CODEWITHSUNDEEP
javaconcurrencyruntime
Caffeinated
Caffeinated

Reputation: 12484

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

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?

Upvotes: 1

Views: 4470

Answers (1)

MadProgrammer
MadProgrammer

Reputation: 347214

  1. 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.
  2. 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)

Upvotes: 3

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