Java Runtime exec() Method

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Description

The Java 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: Opening a File in Notepad

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

 Hello 

The following example shows the usage of Java Runtime exec() method. In this program, we've a string array. Notepad.exe and test.txt entries are added. We've created a Process object for notepad executable using exec() method. This will invoke the notepad application and test.txt will be opened. If some exception occurs, a corresponding stack trace is printed with error message. If test.txt is not present in current classpath, then Notepad will report error for non-existing file.

 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(); } } } 

Output

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. 

Example: Opening Calculator

The following example shows the usage of Java Runtime exec() method. In this program, we've a string array. calc.exe entry is added. We've created a Process object for calculator executable using exec() method. This will invoke the calculator application. If some exception occurs, a corresponding stack trace is printed with error message.

 package com.tutorialspoint; import java.io.File; public class RuntimeDemo { public static void main(String[] args) { try { // create a new array of 1 string String[] cmdArray = new String[1]; // first argument is the program we want to open cmdArray[0] = "calc.exe"; // print a message System.out.println("Executing calc.exe"); // 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); } catch (Exception ex) { ex.printStackTrace(); } } } 

Output

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

 Executing calc.exe 

Example: Opening Windows Explorer

The following example shows the usage of Java Runtime exec() method. In this program, we've a string array. explorer.exe entry is added. We've created a Process object for explorer executable using exec() method. This will invoke the windows explorer application. If some exception occurs, a corresponding stack trace is printed with error message.

 package com.tutorialspoint; import java.io.File; public class RuntimeDemo { public static void main(String[] args) { try { // create a new array of 1 string String[] cmdArray = new String[1]; // first argument is the program we want to open cmdArray[0] = "explorer.exe"; // print a message System.out.println("Executing explorer.exe"); // 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); } catch (Exception ex) { ex.printStackTrace(); } } } 

Output

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

 Executing calc.exe