Custom Converter

It is possible to create a custom Converter type as specified in MicroProfile Config.

A custom Converter requires an implementation of org.eclipse.microprofile.config.spi.Converter. Each implementation requires registration via the ServiceLoader mechanism in the META-INF/services/org.eclipse.microprofile.config.spi.Converter file. Consider:

package org.acme.config;

public class CustomValue {

    private final int number;

    public CustomValue(int number) {
        this.number = number;
    }

    public int getNumber() {
        return number;
    }
}

The corresponding converter can look like:

package org.acme.config;

import org.eclipse.microprofile.config.spi.Converter;

public class CustomValueConverter implements Converter<CustomValue> {

    @Override
    public CustomValue convert(String value) {
        return new CustomValue(Integer.parseInt(value));
    }
}

And registration in:

META-INF/services/org.eclipse.microprofile.config.spi.Converter

org.acme.config.CustomValue

Warning

The custom Converter class must be public, must have a public constructor with no arguments, and must not be abstract.

The CustomValueConverter converts the configuration value to the CustomValue type automatically.

Config config = ConfigProvider.getConfig();
CustomValue value = config.getValue("custom.value", CustomValue.class);

The jakarta.annotation.Priority annotation overrides the Converter priority and change converters precedence to fine tune the execution order. By default, if no @Priority is specified by the Converter, the converter is registered with a priority of 100. Consider:

package org.acme.config;

import jakarta.annotation.Priority;
import org.eclipse.microprofile.config.spi.Converter;

@Priority(150)
public class SecretConverter implements Converter<CustomValue> {

    @Override
    public CustomValue convert(String value) {
        final int secretNumber;
        if (value.startsFrom("OBF:")) {
            secretNumber = Integer.parseInt(SecretDecoder.decode(value));
        } else {
            secretNumber = Integer.parseInt(value);
        }

        return new CustomValue(secretNumber);
    }
}

Two Converters, (CustomValueConverter and SecretConverter) can convert the same type CustomValue. Since SecretConverter has a priority of 150, it will be used instead of a CustomValueConverter which has a default priority of 100 (no annotation).