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Spring - Converter Factory

[Last Updated: Oct 17, 2022]

The interface ConverterFactory is used to tie a single converter to an entire class hierarchy type.

Definition of ConverterFactory

(Version: spring-framework 5.3.23)
package org.springframework.core.convert.converter;
   ........
public interface ConverterFactory<S, R> {
    <T extends R> Converter<S, T> getConverter(Class<T> targetType); 1
}
1Get the converter to convert from S to target type T, where T is also an instance of R.

There are number of built-in converter factories provided by Spring. For example let's see StringToNumberConverterFactory:

Source Code of StringToNumberConverterFactory.java

(Version: spring-framework 5.3.23)
package org.springframework.core.convert.support;
   ........
final class StringToNumberConverterFactory<T extends Number> implements ConverterFactory {
    @Override
    public <T extends Number> Converter<String, T> getConverter(Class<T> targetType) {
        return new StringToNumber<>(targetType);
    }
    private static final class StringToNumber implements Converter {
        private final Class<T> targetType;
        public StringToNumber(Class<T> targetType) {
            this.targetType = targetType;
        }
        @Override
        @Nullable
        public T convert(String source) {
            if (source.isEmpty()) {
                return null;
            }
            return NumberUtils.parseNumber(source, this.targetType);
        }
    }
}

Where NumberUtils.parseNumber(String text, Class<T> targetClass) parses the given text into a Number instance of the given target class, using the corresponding decode / valueOf method (if interested check out the source code).


Example

package com.logicbig.example;

import org.springframework.core.convert.ConversionService;
import org.springframework.core.convert.support.DefaultConversionService;

public class ConverterFactoryExample {
  public static void main(String[] args) {
      ConversionService conversionService = new DefaultConversionService();
      //StringToNumberConverterFactory is used
      Double num = conversionService.convert("1.5", Double.class);
      System.out.println(num);
  }
}

Output

1.5

Built-in converter factories

The built-in converter factories are not public, so we cannot find them in API docs. To know what types can be converted by default please use your IDE to view hierarchy of ConverterFactory interface. Following code list all converter factories defined in Spring core:

package com.logicbig.example;

import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider;
import org.springframework.core.convert.converter.ConverterFactory;
import org.springframework.core.type.filter.AssignableTypeFilter;
import java.util.Set;

public class SpringBuiltInConverterFactoriesFinder {
  public static void main(String[] args) {
      ClassPathScanningCandidateComponentProvider provider =
              new ClassPathScanningCandidateComponentProvider(false);
      provider.addIncludeFilter(new AssignableTypeFilter(ConverterFactory.class));
      Set<BeanDefinition> components = provider.findCandidateComponents("org/springframework");
      components.stream()
                .map(BeanDefinition::getBeanClassName)
                .forEach(System.out::println);
  }
}

Output

org.springframework.core.convert.support.StringToEnumConverterFactory
org.springframework.core.convert.support.CharacterToNumberFactory
org.springframework.core.convert.support.StringToNumberConverterFactory
org.springframework.core.convert.support.NumberToNumberConverterFactory
org.springframework.core.convert.support.IntegerToEnumConverterFactory

Example Project

Dependencies and Technologies Used:

  • spring-context 5.3.23 (Spring Context)
     Version Compatibility: 4.0.7.RELEASE - 5.3.23 Version List
    ×

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    Versions in green have been tested.

  • JDK 8
  • Maven 3.8.1

Spring - Converter Factory Example Select All Download
  • spring-converter-factory-example
    • src
      • main
        • java
          • com
            • logicbig
              • example
                • ConverterFactoryExample.java

    See Also