4.4 Configuration Properties

You can create type safe configuration by creating classes that are annotated with @ConfigurationProperties.

Micronaut will produce a reflection-free @ConfigurationProperties bean and will also at compile time calculate the property paths to evaluate, greatly improving the speed and efficiency of loading @ConfigurationProperties.

An example of a configuration class can be seen below:

@ConfigurationProperties Example

import io.micronaut.context.annotation.ConfigurationProperties;
import javax.validation.constraints.Min;
import javax.validation.constraints.NotBlank;
@ConfigurationProperties("my.engine") (1)
public class EngineConfig {
    public String getManufacturer() {
        return manufacturer;
    }
    public void setManufacturer(String manufacturer) {
        this.manufacturer = manufacturer;
    }
    public int getCylinders() {
        return cylinders;
    }
    public void setCylinders(int cylinders) {
        this.cylinders = cylinders;
    }
    public CrankShaft getCrankShaft() {
        return crankShaft;
    }
    public void setCrankShaft(CrankShaft crankShaft) {
        this.crankShaft = crankShaft;
    }
    @NotBlank (2)
    private String manufacturer = "Ford"; (3)
    @Min(1L)
    private int cylinders;
    private CrankShaft crankShaft = new CrankShaft();
    @ConfigurationProperties("crank-shaft")
    public static class CrankShaft { (4)
        public Optional<Double> getRodLength() {
            return rodLength;
        }
        public void setRodLength(Optional<Double> rodLength) {
            this.rodLength = rodLength;
        }
        private Optional<Double> rodLength = Optional.empty(); (5)
    }
}

@ConfigurationProperties Example

import io.micronaut.context.annotation.ConfigurationProperties
import javax.validation.constraints.Min
import javax.validation.constraints.NotBlank
@ConfigurationProperties('my.engine') (1)
class EngineConfig {
    @NotBlank (2)
    String manufacturer = "Ford" (3)
    @Min(1L)
    int cylinders
    CrankShaft crankShaft = new CrankShaft()
    @ConfigurationProperties('crank-shaft')
    static class CrankShaft { (4)
        Optional<Double> rodLength = Optional.empty() (5)
    }
}

@ConfigurationProperties Example

import io.micronaut.context.annotation.ConfigurationProperties
import java.util.*
import javax.validation.constraints.Min
import javax.validation.constraints.NotBlank
@ConfigurationProperties("my.engine") (1)
class EngineConfig {
    @NotBlank (2)
    var manufacturer = "Ford" (3)
    @Min(1L)
    var cylinders: Int = 0
    var crankShaft = CrankShaft()
    @ConfigurationProperties("crank-shaft")
    class CrankShaft { (4)
        var rodLength: Optional<Double> = Optional.empty() (5)
    }
}

Once you have prepared a type safe configuration it can simply be injected into your objects like any other bean:

@ConfigurationProperties Dependency Injection

@Singleton
public class EngineImpl implements Engine {
    private final EngineConfig config;
    public EngineImpl(EngineConfig config) {(1)
        this.config = config;
    }
    @Override
    public int getCylinders() {
        return config.getCylinders();
    }
    public String start() {(2)
        return getConfig().getManufacturer() + " Engine Starting V" + getConfig().getCylinders() +
                " [rodLength=" + getConfig().getCrankShaft().getRodLength().orElse(6.0d) + "]";
    }
    public final EngineConfig getConfig() {
        return config;
    }
}

@ConfigurationProperties Dependency Injection

@Singleton
class EngineImpl implements Engine {
    final EngineConfig config
    EngineImpl(EngineConfig config) { (1)
        this.config = config
    }
    @Override
    int getCylinders() {
        config.cylinders
    }
    String start() { (2)
        "${config.manufacturer} Engine Starting V${config.cylinders} [rodLength=${config.crankShaft.rodLength.orElse(6.0d)}]"
    }
}

@ConfigurationProperties Dependency Injection

@Singleton
class EngineImpl(val config: EngineConfig) : Engine {(1)
    override val cylinders: Int
        get() = config.cylinders
    override fun start(): String {(2)
        return "${config.manufacturer} Engine Starting V${config.cylinders} [rodLength=${config.crankShaft.rodLength.orElse(6.0)}]"
    }
}

Configuration values can then be supplied from one of the PropertySource instances. For example:

Supply Configuration

        LinkedHashMap<String, Object> map = new LinkedHashMap(1);
        map.put("my.engine.cylinders", "8");
        ApplicationContext applicationContext = ApplicationContext.run(map, "test");
        Vehicle vehicle = applicationContext.getBean(Vehicle.class);
        System.out.println(vehicle.start());

Supply Configuration

        ApplicationContext applicationContext = ApplicationContext.run(
                ['my.engine.cylinders': '8'],
                "test"
        )
        Vehicle vehicle = applicationContext
                .getBean(Vehicle)
        println(vehicle.start())

Supply Configuration

        val map = mapOf( "my.engine.cylinders" to "8")
        val applicationContext = ApplicationContext.run(map, "test")
        val vehicle = applicationContext.getBean(Vehicle::class.java)
        println(vehicle.start())

The above example prints: "Ford Engine Starting V8 [rodLength=6.0]"

Note for more complex configurations you can structure @ConfigurationProperties beans through inheritance.

For example creating a subclass of EngineConfig with @ConfigurationProperties('bar') will resolve all properties under the path my.engine.bar.