Snippet

Implementing Custom Type Converters for Spring Data ConversionService

Spring's `ConversionService` provides a unified SPI for executing type conversions between strings and strongly typed domain objects. Implementing `org.springframework.core.convert.converter.Converter<S, T>` allows seamless parsing of raw HTTP request parameters, path variables, and configuration attributes into immutable Java records, keeping web controller action signatures clean and type-safe without manual parsing logic.

snippet.java

java

public record IsoCurrency(String currencyCode, int fractionDigits) {}
 
@Component
public class StringToIsoCurrencyConverter implements Converter<String, IsoCurrency> {
 
    @Override
    public IsoCurrency convert(String source) {
        if (source == null || source.isBlank()) {
            return null;
        }
        String normalized = source.trim().toUpperCase();
        Currency currency = Currency.getInstance(normalized);
        return new IsoCurrency(currency.getCurrencyCode(), currency.getDefaultFractionDigits());
    }
}
 
@Configuration
public class WebFormattingConfiguration implements WebMvcConfigurer {
    @Override
    public void addFormatters(FormatterRegistry registry) {
        registry.addConverter(new StringToIsoCurrencyConverter());
    }
}

spring

Breakdown

public class StringToIsoCurrencyConverter implements Converter<String, IsoCurrency>

Defines a stateless converter contract mapping a source String to a target IsoCurrency record.

Currency currency = Currency.getInstance(normalized);

Validates the string representation and parses standard ISO currency metadata.

registry.addConverter(new StringToIsoCurrencyConverter());

Registers the converter with Spring MVC's FormatterRegistry for automatic parameter binding.

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Implementing Custom Type Converters for Spring Data ConversionService

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