Tutorials : Web Services with Axis :

The tcpmon Utility

The idea behind a utility like tcpmon is that you place it between the client and the server, and let it listen to the traffic. Without tcpmon the flow is like this (using the NHLService example from above), where the server listens to port 8080:

tcpmon listens for traffic to a specific port and simply redirects it to another port number. So now we change our client to talk to port 8081 for example, and let tcpmon listen to this. When it catches some traffic it'll show it in a window and sends it on to another port of our choice, in this example we'll choose port 8080, where we have the Tomcat server running.

To start tcpmon enter this command from the lib-directory (where the axis.jar file is):

>java -cp axis.jar org.apache.axis.utils.tcpmon 8081 localhost 8080

This will bring up a GUI like this (click to enlarge):

We now change the NHLServiceClient code to connect to port 8081 in stead of 8080 and then run it again. In the upper part of the tcpmon window we can now see the SOAP data (and the HTTP headers) sent from NHLServiceClient. Immediately after the SOAP reply from the server appears in the lower window (click on image to enlarge):

The SOAP message from the client is this:

<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope 
   SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" 
   xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
   xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/">
   <SOAP-ENV:Body>
     <getCurrentPosition>
        <arg0 xsi:type="xsd:string">central</arg0>
        <arg1 xsi:type="xsd:string">detroit</arg1>
     </getCurrentPosition>
   </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

I have reformatted the message to ease reading. The body of the SOAP-message contains the name of the service-method (in bold) and the two string parameters (also in bold). The types of the two arguments (strings) are given as XML schema type declarations (xsi:type="xsd:string").

The answer from the server is this:

<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope  
   xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <SOAP-ENV:Body>
      <getCurrentPositionResponse 
        SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
         <getCurrentPositionResult xsi:type="xsd:string">1</getCurrentPositionResult>
      </getCurrentPositionResponse>
 </SOAP-ENV:Body>
</SOAP-ENV:Envelope> 

The result "1" is wrapped thoroughly in the answer returned. Note again, that the returned message explicitly states the type of the result.

The tcpmon utility is a general utility that can be used to inspect tcp-traffic. You may try to use your browser as the client and enter this URL:

http://localhost:8081/axis/something.jws

and then watch the HTTP-commands and the HTML returned.

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