How to use Runtime.getRuntime().exec to run an arbitrary Java program?

Question

I found the following code which uses Runtime.getRuntime().exec to run an arbitrary program (like Notepad.exe ) .

public class RuntimeDemo {

   public static void main(String[] args) {
   try {

   // create a new array of 2 strings
   String[] cmdArray = new String[2];

   // first argument is the program we want to open
   cmdArray[0] = "notepad.exe";

   // second argument is a txt file we want to open with notepad
   cmdArray[1] = "example.txt";

   // print a message
   System.out.println("Executing notepad.exe and opening example.txt");

   // create a process and execute cmdArray and currect environment
   Process process = Runtime.getRuntime().exec(cmdArray,null);

   // print another message
   System.out.println("example.txt should now open.");

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

   }
}

I ran this from Eclipse, and it opens Notepad.exe (or I can use calc.exe also ) .

But what if we want to run an arbitrary Java command from this program, something like :

java -version -

will this run? I see a problem here is that .. where do you see the results of it? If I'm running command-line, it comes out to the command line.. but here?

*"will this run?"* - The question is, have you tried? I would encourage you to use `ProcessBuilder` of `Runtime.exec` it's easy to configure things like the working directory and redirecting the error stream through the process output stream. As you've noted, the example is not consuming the `Process`'s `InputStream`, which allows you to read the output from the `Process`, which would be the next thing you would need to solve — MadProgrammer, Jul 10 '15 at 01:10
For [example](http://stackoverflow.com/questions/19968759/how-to-read-the-std-output-of-another-java-program-in-this-java-program/19969016#19969016) and [example](http://stackoverflow.com/questions/19968759/how-to-read-the-std-output-of-another-java-program-in-this-java-program/19969016#19969016) — MadProgrammer, Jul 10 '15 at 01:10
@MadProgrammer - I tried my hand at it, still not flying though - http://stackoverflow.com/questions/31331717/having-trouble-running-my-program-via-the-getruntime-in-java — Caffeinated, Jul 10 '15 at 02:59
@MadProgrammer - Why do we need ProcessBuilder , and not just Process — Caffeinated, Jul 10 '15 at 03:00
`ProcessBuilder` allows you to change the working directory of that the `Process` is executed in, it allows you to redirect the stdout/err to different locations (like a file or merge them into a single stream for easier processing). I also believe it's executes the command differently from `Runtime#exec`, which has helped solve a number of other problems — MadProgrammer, Jul 10 '15 at 03:07

score 2 · Accepted Answer · answered Jul 10 '15 at 03:12

Use ProcessBuilder of Runtime#exec, it provides a more configurable solution and encourages the use of String[] or List<String> for the commands and parameters, which solves a bunch of issues, especially when your parameters contain spaces.
Read the Process's InputStream

For example...

try {
    String[] command = {"java.exe", "-?"};
    ProcessBuilder pb = new ProcessBuilder(command);
    pb.redirectErrorStream(true);
    Process exec = pb.start();

    BufferedReader br = new BufferedReader(new InputStreamReader(exec.getInputStream()));
    String text = null;
    while ((text = br.readLine()) != null) {
        System.out.println(text);
    }

    System.out.println("Process exited with " + exec.waitFor());
} catch (IOException | InterruptedException exp) {
    exp.printStackTrace();
}

Which outputs

Usage: java [-options] class [args...]
           (to execute a class)
   or  java [-options] -jar jarfile [args...]
           (to execute a jar file)
where options include:
    -d32      use a 32-bit data model if available
    -d64      use a 64-bit data model if available
    -server   to select the "server" VM
                  The default VM is server.

    -cp <class search path of directories and zip/jar files>
    -classpath <class search path of directories and zip/jar files>
                  A ; separated list of directories, JAR archives,
                  and ZIP archives to search for class files.
    -D<name>=<value>
                  set a system property
    -verbose:[class|gc|jni]
                  enable verbose output
    -version      print product version and exit
    -version:<value>
                  require the specified version to run
    -showversion  print product version and continue
    -jre-restrict-search | -no-jre-restrict-search
                  include/exclude user private JREs in the version search
    -? -help      print this help message
    -X            print help on non-standard options
    -ea[:<packagename>...|:<classname>]
    -enableassertions[:<packagename>...|:<classname>]
                  enable assertions with specified granularity
    -da[:<packagename>...|:<classname>]
    -disableassertions[:<packagename>...|:<classname>]
                  disable assertions with specified granularity
    -esa | -enablesystemassertions
                  enable system assertions
    -dsa | -disablesystemassertions
                  disable system assertions
    -agentlib:<libname>[=<options>]
                  load native agent library <libname>, e.g. -agentlib:hprof
                  see also, -agentlib:jdwp=help and -agentlib:hprof=help
    -agentpath:<pathname>[=<options>]
                  load native agent library by full pathname
    -javaagent:<jarpath>[=<options>]
                  load Java programming language agent, see java.lang.instrument
    -splash:<imagepath>
                  show splash screen with specified image
See http://www.oracle.com/technetwork/java/javase/documentation/index.html for more details.
Process exited with 0

This assumes that java.exe is within the PATH environment, otherwise you may be required to provide the full path to it (or change the working directory)

For some reason, Eclipse didn't like this part - `catch (IOException | InterruptedException exp)` — Caffeinated, Jul 10 '15 at 03:32
What is the use of the pipe here? if i just say `public static void main(String[] args) throws InterruptedException` will that suffice ? — Caffeinated, Jul 10 '15 at 03:33
It's simply a "multi" catch block, makes handling multiple exceptions easier by allowing you to group them together. Prior to this, you would need to have a single `catch` for each exception, which was pain if you wanted to handle them in the same way — MadProgrammer, Jul 10 '15 at 03:38
so this is like a Java 1.8 feature I'm guessing . sounds really neat ! — Caffeinated, Jul 10 '15 at 03:48
It’s Java 7 syntax. And when you are using Java 7 or newer, you may simply call [`inheritIO()`](http://docs.oracle.com/javase/7/docs/api/java/lang/ProcessBuilder.html#inheritIO()) on the `ProcessBuilder` to make the subprocess print its output directly to your own console/output, making the entire `readLine`&`println` loop unnecessary. It even allows to enter text on the console if the subprocess requires input… — Holger, Jul 10 '15 at 13:30
@Holger I've had issues with `inheritIO` before, sometimes it makes it easier to read output from python, but other times, it makes it do nothing... — MadProgrammer, Jul 10 '15 at 13:32

How to use Runtime.getRuntime().exec to run an arbitrary Java program?

1 Answers1