Java Servlet to handle post messages, responses and errors

We have a servlet written in java which create http post requests, we need something to manages server responses. More info: 1. About five requests 2. About 20 erros types Scenario: We have three actors: Client - Servlet - External service The servlet is the one we are going to work on. 1. An external client calls via http the servlet specifying in parameters the kind of request to do and its data. 2. The servlet builds the corresponding new http post message, attaches digital signature and send it to an external service 3. The servlet waits for a response from the external service 4. In case of positive response, parse response content and send xml data to client 5. In case of error the servlet writes text logs, manages eventul retries and send xml data to client