使用java和命令提示符写入文件

Question

when I run this command ffmpeg -i "C:\\user\\test.wmv" >C:\\user\\test.wmv_info.txt 2>&1 from command prompt it works but when I try to the same from java file by calling the command prompt it executes all right but does not writes to the file.

Any idea why?

my java code is:

public void getInfoThroughCommandLine(String sourceFilePath) {
    try {

        String infoFile = sourceFilePath+"_info.txt";
        String command = "ffmpeg -i \""
                + sourceFilePath +"\" >"+infoFile+" 2>&1";

        // Execute the command
        Process process = Runtime.getRuntime().exec("cmd.exe /c start " + command);

        logger.info("Executing getInfoThroughCommandLine command: " + command);


                    // Read the response
        BufferedReader input = new BufferedReader(new InputStreamReader(
                p.getInputStream()));
        BufferedReader error = new BufferedReader(new InputStreamReader(
                p.getErrorStream()));

        // Parse the input stream
        String line = input.readLine();
        System.out.println("ffmpeg execution of: " + sourceFilePath);
        while (line != null) {
            System.out.println("\t***" + line);
            line = input.readLine();
        }

        // Parse the error stream
        line = error.readLine();
        System.out.println("Error Stream: " + sourceFilePath);
        while (line != null) {
                        //do somthing
                    }

    } catch (Exception e) {
        System.err.println(e);
    }
}

Answer 1

I assume you're using getRuntime().exec() to execute?

If so the Process object returned by it would be the one giving you access to in/out streams of the command you execute. Just read from it and write your own file.

-- edit based on discussion via comments --

start in "cmd.exe /c start " + command would start the program in a separate window, and I guess the streams of the process are attached to that window.

C:\Users\z000dgqd>start /?
Starts a separate window to run a specified program or command.
........

Try removing it. Ie

    // Change this:
    Process process = Runtime.getRuntime().exec("cmd.exe /c start " + command);
    // to this
    Process process = Runtime.getRuntime().exec("cmd.exe /c " + command);

Answer 2

The > and 2>&1 are shell operators that tells the shell to redirect the output of your command ( ffmpeg -i "C:\\user\\test.wmv" ) to a specific file ( C:\\user\\test.wmv_info.txt ).

Those operators do not work in Java, in Java, you have to explicitly take the standard output and standard error (via Process#getInputStream() and Process#getErrorStream() respectively - I know it seems backwards) and write the output of those streams to file yourself.

Answer 3

Redirection is handled by the command shell -- ie, by CMD.EXE -- and if you're just feeding the line above to Runtime.exec() , it won't be done. You can either arrange to have this command line send to CMD.EXE -- which is complicated to get right -- or you can do the redirection yourself in Java by reading the process output and error streams and storing the data to a file.

Answer 4

Maybe you could write that command out to a .bat file and run that? Not the cleanest solution but it might work.