Trying to call a program within a Java application

Question

Hi,
I am trying to call a program from within a Java application.
Here's my code:
// the program siftwin32 takes it's input via < and outputs using >
String command = "C:/Demo/siftDemoV4/siftDemoV4/siftWin32.exe < c:/demo/query.pgm >c:/demo/query.key";
Process p = Runtime.getRuntime().exec(command);
int val = p.waitFor();
The program "siftwin32" never executes. That is, the .key file is never generated. The value returned from the waitFor() is 1 which I know is bad.
I'm not sure what the problem is. Running siftwin32 from the command line works fine.
Any help would be greatly appreciated!
Thanks,
Neal
Edited by: nealchecka on Nov 28, 2007 10:01 PM

Answer 1

It's probably being executed; you're just passing it bad arguments and confusing it.
The < and > operators are something that the shell uses. They're not arguments to programs typically. When you run it from the command line, it's going through a shell (the command line is the shell, that is to say a program for running other programs).
When you run Runtime.exec, it doesn't go through the shell. The program is executed directly. If you use the version of exec() that takes a single string argument, the string is tokenized on whitespace and the tokens are used as the executable and its arguments.
You have a few options.
One is to write a shell script (or I guess a batch file on windows) that does the i/o redirection, and invoke that script.
Another can be to send all these arguments to the shell by passing them on the command line to the shell, or to "start" or something (I'm not sure about what Windows does specifically). You can find examples online.
Or you can do the redirection yourself, in the Java program. After you exec, use the resulting Process object to get the standard input, standard output, and standard error streams, and write/read/read those streams. If you like you can read from or write to files with those streams. Personally I generally prefer this option, since it has less dependency on the OS, and it's more flexible, and it's more tightly integrated into the Java class.