Java.lang.Runtime.exec() Method

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Description

The java.lang.Runtime.exec(String[] cmdarray, String[] envp, File dir) method executes the specified command and arguments in a separate process with the specified environment and working directory. Given an array of strings cmdarray, representing the tokens of a command line, and an array of strings envp, representing "environment" variable settings, this method creates a new process in which to execute the specified command.

Starting an operating system process is highly system-dependent. Among the many things that can go wrong are −

• The operating system program file was not found.
• Access to the program file was denied.
• The working directory does not exist.

In such cases an exception will be thrown. The exact nature of the exception is system-dependent, but it will always be a subclass of IOException.

Declaration

Following is the declaration for java.lang.Runtime.exec() method

public Process exec(String[] cmdarray, String[] envp, File dir)

Parameters

• cmdarray − array containing the command to call and its arguments.

• envp − array of strings, each element of which has environment variable settings in the format name = value, or null if the subprocess should inherit the environment of the current process.

• dir − the working directory of the subprocess, or null if the subprocess should inherit the working directory of the current process.

Return Value

This method returns a new Process object for managing the subprocess

Exception

• SecurityException − If a security manager exists and its checkExec method doesn't allow creation of the subprocess

• IOException − If an I/O error occurs

• NullPointerException − If command is null

• IndexOutOfBoundsException − If cmdarray is an empty array (has length 0)

Example

This example requires a file named test.txt in our C:/ folder with the following contents −

Hello

The following example shows the usage of lang.Runtime.exec() method.

package com.tutorialspoint;

import java.io.File;

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] = "test.txt";

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

      // create a file which contains the directory of the file needed
      File dir = new File("c:/");

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

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

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

Let us compile and run the above program, this will produce the following result −

Executing notepad.exe and opening test.txt
test.txt should now open.