Sometimes, application servers don’t display the line numbers during printing the trace but instead just print the method name with the “(Unknown Source)” on it.

eg. something like this.

Exception in thread “main” java.lang.ArithmeticException at TraceWithoutLineNumbers.main(Unknown Source)

I wrote this small class to just help me learn why the line numbers get missed and Unknown Source comes up when the trace gets printed.

public class TraceWithoutLineNumbers {

public static void main(String[] args) {

System.out.println(“hello world”);

if (true){ throw new ArithmeticException(); } System.out.println(“very true”);

}

}

For the above code, I gave a

javac TraceWithoutLineNumbers.java

and got

java TraceWithoutLineNumbers hello world Exception in thread “main” java.lang.ArithmeticException at TraceWithoutLineNumbers.main(TraceWithoutLineNumbers.java:9)

Cool. Got the line number.

By default, the minimal debugging option is on. (Only line number and source file information is generated). Here is the list of all the other java compiler options.

So, I do a

javac -g:none TraceWithoutLineNumbers.java

java TraceWithoutLineNumbers hello world Exception in thread “main” java.lang.ArithmeticException at TraceWithoutLineNumbers.main(Unknown Source)

There is nothing you could do on this if the class is built and run by the server ( read if you dont have control over the class’ compilation). However, if it is a standalone class, you can very well do a javac -g .

Or use this option.

-g:{keyword list}

Generate only some kinds of debugging information, specified by a comma

separated list of keywords. Valid keywords are:

source

 Source file debugging information

lines

 Line number debugging information

vars

 Local variable debugging information

Probably, the app server or the web server you are running your class on would have disabled the debugging option for performance purposes.

http://java.sun.com/j2se/1.5.0/docs/tooldocs/windows/javac.html#options