Need more flexibility around conversion strategies and how to bootstrap different conversion strategies. [SPR-6381]

[spring-projects-issues]

Oleg Zhurakousky opened SPR-6381 and commented

Related to #10464

As a developer I need:

• Ability to create ConversionService instance with no default converters pre-registered or only have NumberToString and vice versa type converters:
  For example:
  Object.toString() is not always the right default strategy since implementation of the toString() method often tailored more toward displaying an object in the logs, rather then creating a true String representation of it
  Object to Map and vice versa, also is not always a good default strategy since Object might represent some type of a structure that could be represented as more then a single entry Map
  The bottom line is as a developer I want to have a choice and control as to how canConvert() method behaves. In other words if I want to convert Foo to String and there is no FooToString cnverter I want to see can't convert exception and not rely on the default generic strategy.

Currently in SI we have to remove bunch of converters in order to use the ConversionService

I also need ability to chain/synthesize converters. However, this strategy will not work if we have ObjectTo* and *ToObject converters since everything is an object, which means the default state of such converter must only have strongly typed converters pre-registered or empty.

Overall I think we need flexibility and therefore several strategies needed. So I think what would be appropriate is to have a Factory class with Factory methods fronting the ConversionService creation, this allowing to bootstrap several implementations.

For example

• public static ConversionService createGenericConverter(List additionalConverters) - will retur the instance of GenericConversionService
• public static ConversionService createDefaultConverter(List. additionalConverters) - will retur the instance of DefaultConversionService
• public static ConversionService createSyntheticConverter(List additionalConverters) - will retur the instance of SyntheticConversionService
• public static ConversionService createEmptySyntheticConverter()
  etc. . .

Obviously not passing any additional converters will result in the initial state of the ConversionService to correspond to the implementation of the factory method. Configuration would also be simple:
{CODE}
<bean id="conversionService" class="ConversionServiceFactory" factory-method="createSyntheticConverter">
<constructor-arg>
<list>
. . .

	</list>
</constructor-arg>

</bean>
{CODE}

---

Affects: 3.0 RC2

Issue Links:

• Composing synthetic converters from concrete converters [SPR-5794] #10464 Composing synthetic converters from concrete converters ("depends on")

[spring-projects-issues]

Oleg Zhurakousky commented

Just as another example here is the snippet of the code we currently have in SI:
{CODE}
conversionService = new DefaultConversionService();
conversionService.removeConvertible(Object.class, Map.class);
conversionService.removeConvertible(Map.class, Object.class);
conversionService.removeConvertible(Object.class, String.class);
{CODE}
I would love to only add what I need instead of remove what I don't, simply because I don't know what's there (unless I am familiar with the code) until i try.

[spring-projects-issues]

Keith Donald commented

Added ConversionServiceFactory