Question

I’ve been doing some digging with an application system utilizing HttpClient 4.1.x to handle RESTful calls under Spring.

While I’ve got this working great under both directly dealing with the httpclient as well as using as the transport for the RestTemplate, I’ve found that I have a need for something that I’m not sure was covered in execution.

The “BasicResponseHandler” treats the content response as a string and returns it provided that the response from the server is less than 300. The RESTful system I’m working with provides an XML document as part of an error response (status code >= 400). This XML response contains some information that may be of use to the client developer.

What I’d like to see if anyone has any experience dealing with this via the ResponseHandler interface. Essentially, the BasicResponseHandler will toss a ClientProtocolException in the case that there is a status >= 300. The handling AbstractHttpClient implementation will trap that exception, consume the entity silently, then re-throw the IOException (ClientProtocolException) that was thrown.

Would it be advisable to create a sub-class of ClientProtocolException to contain the additional information?

In the case of the error status, unmarshal any existing document into its respective type (if available) and then throw it thus preserving the content of the response.

Or is there another mechanism that I’m missing to handle this case?

Answer 1

The purpose of the ResponseHandler interface is to enable the caller to digest HTTP responses without buffering message content in memory. An extra benefit of using this interface is not having to worry about resource deallocation which is taken care of automatically by HttpClient.

In your particular case you should consider building a higher level domain object from the low level HTTP response content instead of returning a simple, unrepresentative string.

So, instead of throwing an exception, consider returning back to the caller an object consisting of the request status (success, failure, partial response, etc), and a parsed XML document or an JAXB object representing a message content.