Question

I’m using Eclipse to develop a Java program, and figured I’d add an option to my program to parse stdin if there are no arguments. (otherwise it parses a file)

I am having problems if I execute "somecommand | java -jar myjar.jar" and went to debug… then realized I don’t know how to start a process in Eclipse like that. And if I run it on the command prompt, I can’t attach to a running process since the process starts immediately.

Any suggestions on how to debug?

edit: see, the thing is, I wrote my program originally to take a filename argument. Then I figured it would be useful for it to take stdin as well, so I did abstract InputStream out of my program (as Mr. Queue suggests). It works fine operating on a file (java -jar myjar.jar myfile), but not operating when I run type myfile | java -jar myjar.jar. I suspect that there’s something different in the two scenarios (eof detection is different?) but I really would like to debug.

// overall program structure follows:

public static void doit(InputStream is)
{
    ...
}

public static void main(String[] args)
{
    if (args.length > 0)
    {
        // this leaves out the try-catch-finally block,
        // but you get the idea. 
        FileInputStream fis = new FileInputStream(args[0]);
        doit(fis);
        fis.close();
    }
    else
    {
        doit(System.in);
    }
}

Answer 1

Run your app, with the pipe, on the command line but add JVM args for remote debugging, like this:

-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=1044

suspend=y will tell the JVM to not actually run the program until the debugger is attached.

Next, go into the Eclipse debug launch configurations (Run -> Debug Configurations...) and create a “Remote Java Application” to connect to your app. Run the launch in Eclipse (after setting some breakpoints) and you should be able to debug. Not terribly convenient, but if you can’t reproduce your issues without the pipe, this is an option.