Receiving XML document and getting attachment via URL

What is the best method to retrieve a file from a provided URL. Here is the scenario. A system will send us an XML document via an HTTP post but the source system is unable to send us the associated attachment as a MIME attachment instead in the XML they will include a extra node with the URL to a file we need to get. What is the ideal method of retrieving this file once we receive the XML message. If the provided link was an ftp site we would hold the message in BPM and use the file adapter but since this is a full url such as http://someserver.com/myfile/file.doc we are looking for the best approach. On thought was a Java Proxy.

Regards