Java/Development Class/Runtime

Calculate process elapsed time

   <source lang="java">

public class Main {

 public static void main(String[] args) {
   long start = System.nanoTime();
   System.out.println("Start: " + start);
   for (int i = 0; i < 100; i++) {
     for (int j = 0; j < 100; j++) {
       System.out.println("asdf");
     }
   }
   long end = System.nanoTime();
   System.out.println("End  : " + end);
   long elapsedTime = end - start;
   System.out.println(elapsedTime + " nano seconds");
 }

}

 </source>
   
  
 
  

Command and its arguments supplied in an array

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   String[] commands = new String[] { "grep", "hello world", "/tmp/f.txt" };
   commands = new String[] { "grep", "hello world", "c:\\f.txt" };
   Process child = Runtime.getRuntime().exec(commands);
 }

}

 </source>
   
  
 
  

Determine when the application is about to exit

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   Runtime.getRuntime().addShutdownHook(new Thread() {
     public void run() {
       System.out.println("Do shutdown work ...");
     }
   });
 }

}

 </source>
   
  
 
  

Execute a command from code

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   // Execute a command without arguments
   String command = "ls";
   Process child = Runtime.getRuntime().exec(command);
   // Execute a command with an argument
   command = "ls /tmp";
   child = Runtime.getRuntime().exec(command);
 }

}

 </source>
   
  
 
  

Execute a command with an argument that contains a space

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   String[] commands = new String[] { "grep", "hello world", "/tmp/f.txt" };
   commands = new String[] { "grep", "hello world", "c:\\f.txt" };
   Process child = Runtime.getRuntime().exec(commands);
 }

}

 </source>
   
  
 
  

Execute a command with an argument that contains a space: use array

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {

   String[] commands = new String[] { "grep", "hello world", "/tmp/f.txt" };
   commands = new String[] { "grep", "hello world", "c:/f.txt" };
   Process child = Runtime.getRuntime().exec(commands);
 }

}

 </source>
   
  
 
  

Execute a command with more than one argument

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   // Execute a command with an argument that contains a space
   String[] commands = new String[] { "grep", "hello world", "/tmp/f.txt" };
   commands = new String[] { "grep", "hello world", "c:\\f.txt" };
   Process child = Runtime.getRuntime().exec(commands);
 }

}

 </source>
   
  
 
  

Execute system command

   <source lang="java">

import java.io.IOException; public class Main {

 public static void main(String[] args) throws IOException {
   String cmd = "cmd.exe /c start ";
   // String file = "c:\\version.txt";
   // String file = "http://www.google.ru";
   // String file = "c:\\";
   // String file = "mailto:author@my.ru";
   String file = "mailto:";
   Runtime.getRuntime().exec(cmd + file);
 }

}

 </source>
   
  
 
  

From Runtime.exec() to ProcessBuilder

   <source lang="java">

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.util.Arrays; public class Main {

 public static void main(String args[]) throws IOException {
   Runtime runtime = Runtime.getRuntime();
   Process process = runtime.exec(args);
   InputStream is = process.getInputStream();
   InputStreamReader isr = new InputStreamReader(is);
   BufferedReader br = new BufferedReader(isr);
   String line;
   System.out.printf("Output of running %s is:", Arrays.toString(args));
   while ((line = br.readLine()) != null) {
     System.out.println(line);
   }
 }

}

 </source>
   
  
 
  

Get amount of free memory within the heap in bytes.

   <source lang="java">

public class Main {

 public static void main(String[] argv) {
   long heapFreeSize = Runtime.getRuntime().freeMemory();
   System.out.println(heapFreeSize);
 }

}

 </source>
   
  
 
  

Get current size of heap in bytes

   <source lang="java">

public class Main {

 public static void main(String[] argv) {
   long heapSize = Runtime.getRuntime().totalMemory();
   System.out.println(heapSize);
 }

}

 </source>
   
  
 
  

Get maximum size of heap in bytes.

   <source lang="java">

public class Main {

 public static void main(String[] argv) {
   long heapMaxSize = Runtime.getRuntime().maxMemory();
   System.out.println(heapMaxSize);
 }

}

 </source>
   
  
 
  

Get Number of Available Processors

   <source lang="java">
 

public class Main {

 public static void main(String[] args) {
   Runtime runtime = Runtime.getRuntime();
   int nrOfProcessors = runtime.availableProcessors();
   System.out.println("Number of processors available to the Java Virtual Machine: "
       + nrOfProcessors);
 }

} // Number of processors available to the Java Virtual Machine: 2

 </source>
   
  
 
  

Getting the Size of the Java Memory Heap

   <source lang="java">
 

public class Main {

 public static void main(String[] argv) throws Exception {
   long heapSize = Runtime.getRuntime().totalMemory();
   long heapMaxSize = Runtime.getRuntime().maxMemory();
   long heapFreeSize = Runtime.getRuntime().freeMemory();
 }

}

 </source>
   
  
 
  

Launch a Unix script with Java

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   String[] cmd = { "/bin/sh", "-c", "ls > hello" };
   Runtime.getRuntime().exec(cmd);
 }

}

 </source>
   
  
 
  

Minimize all programs on Windows to show the Desktop

   <source lang="java">

public class Main {

 public static void main(String args[]) throws Exception {
   Runtime.getRuntime().exec(
       new String[] {
           "cmd.exe",
           "/c",
           "\"" + System.getenv("APPDATA")
               + "\\Microsoft\\Internet Explorer\\Quick Launch\\Show Desktop.scf" + "\"" });
 }

}

 </source>
   
  
 
  

Read all information that the child process sends to its standard output stream

   <source lang="java">
 
   

import java.io.InputStream; class Run2 {

 public static void main(String[] args) throws java.io.IOException {
   if (args.length != 1) {
     System.err.println("usage: java Run pathname");
     return;
   }
   Process p = Runtime.getRuntime().exec(args[0]);
   InputStream is = p.getInputStream();
   int b;
   while ((b = is.read()) != -1)
     System.out.print((char) b);
   try {
     System.out.println("Exit status = " + p.waitFor());
   } catch (InterruptedException e) {
   }
 }

}

 </source>
   
  
 
  

Read output from a Command execution

   <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>
   
  
 
  

Registering Shutdown Hooks for Virtual Machine

   <source lang="java">

public class Main implements Runnable {

 public void run() {
   System.out.println("Shutting down");
 }
 public static void main(String[] arg) {
   Runtime runTime = Runtime.getRuntime();
   Main hook = new Main();
   runTime.addShutdownHook(new Thread(hook));
 }

}

 </source>
   
  
 
  

Runtime.getRuntime().exec

   <source lang="java">
 

class Run1 {

 public static void main(String[] args) throws java.io.IOException {
   if (args.length != 1) {
     System.err.println("usage: java Run pathname");
     return;
   }
   Process p = Runtime.getRuntime().exec(args[0]);
   try {
     System.out.println("Exit status = " + p.waitFor());
   } catch (InterruptedException e) {
   }
 }

}

 </source>
   
  
 
  

Send an 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>