Executing Operating System/ Shell Commands In Java

In Java, you can execute external OS/shell commands.

There are two ways to start an operating system process/execute shell command within Java:

• java.lang.Runtime#exec(java.lang.String), since Java 1
• java.lang.ProcessBuilder, since Java 5

We will here show you both ways to execute Operating System/ Shell Commands

1. Using java.lang.Runtime
The java.lang.Runtime class allows the application to interface with the environment in which the application is running.

package com.jkoder.java.os;

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class ExecuteOSShellComandRuntime {
	public static void main(String[] args) {
		StringBuffer commandOutput = new StringBuffer();
		
		try {
			Runtime rt = Runtime.getRuntime();
			Process process = rt.exec("ls");

			process.waitFor();
			BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));

			String line = "";
			while ((line = reader.readLine()) != null) {
				commandOutput.append(line + "\n");
			}

			System.out.println(commandOutput);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

Output of the above program

total 12
drwxrwxr-x 3 jkoder jkoder 4096 May 21 19:08 bin
drwxrwxr-x 2 jkoder jkoder 4096 May 21 19:07 lib
drwxrwxr-x 3 jkoder jkoder 4096 May 16 15:34 src

2. Using java.lang.ProcessBuilder

The java.lang.ProcessBuilder.command(String… command) method Sets this process builder’s operating system program and arguments. This is a convenience method that sets the command to a string list containing the same strings as the command array, in the same order. It is not checked whether command corresponds to a valid operating system command.

package com.jkoder.java.os;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Map;

public class ExecuteOSShellComandProcessBuilder {
	public static void main(String[] args) throws java.io.IOException, java.lang.InterruptedException {

		//Create ProcessBuilder instance
        java.lang.ProcessBuilder processBuilder = new java.lang.ProcessBuilder("ls", "-l");
        
        //Set environment variables
        Map env = processBuilder.environment();
        
        final Process process = processBuilder.start();
        BufferedReader br = new BufferedReader(new InputStreamReader(process.getInputStream()));
        String line;
        while ((line = br.readLine()) != null) {
          System.out.println(line);
        }
        System.out.println("Program terminated!");
    }
}

Output of the above program

total 12
drwxrwxr-x 3 jkoder jkoder 4096 May 21 19:08 bin
drwxrwxr-x 2 jkoder jkoder 4096 May 21 19:07 lib
drwxrwxr-x 3 jkoder jkoder 4096 May 16 15:34 src
Program terminated!