Get content from outputstream

Question

I am using a really old Java version and i am missing a lot of classes. The system runs on an embedded platform. There is a class to execute system commands, but the output from the command is discarded. Is there anyway to cache or get this output another way?

There is another java application that is not coded by us that we interact with. This application starts a test and output the results in the shell. We are not able to edit the source code of that application.

Any suggestions?

Answer 1

You can check ProcessBuilder to run system commands.

       ProcessBuilder pb = new ProcessBuilder("myCommand", "myArg1", "myArg2");
       Map env = pb.environment();
       env.put("VAR1", "myValue");
       env.remove("OTHERVAR");
       env.put("VAR2", env.get("VAR1") + "suffix");
       pb.directory(new File("myDir"));
       File log = new File("log");
       pb.redirectErrorStream(true);
       pb.redirectOutput(Redirect.appendTo(log));
       Process p = pb.start();

Answer 2

Depending on how desperate you are, you can manipulate the standard output of the launched process by adding a "shim" class. Basically, create your own class with a main method which redirects stdout to your desired location (like some known file).

public class HackMain {
  public static void main(String[] args) {
    // ... use reflection to hack System.out ...

    // invoke "real" main
    RealMainClass.main(args);
  }
}

Then add a jar with this class to the invoked process command line and call it instead like java -cp <other_jars>:<hack_jar> HackMain [<args> ...].

Answer 3

If you're using a shell wrapper and you have access to the file system you can try to redirect the output of your command to a file and read it from there:

Ish.execute(fancyCommand + " > myfile.tmp");
InputStream is = null;
    StringBuilder sb = new StringBuilder();
    try {
        is = new BufferedInputStream(new FileInputStream("/path/to/myfile.tmp"));
        int c;
        while ((c = is.read()) != -1){
            sb.append((char)c);
        }
    } catch (IOException ioex) {
        ioex.printStackTrace();
    } finally {
        if (is != null) {
            try {
                is.close();
            } catch (Exception ignore) {
            }
        }
    }

Answer 4

If the external app will run inside the same process, you can try to redirect System.out (using System.setOut()) before the call to the external application.