Java.lang.Process class in Java

Difficulty Level : Medium
Last Updated : 19 Jun, 2017

The abstract Process class a process- that is, an executing program. Methods provided by the Process is used to perform input, output, waiting for the process o complete, checking exit status of the process and destroying process.

It extends class Object.
It is used primarily as a superclass for the type of object created by exec() in the Runtime class.
ProcessBuilder.start() and Runtime.getRuntime.exec() methods creates a native process and return an instance of a subclass of Process that can be used to control the process and obtain information about it.
ProcessBuilder.start() is the most preferred way to create process.

ProcessBuilder.start() vs Runtime.getRuntime.exec(): ProcessBuilder allows us to redirect the standard error of the child process into its standard output. Now we don’t need two separate threads one reading from stdout and one reading from stderr.

Constructor

Process(): This is the only constructor.

Methods:

void destroy(): Kills the subprocess.

Syntax: public abstract void destroy().
Returns: NA.
Exception: NA.

// Java code illustrating destroy() 
// method for windows operating system
public class ProcessDemo 
    public static void main(String[] args) 
    {
        try 
        {
              
            // create a new process
            System.out.println("Creating Process");
              
            ProcessBuilder builder = new ProcessBuilder("notepad.exe");
            Process pro = builder.start();
      
            // wait 10 seconds
            System.out.println("Waiting");
            Thread.sleep(10000);
      
            // kill the process
            pro.destroy();
            System.out.println("Process destroyed");
      
        } 
            catch (Exception ex) 
        {
            ex.printStackTrace();
        }
    }
}

Output:

Creating Process
Waiting
Process destroyed

// Java code illustrating destroy()
// method for Mac Operating System
import java.lang.*;
import java.io.*;
class ProcessDemo
{
    public static void main(String arg[]) throws IOException, Exception
    {
        System.out.println("Creating process");
              
        //creating process
        ProcessBuilder p = new ProcessBuilder(new String[] 
                        {"open", "/Applications/Facetime.app"});
        Process pro = p.start();
              
        //waiting for 10 second
        Thread.sleep(10000);
              
        System.out.println("destroying process");
              
        //destroying process
        pro.destroy();
    }
}

Output:

Creating process
destroying process

int exitValue(): This method returns the exit value for the subprocess.

Syntax: public abstract int exitValue().
Returns: This method returns the exit value of 
the subprocess represented by this Process object. 
By convention, the value 0 indicates normal termination.
Exception: IllegalThreadStateException ,
if the subprocess represented by this Process object has not yet terminated.

// Java code illustrating exitValue() method
public class ProcessDemo 
{
    public static void main(String[] args)
    {
        try 
        {
            // create a new process
            System.out.println("Creating Process");
              
            ProcessBuilder builder = new ProcessBuilder("notepad.exe");
            Process pro = builder.start();
      
            // kill the process
            pro.destroy();
              
            // checking the exit value of subprocess
            System.out.println("exit value: " + pro.exitValue());
      
        } 
            catch (Exception ex) 
        {
            ex.printStackTrace();
        }
    }
}

Output:

Creating Process
1

abstract InputStream getErrorStream(): This method gets the input stream of the subprocess.

Syntax: public abstract InputStream getInputStream().
Returns: input stream that reads input from the process out output stream.
Exception: NA.

// Java code illustrating
// getInputStream() method
import java.lang.*;
import java.io.*;
class ProcessDemo
{
    public static void main(String arg[]) throws IOException, Exception
    {
        // creating the process
        Runtime r = Runtime.getRuntime();
          
        // shell script for loop from 1 to 3
        String[] nargs = {"sh", "-c", "for i in 
                1 2 3; do echo $i; done"};               
        Process p = r.exec(nargs);
      
        BufferedReader is = 
            new BufferedReader(new InputStreamReader(p.getInputStream()));
        String line;
          
        // reading the output
        while ((line = is.readLine()) != null)
          
        System.out.println(line);
    }
}

Output:

1
2
3

abstract OutputStream getOutputStream(): This method gets the output stream of the subprocess. Output to the stream is piped into the standard input stream of the process represented by this Process object.

Syntax: public abstract OutputStream getOutputStream()
Returns: the output stream connected to the normal input of the subprocess.
Exception: NA.

// Java code illustrating 
// getOutputStream() method
import java.io.BufferedOutputStream;
import java.io.OutputStream;
  
public class ProcessDemo 
{
    public static void main(String[] args)
    {
        try 
        {
            // create a new process
            System.out.println("Creating Process");
            Process p = Runtime.getRuntime().exec("notepad.exe");
      
            // get the output stream
            OutputStream out = p.getOutputStream();
      
            // close the output stream
            System.out.println("Closing the output stream");
            out.close();
        } 
            catch (Exception ex) 
        {
            ex.printStackTrace();
        }
    }
}

Output:

Creating Process...
Closing the output stream...

abstract InputStream getErrorStream(): It returns an input stream that reads input from the process err output stream.

Syntax: public abstract InputStream getErrorStream().
Returns: the input stream connected to the error stream of the subprocess.
Exception: NA.

// Java code illustrating 
// getErrorStream() method
import java.io.InputStream;
  
public class ProcessDemo
{
    public static void main(String[] args) 
    {
        try 
        {
            // create a new process
            System.out.println("Creating Process");
              
            Process p = Runtime.getRuntime().exec("notepad.exe");
      
            // get the error stream of the process and print it
            InputStream error = p.getErrorStream();
              
            for (int i = 0; i < error.available(); i++) 
            {
                System.out.println("" + error.read());
            }
      
            // wait for 10 seconds and then destroy the process
            Thread.sleep(10000);
            p.destroy();
      
        } 
          
        catch (Exception ex) 
        {
            ex.printStackTrace();
        }
    }
}

Output:

Creating Process

int waitFor(): Returns the exit code returned by the process. This method does not return until the process on which it is called terminates.

Syntax: public int waitFor().
Returns: the exit value of the process. By convention, 0 indicates normal termination.
Exception: throws InterruptedException.

// Java code illustrating 
// waitFor() method
  
public class ProcessDemo 
{
    public static void main(String[] args) 
    {
        try 
        {
            // create a new process
            System.out.println("Creating Process");
            Process p = Runtime.getRuntime().exec("notepad.exe");
      
            // cause this process to stop
                // until process p is terminated
            p.waitFor();
      
            // when you manually close notepad.exe
                // program will continue here
            System.out.println("Waiting over");
        } 
        catch (Exception ex) 
        {
            ex.printStackTrace();
        }
    }
}

Output:

Creating Process...
Waiting over.

This article is contributed by Abhishek Verma. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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