The best practice to return primitive types from a RESTful service?

From: Liu, Jervis <>
Date: Thu, 29 Nov 2007 04:18:24 -0500

It is mentioned in JSR-311 section 3.1.2 that "An implementation MUST
include pre-packaged EntityProvider implementations for the following
Java and media type combinations: java.lang.String All text media types
(text/*).". However I don't see any places in the spec mentions about
the conversion between a Java primitive types and an entity body. It is
a common use case that I want to map my SQL "select employee _age from
employee where employee _name='john'" to a java method "int
getEmployeeAge(String employeeName)" then expose this as a RESTful
service. Is this the correct way to do REST, or I am still having my
head in a Service-oriented world instead of resource-oriented? Anyway,
let's say my use case is indeed valid, in this case what content type I
shall use to return an int type so that the client can make sense of?

Shall I return int using content type "text/*"? In the case of returning
String, as long as the client knows the returned content type is text,
it should always be able to marshal the response body to a String
without making any further assumptions. However this does not work for
int type. If only information I have on the client side is the content
type "text/*", it would be impossible for me to make sense of the
response, is it a int type, is it a double type? I simply do not know.

Or maybe, return an int using "text/*" is not a good practice in the
RESTful world, using "application/xml" would be better. Can I say
exposing a java method whose signature is " int getEmployeeAge(String
employeeName)" is not a good practice, you should always wrap the result
in a Java object instead, e.g., like " Employee getEmployeeAge(String
employeeName)"? Or maybe, the JSR-311 runtime can go a little bit fancy,
for example, it can generate a wrapper automatically on top of java
primitive types so that the returned result is a valid an xml doc.

Any thoughts would be highly appreciated. And should not JSR-311 spec
include a section to describe how to do the conversion between a Java
primitive types and an entity body?

Jervis Liu

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