Question

I wrote a Java servlet filter on my local machine and deployed it a remote (machine) web server. Unfortunately, it’s been very difficult and time-consuming trying to trace errors reported by Apache Tomcat 5.5, my JSP/servlet engine. I can’t keep writing System.out.println(…), saving, deploying, testing JSP pages, and so on. It’s taking too long. There has to be a better, faster way.

Is it possible to remotely debug servlet filters? I don’t have a web server on my local machine, which is why I’m asking about remote debugging. Specifically, I’m looking for a way to debug, line-by-line, the servlet filter, on-the-fly, as it’s happening on the remote web server. Does such a method exist?

Or, is there a better method than writing to standard output. It’s taking too long and I feel that must be a more efficient means of debugging Java servlet filters.

Note: I’m using Eclipse for development.

Thank you very much for any help.

Update

Thank you all for your help. I really appreciate it.

I added the JVM argument to Tomcat, restarted Tomcat. Then, on the machine with Eclipse, I entered in the appropriate info in the Debug config, put the breakpoint in, and tested. Unfortunately, it did not work. In the config, I left it as Socket Attach, clicked apply, and that was it. I pressed the debug button and it said the connection was refused. I tried ports 8000 and 8001 and both did not work.

Let me explain what I’m trying to do, that might be better.

I have a login page called login.jsp. On that page, is a form whose action attribute is servlet/LoginServlet. When the user submits the form, it calls servlet/LoginServlet, which is mapped to a class in the web.xml file. Let’s call this class com.mysite.mypkg.classA. In class A, it calls a method from another class called com.custom.mypkg.classB. I want to put a breakpoint in classB.

So, using the url with login.jsp page in the Eclipse debugger won’t call it. I tried using servlet/LoginServlet and that also did not work.

What should I put in for the URL? Or, do I debug this type of setup?

Thank you.

Update 2

I found this site here, which is pretty comprehensive. I ran netstat -a and noticed that the debug port is not listed. Windows Firewall is turned off, but there could be another thing blocking the port, who knows. Anyway, I placed the VM argument here and it’s not working.

Thank you.

Answer 1

For remote debugging you need to start the server in debug mode. There are couple of ways doing that.
1 > start the server using

catinlina.bat jpda start

2 > Add an jvm argument to the tomcat java process

-Xdebug -Xrunjdwp:transport=dt_socket,address=8000,server=y,suspend=n

Once the server is started in debug mode , you need to change the perspective of the project in eclipse to debug.
Then go to Run – > Debug configuration.
Double click remote java application and enter the details such as

Remote IP address
Debug port . Default tomcat debug port is 8000. If you use jvm argument, use the port mentioned in the jvm argument.
Click Apply

Go to the java file you want to debug.
Put a break point in the source code and run the scenario you want to test (Eg Web application using browser)

Also , ensure that the code in the java file is in sync with code deployed on remote server.

Happy Debugging!!!

Peace.
Sanket Raut