Just out of curiosity what do you consider a "proper" web service? A web service is simply a URL endpoint that returns data. Whether that data is delimited text, XML, a message using the SOAP protocol, etc. doesn't matter. Just call it wherever you would call it for any web service.
For a web service that takes name/value pairs as input and returns data in the response body commons HttpClient is probably your best bet:
http://commons.apache.org/httpclient/
If you want to pursue using a JMS queue with your HTTP requests ActiveMQ is probably worth a look:
http://activemq.apache.org/
Particularly this page will probably be useful to you:
http://activemq.apache.org/rest.html
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