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Type Conversion
Some annotated controller method arguments that represent String
-based request input (such as
@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 (int
, long
, Date
, and others) are supported. You can customize
type conversion 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
.
As of 5.3, non-null arguments will be enforced even after type conversion. If your handler
method intends to accept a null value as well, either declare your argument as Alternatively, you may specifically handle e.g. the resulting |