Capturing stdout when calling Runtime.exec

Question

When experiencing networking problems on client machines, I'd like to be able to run a few command lines and email the results of them to myself.

I've found Runtime.exec will allow me to execute arbitrary commands, but Collecting the results in a String is more interesting.

I realize I could redirect output to a file, and then read from the file, but my spidey sense is telling me there's a more elegant way of doing it.

Suggestions?

Answer 1

Use ProcessBuilder. After calling start() you'll get a Process object from which you can get the stderr and stdout streams.

UPDATE: ProcessBuilder gives you more control; You don't have to use it but I find it easier in the long run. Especially the ability to redirect stderr to stdout which means you only have to suck down one stream.

Answer 2

Runtime.exec() returns a Process object, from which you can extract the output of whatever command you ran.

Answer 3

You need to capture both the std out and std err in the process. You can then write std out to a file/mail or similar.

See this article for more info, and in particular note the StreamGobbler mechanism that captures stdout/err in separate threads. This is essential to prevent blocking and is the source of numerous errors if you don't do it properly!

Answer 4

Have a look at this article.

Answer 5

Using Runtime.exec gives you a process. You can these use getInputStream to get the stdout of this process, and put this input stream into a String, through a StringBuffer for example.

Answer 6

Use Plexus Utils, it is used by Maven to execut all external processes.

Commandline commandLine = new Commandline();
    commandLine.setExecutable(executable.getAbsolutePath());

    Collection<String> args = getArguments();

    for (String arg : args) {
        Arg _arg = commandLine.createArg();
        _arg.setValue(arg);
    }

WriterStreamConsumer systemOut = new WriterStreamConsumer(console);
    WriterStreamConsumer systemErr = new WriterStreamConsumer(console);

returnCode = CommandLineUtils.executeCommandLine(commandLine, systemOut, systemErr, 10);
            if (returnCode != 0) {
   // bad
} else {
  // good
}