在cmd上运行的命令但在Java代码中不起作用

Question

I am using mkvmerge to merge an avi file and ass file into an mkv file. My current directory where I have the executable file and java file is in a folder called auto-mkvmerge . When I use the following in command-line it works normally, mkvmerge.exe -o ../auto-done/098.mkv ../auto-vid/098.avi ../auto-sub/098.ass I get the output correct. When I run my java code, it does not work, and gives me an error.

My java code. Main.java

import java.io.*;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        File vidDir = new File(args[0]);
        File subDir = new File(args[1]);
        File outDir = new File(args[2]);

        String[] vids = vidDir.list();
        String[] subs = subDir.list();

        for(int i = 0; i < vids.length; i++) {
            int r = mergeAviAndAss(vids[i], subs[i], args[2]);
        }
    }

    private static int mergeAviAndAss(String aviFileName, String assFileName, String doneDir) {
        try {
            ProcessBuilder pb = new ProcessBuilder("mkvmerge.exe", "-o", doneDir + "/" + aviFileName.substring(0, aviFileName.length() - 4) + ".mkv", "\"" + aviFileName + "\"", "\"" + assFileName + "\"");
            Process p = pb.start();

            InputStream inputStream = p.getInputStream();
            BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));

            String line;
            while((line = br.readLine()) != null)
                System.out.println(line);

            return p.waitFor();
        } catch(IOException e) {
            e.printStackTrace();
        } catch(InterruptedException e) {
            e.printStackTrace();
        }

        return -1;
    }
}

And when I execute it using the following line (after compiling my java code): java Main ../auto-vid ../auto-sub ../auto-done > log.txt

mkvmerge v6.6.0 ('The Edge Of The In Between') built on Dec  1 2013 17:55:00

Error: The file '098.avi' could not be opened for reading: open file error.

mkvmerge v6.6.0 ('The Edge Of The In Between') built on Dec  1 2013 17:55:00

Error: The file '099.avi' could not be opened for reading: open file error.

mkvmerge v6.6.0 ('The Edge Of The In Between') built on Dec  1 2013 17:55:00

Error: The file '100.avi' could not be opened for reading: open file error.

mkvmerge v6.6.0 ('The Edge Of The In Between') built on Dec  1 2013 17:55:00

Error: The file '101.avi' could not be opened for reading: open file error.

mkvmerge v6.6.0 ('The Edge Of The In Between') built on Dec  1 2013 17:55:00

Error: The file '102.avi' could not be opened for reading: open file error.

mkvmerge v6.6.0 ('The Edge Of The In Between') built on Dec  1 2013 17:55:00

Error: The file '103.avi' could not be opened for reading: open file error.

Is there something wrong with my code, or the way I've written it, because if it works normally when I type it in command-line it should be working in my java code.

Answer 1

I think you can use Runtime.exec(java.lang.String[]) and use Runtime.getRuntime().exec("cmd \\c here goes your command") on Windows to launch its console with a specified command.

EDIT: to just run the needed command, use Runtime.getRuntime().exec("here goes your command")

Answer 2

It's a path problem. You can:

• Run your java program passing the absolute paths of the video files: java Main c:\\pathtovideo1\\video1.mvk c:\\pathtovideo2.avi ...
• Go to the path where all the videos are, and execute java c:\\pathtomain\\Main video1.mvk video2.avi ...
• Finally, you can especify more complex code in the java to deal with paths (attach a fixed path for the videos, etc.)

If this options work, you can figure out that there will also be a relative path that will work, probabilly java Main ../auto-done/098.mkv ../auto-done/098.avi ...

Answer 3

This is a problem with paths as pointed out by techurbana.

You need to set the working directory on your process by invoking the .directory(String) method of the process builder before starting the process. You need to give it the root directory of the application.

You can get the current working directory of the JAVA executable (may or may not be where you store your mkvmerg.exe) by doing a:

 File dir = new File("");
 dir.getAbsolutePath();

If your mkvmerg.exe utility has a class path entry in your system (on windows anyway) you should be able to run mkvmerg.exe from any directory.

Then if you have the files you wish mkvmerge to work on in some sub folder say FolderA you do:

 File subDir = new File(dir, "FolderA");
 subDir.getAbsolutePath();

Just try printing out all the paths you are using to console during runtime to verify that the paths to the files, and to the executables are correct, and debugging should be a snap.

Please review the example of managing paths below. It just opens up files in the current directory with notepad, but is pretty much exactly what you want to do. To run this, pass some path as an argument to main().

EDIT - I just realized that I never actually make use of the path passed into the application, and only ever look for the first file in the current directory of the java executable, but you get the point.

 import java.io.BufferedReader;
 import java.io.File;
 import java.io.InputStream;
 import java.io.InputStreamReader;

 public class MainTest {

public static void main(String[] args) {
    // passes in a directory

    if (args.length > 0) {
        doSomethingWithCMD(args[0]);
    }
}

public static void doSomethingWithCMD(String filesDir) {


    try {
        File currDir = new File("");
        // this is a bit weird, but listFiles didnt return anything without
        // this next line.
        currDir = new File(currDir.getAbsolutePath());
        System.out.println(currDir.getAbsolutePath());

        // build our command with a string builder
        StringBuilder sb = new StringBuilder();

        // get the list of files
        File[] files = currDir.listFiles();

        // if there are no files this will be null so check first
        if (!(files == null)) {
            for (File f : files) {
                if (f.isFile()) {
                    sb.append("notepad ");
                    sb.append("\"" + f.getAbsolutePath());
                    sb.append("\"");
                    break;
                }
            }
        }
                    // create our process builder
        // first with no working dir & absolute paths
        ProcessBuilder pb = new ProcessBuilder(sb.toString());
        Process p = pb.start();

        InputStream inputStream = p.getInputStream();
        BufferedReader br = new BufferedReader(new InputStreamReader(
                inputStream));

        String line;
        while ((line = br.readLine()) != null) {
            System.out.println(line);
        }
        // cleanup
        try {
            inputStream.close();
        }
        catch (Exception ignore) {

        }
        try {
            br.close();
        }
        catch (Exception ignore) {

        }

        sb = new StringBuilder();
        // now we rebuild our command using relative paths instead of
        // absolute ones
        if (!(files == null)) {
            for (File f : files) {
                if (f.isFile()) {
                    sb.append("notepad ");
                    sb.append("\"" + f.getName());
                    sb.append("\"");
                    break;
                }
            }
        }

        pb = new ProcessBuilder(sb.toString());
                    //set the working directory
        pb.directory(currDir);
        p = pb.start();

        inputStream = p.getInputStream();
        br = new BufferedReader(new InputStreamReader(inputStream));

        line = null;
        while ((line = br.readLine()) != null) {
            System.out.println(line);
        }

    }
    catch (Exception e) {
        e.printStackTrace();
    }
}
 }