Presents your  
XML AND WEB SERVICES E-NEWSLETTER for November 17, 2003 
 
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USE APACHE'S TCP TUNNEL/MONITOR TO DEBUG SOAP   
  
One of the most common tasks during application development is 
debugging. With new tools and new technologies, debugging is essential to 
understanding what's happening and why your application is behaving like
expected. To this end, the Apache Group distributes a nice application
that you can use to monitor and debug your SOAP interfaces. (Note that this 
application only applies to SOAP implementations that use HTTP as the 
transport.)   
  
TCP TUNNEL/MONITOR   
  
The TCP Tunnel/Monitor application is a simple proxy application that 
includes a visual interface. When you run the application, you specify a
host port and a target address and port. TCP Tunnel/Monitor will display
a window with two text areas:   
  
* The text area on the left shows the incoming request, received by the 
application on the host port you specify.   
  
* The text area on the right shows the response received from the target server.   
  
You can use the application to monitor servers locally and remotely. If 
your Web server is local, then you'll specify a host port other than the
one your Web server is currently using. For example, if you're running 
Tomcat on port 8080, then you can start the application with the
following command:   
  
java org.apache.soap.util.net.TcpTunnelGui 8081 localhost 8080   
  
This command runs the TcpTunnelGui class and passes in three 
parameters:

  
* The first parameter specifies the port that the tool will listen on. 
Your SOAP client will have to be redirected to this port rather than 
the normal port in order to see things happen.   
  
* The second parameter is the target address (the local machine in this case).   
  
* The final parameter is the target port (in this case, where Tomcat is listening).   
  
You can point the monitor at remote servers too. Simply change the 
target address and port to match the host you want to monitor. For example, to 
monitor the messages to and from the Google Web service, you can use the
following command:   
  
java org.apache.soap.util.net.TcpTunnelGui 88 api.google.com 80   
  
In this case, your client's SOAP location is now 
http://localhost:88/search/beta2 instead of
http://api.google.com/search/beta2.   
  
SOAP   
  
When you run your SOAP client, it sends a request to the SOAP location 
you've specified. In order to use this tool, the SOAP location will be 
different from normal. Each request is proxied by the monitor program, so 
you have to change the SOAP location of the service you're calling to be
at host localhost and at the port you specified as the host port when 
starting up the tunnel.   
  
For example, if you have an existing Web service client, it may contain 
something like this:   
  
String soaplocation =   
" http://mywebservice.mydomain.com/soap/servlet/rpcrouter";   
URL soapurl = new URL(soaplocation);   
  
You can easily modify this to point to the proxy:   
  
String soaplocation = " http://localhost:88/soap/servlet/rpcrouter";   
URL soapurl = new URL(soaplocation);   
  
In a real application, the URL probably isn't hard-coded in the source 
but in a properties file (or some other externally editable file). In this 
case, it may make sense to have two parameters in your properties 
file--one that points directly to the service and another that points at
the proxy address. Then you could add another property that indicates if 
the service is in "debug" mode and use it to dynamically change where the 
service client points to, like this:   
  
. . .   
String debugmode = myConfiguration.getProperty("debugMode");   
String soaplocation;   
if (debugmode.equalsIgnoreCase("YES")) {   
soaplocation = myConfiguration.getProperty("soapLocation");   
} else {   
soaplocation = myConfiguration.getProperty("soapLocationDebug");   
}   
. . .   
  
HTTP AND OTHER SERVERS   
  
This tool is useful beyond just SOAP messages. It can be used to monitor
any HTTP service as well, and it's not dependent on Apache Web servers. 
Because the tool is a generic proxy, you can use it to monitor HTTP and 
SOAP messages to Microsoft IIS servers, Apache Web servers, Tomcat, 
WebLogic, or any HTTP server.  

Brian Schaffner is an associate director for Fujitsu Consulting. He 
provides architecture, design, and development support for Fujitsu's
Technology Consulting practice.  
  
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