MapFormat

For some use cases it may be desirable to accept a map of arbitrary configuration properties that can be supplied to a bean, especially if the bean represents a third-party API where not all the possible configuration properties are known. For example, a datasource may accept a map of configuration properties specific to a particular database driver, allowing the user to specify any desired options in the map without coding each property explicitly.

For this purpose, the MapFormat annotation lets you bind a map to a single configuration property, and specify whether to accept a flat map of keys to values, or a nested map (where the values may be additional maps).

@MapFormat Example

import io.micronaut.context.annotation.ConfigurationProperties;
import io.micronaut.core.convert.format.MapFormat;
import javax.validation.constraints.Min;
import java.util.Map;
@ConfigurationProperties("my.engine")
public class EngineConfig {
    @Min(1L)
    private int cylinders;
    @MapFormat(transformation = MapFormat.MapTransformation.FLAT) (1)
    private Map<Integer, String> sensors;
    public int getCylinders() {
        return cylinders;
    }
    public void setCylinders(int cylinders) {
        this.cylinders = cylinders;
    }
    public Map<Integer, String> getSensors() {
        return sensors;
    }
    public void setSensors(Map<Integer, String> sensors) {
        this.sensors = sensors;
    }
}

@MapFormat Example

import io.micronaut.context.annotation.ConfigurationProperties
import io.micronaut.core.convert.format.MapFormat
import javax.validation.constraints.Min
@ConfigurationProperties('my.engine')
class EngineConfig {
    @Min(1L)
    int cylinders
    @MapFormat(transformation = MapFormat.MapTransformation.FLAT) (1)
    Map<Integer, String> sensors
}

@MapFormat Example

import io.micronaut.context.annotation.ConfigurationProperties
import io.micronaut.core.convert.format.MapFormat
import javax.validation.constraints.Min
@ConfigurationProperties("my.engine")
class EngineConfig {
    @Min(1L)
    var cylinders: Int = 0
    @MapFormat(transformation = MapFormat.MapTransformation.FLAT) (1)
    var sensors: Map<Int, String>? = null
}

EngineImpl

@Singleton
public class EngineImpl implements Engine {
    @Inject
    EngineConfig config;
    @Override
    public Map getSensors() {
        return config.getSensors();
    }
    @Override
    public String start() {
        return "Engine Starting V" + getConfig().getCylinders() +
               " [sensors=" + getSensors().size() + "]";
    }
    public EngineConfig getConfig() {
        return config;
    }
    public void setConfig(EngineConfig config) {
        this.config = config;
    }
}

EngineImpl

@Singleton
class EngineImpl implements Engine {
    @Inject EngineConfig config
    @Override
    Map getSensors() {
        config.sensors
    }
    @Override
    String start() {
        "Engine Starting V$config.cylinders [sensors=${sensors.size()}]"
    }
}

EngineImpl

@Singleton
class EngineImpl : Engine {
    override val sensors: Map<*, *>?
        get() = config!!.sensors
    @Inject
    var config: EngineConfig? = null
    override fun start(): String {
        return "Engine Starting V${config!!.cylinders} [sensors=${sensors!!.size}]"
    }
}

Now a map of properties can be supplied to the my.engine.sensors configuration property.

Use Map Configuration

        Map<String, Object> map = new LinkedHashMap<>(2);
        map.put("my.engine.cylinders", "8");
        Map<Integer, String> map1 = new LinkedHashMap<>(2);
        map1.put(0, "thermostat");
        map1.put(1, "fuel pressure");
        map.put("my.engine.sensors", map1);
        ApplicationContext applicationContext = ApplicationContext.run(map, "test");
        Vehicle vehicle = applicationContext.getBean(Vehicle.class);
        System.out.println(vehicle.start());

Use Map Configuration

        ApplicationContext applicationContext = ApplicationContext.run(
                ['my.engine.cylinders': '8',
                 'my.engine.sensors'  : [0: 'thermostat',
                                         1: 'fuel pressure']],
                "test"
        )
        def vehicle = applicationContext.getBean(Vehicle)
        println(vehicle.start())

Use Map Configuration

        val subMap = mapOf(
            0 to "thermostat",
            1 to "fuel pressure"
        )
        val map = mapOf(
            "my.engine.cylinders" to "8",
            "my.engine.sensors" to subMap
        )
        val applicationContext = ApplicationContext.run(map, "test")
        val vehicle = applicationContext.getBean(Vehicle::class.java)
        println(vehicle.start())

The above example prints: "Engine Starting V8 [sensors=2]"