Type Conversion

See equivalent in the Servlet stack

Some annotated controller method arguments that represent String-based request input (for example, @RequestParam, @RequestHeader, @PathVariable, @MatrixVariable, and @CookieValue) can require type conversion if the argument is declared as something other than String.

For such cases, type conversion is automatically applied based on the configured converters. By default, simple types (such as int, long, Date, and others) are supported. Type conversion can be customized through a WebDataBinder (see DataBinder) or by registering Formatters with the FormattingConversionService (see Spring Field Formatting).

A practical issue in type conversion is the treatment of an empty String source value. Such a value is treated as missing if it becomes null as a result of type conversion. This can be the case for Long, UUID, and other target types. If you want to allow null to be injected, either use the required flag on the argument annotation, or declare the argument as @Nullable.