ProcessBuilder start() in Java

start(): This method is available in the java.lang.ProcessBuilder class of Java.

Syntax:

Process java.lang.ProcessBuilder.start() throws IOException

This method starts a new process using the attributes of this process builder.

The new process will invoke the command and arguments given by command(),in a working directory as given by directory(),with a process environment as given by environment().

Parameters: NA

Returns: a new Process object for managing the subprocess.

Throws:

1. NullPointerException - if an element of the command list is null.

2. IndexOutOfBoundsException - if the command is an empty list.

3. SecurityException - if a security manager exists and

a). its checkExecmethod doesn't allow creation of the subprocess.

b). the standard input to the subprocess was redirected from a file and the security manager's checkRead method denies read access to the file.

c). the standard output or standard error of thesubprocess was redirected to a fileand the security manager's checkWrite method denies write access to the file.

4. UnsupportedOperationException - If the operating system does not support the creation of processes.

5. IOException - if an I/O error occurs.

Approach 1: When no exception

Java

package com.ProcessBuilder;

import java.io.IOException;

public class ProcessBuilderstart {
    public static void main(String[] args) throws IOException {

        String commands[] = { "notepad.exe" };
        ProcessBuilder processBuilder = 
                     new ProcessBuilder(commands);

        System.out.println(processBuilder.start());
    }
}

Output:

Process[pid=5704, exitValue="not exited"]

Approach 2: NullPointerException 

Java

package com.ProcessBuilder;

import java.io.IOException;

public class ProcessBuilderstart {
    public static void main(String[] args) throws IOException {

        String commands[] = null;
        ProcessBuilder processBuilder = 
                     new ProcessBuilder(commands);

        System.out.println(processBuilder.start());
    }
}

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot read the array length because "command" is null
	at java.base/java.lang.ProcessBuilder.<init>(ProcessBuilder.java:229)
	at com.ProcessBuilder.ProcessBuilderstart.main(ProcessBuilderstart.java:9)

Approach 3: IndexOutOfBoundsException

Java

package com.ProcessBuilder;

import java.io.IOException;

public class ProcessBuilderstart {
    public static void main(String[] args) throws IOException {

        String commands[] = {};
        ProcessBuilder processBuilder = 
                         new ProcessBuilder(commands);

        System.out.println(processBuilder.start());
    }
}

Output:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
	at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1094)
	at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1073)
	at com.ProcessBuilder.ProcessBuilderstart.main(ProcessBuilderstart.java:11)

Approach 4: IOException 

Java

package com.ProcessBuilder;

import java.io.IOException;

public class ProcessBuilderstart {
    public static void main(String[] args) throws IOException {

        String commands[] = { "hello.exe" };
        ProcessBuilder processBuilder = 
                            new ProcessBuilder(commands);

        System.out.println(processBuilder.start());
    }
}

Output:

Exception in thread "main" java.io.IOException: Cannot run program "hello.exe": CreateProcess error=2, The system cannot find the file specified
	at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1142)
	at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1073)
	at com.ProcessBuilder.ProcessBuilderstart.main(ProcessBuilderstart.java:11)
Caused by: java.io.IOException: CreateProcess error=2, The system cannot find the file specified
	at java.base/java.lang.ProcessImpl.create(Native Method)
	at java.base/java.lang.ProcessImpl.<init>(ProcessImpl.java:483)
	at java.base/java.lang.ProcessImpl.start(ProcessImpl.java:158)
	at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1109)
	... 2 more

Some methods of ProcessBuilder class

ProcessBuilder.ProcessBuilder(String...): This method constructs a process builder with the specified operating system program and arguments.

ProcessBuilder.ProcessBuilder(List<String>): This method constructs a process builder with the specified operating system program and arguments.

command(): This method returns this process builder's operating system program and arguments.

command(List<String>): This method sets this process builder's operating system program and arguments.

command(String...): This method sets this process builder's operating system program and arguments. 

directory(): This method returns this process builder's working directory.

directory(File): This method sets this process builder's working directory.

environment(): This method returns a string map view of this process builder's environment.

inheritIO(): This method sets the source and destination for subprocess standard I/O to be the same as those of the current Java process.

redirectError(): This method returns this process builder's standard error destination.

redirectError(File): This method sets this process builder's standard error destination to a file.

redirectError(Redirect): This method sets this process builder's standard error destination.

redirectErrorStream(): This method tells whether this process builder merges standard error and standard output.

redirectErrorStream(boolean): This method sets this process builder's redirectErrorStream property.

redirectInput(): This method returns this process builder's standard input source.

redirectInput(File): This method sets this process builder's standard input source to a file.

redirectInput(Redirect): This method sets this process builder's standard input source.

redirectOutput(): This method returns this process builder's standard output destination.

redirectOutput(File): This method sets this process builder's standard output destination to a file.

redirectOutput(Redirect): This method sets this process builder's standard output destination.

start(): This method starts a new process using the attributes of this process builder.

ProcessBuilder.startPipeline(List<ProcessBuilder>): his method starts a Process for each ProcessBuilder, creating a pipeline of processes linked by their standard output and standard input streams.