How to pre-process values from spring configuration file?

Question

I have a configuration parameter "myconfig.defaultSize" whose value is defined, for example, as "10MB", in the application.properties file.

In the other hand, I have a @Component class with @ConfigurationProperties annotation mapping those configuration parameter, as follows.

@Component
@ConfigurationProperties(prefix="myconfig")
public class StorageServiceProperties {
   private Long defaultSize;
   //...getters and setters
}

So, how can I would apply a method to convert the String value into Long?

Answer 1

You can't have such generic converter applied on a property-to-property basis. You could register a converter from String to Long but it would be called for every such case (any property of type Long basically).

The purpose of @ConfigurationProperties is to map the Environment to a higher-level data structure. Perhaps you could do that there?

@ConfigurationProperties(prefix="myconfig")
public class StorageServiceProperties {
    private String defaultSize;
    // getters and setters

    public Long determineDefaultSizeInBytes() {
        // parsing logic
    }

}

If you look at the multipart support in Spring Boot, we keep the String value and we use the @ConfigurationProperties object to create a MultipartConfigElement that is responsible of the parsing. That way you can specify those special values in code and configuration.