This is the approach to take to do this:
First, you start the HTTP Analyser normally by selecting View Http Analyser within JDeveloper. It then opens in its own window inside JDeveloper, run the HTTP Analyser by clicking > '(the small green button...)'.
Next, you need to tell the RDBMS Web Service client to use this instance of the HTTP Analyser as a proxy, this can be done with the following line:
and here you specify the host where JDeveloper is running as the host, the port is by default 8099, so unless you know that this has been changed, use this.
Now it's time to run the call to the Web Service. The request/response packet pairs will now be listed in the HTTP Analyser. To examine the content of a request/response pair highlight it in the History tab and then click the Data tab.
The should give you further details about the exact request / response sequence taking place.