从Java运行命令行的问题

Question

I've been trying to run a compiled C program from Java using following commnand. Then I want to get results from process' input stream.

Process p = Runtime.getRuntime().exec(commandLine);

Now, my command is this (first string is path to program, second and third are paths to files, which program takes as params):

trec_eval.8.1\trec_eval.exe trec_eval.8.1\czech TREC\results_2016-04-26_20_52_175.txt

When I run it normally from command line (I'm on Windows 10), it works as expected (C program finishes without errors and prints expected output into the command line), but alas, when I run it from Java, it doesn't work. Both stdout and stderr streams of the process are empty and process' exit status is some error code.

Here is minimal "working" example (I omitted stderr stream, since it made this code snippet too long):

String commandLine = "trec_eval.8.1\\trec_eval.exe" +
            " trec_eval.8.1\\czech + " " + file;
System.out.println("Command: " + commandLine);

Process process = Runtime.getRuntime().exec(commandLine);
BufferedReader stdout = new BufferedReader(new InputStreamReader(process.getInputStream()));

StringBuilder output = new StringBuilder("Output:\n");
for (String line; (line = stdout.readLine()) != null; ) {
        output.append(line).append("\n");
}
System.out.println(output.toString());

int exitStatus = 0;
try {
    exitStatus = process.waitFor();
} catch (InterruptedException ie) {
    ie.printStackTrace();
}
System.out.println("Exit status: " + exitStatus);
stdout.close();

Output from this code are following lines:

Command: trec_eval.8.1\trec_eval.exe trec_eval.8.1\czech TREC\results_2016-04-27_18_27_585.txt
Output:
Exit status: -1073741515

Obviously, I have read several other answers here on Stackoverflow and elsewhere. Unfortunately, code in said answers was pretty much the same as mine (and did not work for me in the same way as my code does not work).

Can someone please tell me, what am I doing wrong? Why is stdout stream empty instead of containing C program's output? Why does not the process exit with status 0 (as it should), but with before-mentioned monstrosity? Finally, if you know, why my Java code does not work as expected, can you explain, why the exact same command works from the the command line?

Thanks in advance.

Answer 1

It seems like the program is not getting something it needs in it's environment. You said the program exited with an error code--so that sounds like your Java code is doing exactly what it should be doing (Starting the program and reading the exit code).

Your paths look relative--perhaps Java isn't starting in the directory you think it is? Try doing a full path to your argument and see if that helps.

Is there a way you can interpret the error code from the app?

If all else fails, try running it through a shell (either cmd /c or sh depending on your OS) using full paths. You can test that without java, then pass the whole thing to java and see if you get the same results.