Java Tutorial/Development/Process

Execute external command and obtain the result

   <source lang="java">

import java.io.BufferedReader; import java.io.InputStreamReader; public class Main {

 public static void main(String[] args) throws Exception{
   Process process = Runtime.getRuntime().exec("ls -al");
   process.waitFor();
   int exitValue = process.exitValue();
   System.out.println("exitValue = " + exitValue);
   BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
   String line = "";
   while ((line = reader.readLine()) != null) {
     System.out.println(line);
   }
 }

}</source>

Helper method to execute shell command

   <source lang="java">

/*

* Copyright (c) 1998-2002 Carnegie Mellon University.  All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in
*    the documentation and/or other materials provided with the
*    distribution.
*
* THIS SOFTWARE IS PROVIDED BY CARNEGIE MELLON UNIVERSITY ``AS IS"" AND
* ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY
* NOR ITS EMPLOYEES BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/

import java.io.*; public abstract class Exec {

   public static Process exec (String[] cmdarray) throws IOException {
       return exec (cmdarray, null, null);
   }
   public static Process exec (String[] cmdarray, String[] envp) throws IOException {
       return exec (cmdarray, envp, null);
   }
   public static Process exec (String[] cmdarray, String[] envp, File directory) throws IOException {
 return 
     isWindows ()
     ? execWindows (cmdarray, envp, directory)
     : execUnix (cmdarray, envp, directory);
   } 
   /*
    * Unix
    */
   static Process execUnix (String[] cmdarray, String[] envp, File directory) throws IOException {
       // instead of calling command directly, we"ll call the shell to change
       // directory and set environment variables.
       // start constructing the sh command line.
       StringBuffer buf = new StringBuffer ();
       if (directory != null) {
           // change to directory
           buf.append ("cd "");
           buf.append (escapeQuote (directory.toString ()));
           buf.append (""; ");
       }
       if (envp != null) {
           // set environment variables.  Quote the value (but not the name).
           for (int i = 0; i < envp.length; ++i) {
               String nameval = envp[i];
               int equals = nameval.indexOf ("=");
               if (equals == -1)
                   throw new IOException ("environment variable "" + nameval 
                                          + "" should have form NAME=VALUE");
               buf.append (nameval.substring (0, equals+1));
               buf.append ("\"");
               buf.append (escapeQuote (nameval.substring (equals+1)));
               buf.append ("\" ");
           }
       }
       
       // now that we have the directory and environment, run "which" 
       // to test if the command name is found somewhere in the path.
       // If "which" fails, throw an IOException.
       String cmdname = escapeQuote (cmdarray[0]); 
       Runtime rt = Runtime.getRuntime ();
       String[] sharray = new String[] { "sh", "-c", buf.toString () + " which \"" + cmdname + "\"" };
       Process which = rt.exec (sharray);
       try {
           which.waitFor ();
       } catch (InterruptedException e) {
           throw new IOException ("interrupted");
       }
       if (which.exitValue () != 0) 
           throw new IOException ("can"t execute " + cmdname + ": bad command or filename"); 
       // finish in 
       buf.append ("exec \"");
       buf.append (cmdname);
       buf.append ("\" ");
       // quote each argument in the command
       for (int i = 1; i < cmdarray.length; ++i) {
           buf.append ("\"");
           buf.append (escapeQuote (cmdarray[i]));
           buf.append ("\" ");
       }
       System.out.println ("executing " + buf);
       sharray[2] = buf.toString ();
       return rt.exec (sharray);
   }
   static String escapeQuote (String s) {
       // replace single quotes with a bit of magic (end-quote, escaped-quote, start-quote) 
       // that works in a single-quoted string in the Unix shell
       if (s.indexOf ("\"") != -1) {
         System.out.println ("replacing single-quotes in " + s);
           s = s.replace(""", ""\\""");
           System.out.println ("to get " + s);
       }
       return s;
   }
   /*
    * Windows
    */
    static boolean isWindows () {
       String os = System.getProperty ("os.name");
 return (os != null && os.startsWith ("Windows"));
    }
    static boolean isJview () {
       String vendor = System.getProperty ("java.vendor");
 return (vendor != null && vendor.startsWith ("Microsoft"));
    }
   static Process execWindows (String[] cmdarray, String[] envp, File directory) throws IOException {
 if (envp != null || directory != null) {
     if (isJview ())
   // jview doesn"t support JNI, so can"t call putenv/chdir
   throw new IOException 
       ("can"t use Exec.exec() under Microsoft JVM");
     
     if (!linked) {
   try {
       System.loadLibrary ("win32exec");
       linked = true;
   } catch (LinkageError e) {
       throw new IOException ("can"t use Exec.exec(): "
            + e.getMessage ());
   }
     }
     
     if (envp != null) {
   for (int i = 0; i < envp.length; ++i)
       putenv (envp[i]);
     }
     
     if (directory != null)
   chdir (directory.toString ());
 }
       return Runtime.getRuntime ().exec (cmdarray);
   }
   static boolean linked = false; // true after System.loadLibrary() is called
   static native boolean putenv (String env);
   static native boolean chdir (String dir);

}</source>

Reading Output from a Command

   <source lang="java">

import java.io.InputStream; public class Main {

 public static void main(String[] argv) throws Exception {
   String command = "ls";
   Process child = Runtime.getRuntime().exec(command);
   InputStream in = child.getInputStream();
   int c;
   while ((c = in.read()) != -1) {
     System.out.println(((char) c));
   }
   in.close();
 }

}</source>

Sending Input to a Command

   <source lang="java">

import java.io.OutputStream; public class Main {

 public static void main(String[] argv) throws Exception {
   String command = "cat";
   Process child = Runtime.getRuntime().exec(command);
   OutputStream out = child.getOutputStream();
   out.write("some text".getBytes());
   out.close();
 }

}</source>