties and getters
public String getSomeProperty() {
return someProperty;
}
}
And a class with final properties
@Service
public class SomeImplementation implements SomeInterface {
private final String someProperty;
@Autowired
public SomeImplementation(ApplicationProperties properties) {
this.someProperty = properties.getSomeProperty();
}
// ... other methods / properties
}
I prefer this approach for many different reasons e.g. if I have to setup more properties in a constructor, my list of constructor arguments is not "huge" as I always have one argument (ApplicationProperties
in my case); if there is a need to add more final
properties, my constructor stays the same (only one argument) - that may reduce number of changes elsewhere etc.
I hope that will help
From Spring Boot 2.2, it is at last possible to define an immutable class decorated with @ConfigurationProperties
.
The documentation shows an example.
You just need to declare a constructor with the fields to bind (instead of the setter way) and to add the @ConstructorBinding
annotation at the class level to indicate that constructor binding should be used.
So your actual code without any setter is now fine :
@ConstructorBinding
@ConfigurationProperties(prefix = "example")
public final class MyProps {
private final String neededProperty;
public MyProps(String neededProperty) {
this.neededProperty = neededProperty;
}
public String getNeededProperty() { .. }
}