Java.lang.ProcessBuilder class in Java

This class is used to create operating system processes. Each ProcessBuilder instance manages a collection of process attributes. The start() method creates a new Process instance with those attributes. The start() method can be invoked repeatedly from the same instance to create new subprocesses with identical or related attributes. 

• ProcessBuilder can be used to help create an operating system process.
• Before JDK 5.0, the only way to create a process and execute it was to use Runtime.exec() method.
• It extends the class Object.
• This class is not synchronized.

Constructor: 

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

Methods:  

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

Syntax: public List command().
Returns: this process builder's program and its arguments.
Exceptions: NullPointerException - if the argument is null.

// Java code illustrating command() method
import java.io.*;
import java.lang.*;
import java.util.*;
class ProcessBuilderDemo {
    public static void main(String[] arg) throws IOException
    {
        // creating list of process
        List<String> list = new ArrayList<String>();
        list.add("notepad.exe");

        // create the process
        ProcessBuilder build = new ProcessBuilder(list);

        // checking the command i list
        System.out.println("command: " + build.command());
    }
}

command: [notepad.exe]

2. ProcessBuilder command(List command): This method sets the process builder's operating system program and arguments. 

Syntax: public ProcessBuilder command(List command).
Returns: NA.
Exception: NullPointerException - if the argument is null.

// Java code illustrating ProcessBuilder
// command(List<String> command)
import java.io.*;
import java.lang.*;
import java.util.*;
class ProcessBuilderDemo {
    public static void main(String[] arg) throws IOException
    {
        // creating list of process
        List<String> list = new ArrayList<String>();
        list.add("notepad.exe");
        list.add("xyz.txt");

        // create the process
        ProcessBuilder build = new ProcessBuilder(list);

        // checking the command in list
        System.out.println("command: " + build.command());
    }
}

command: [notepad.exe, xyz.txt]

3. ProcessBuilder directory(File directory): This method sets the process builder's working directory. Subprocesses subsequently started by object's start() method will use it as their working directory. The argument may be null - which means to use the working directory of the current Java process, usually, the directory named by the system property user.dir, as the working directory of the child process. 

Syntax: public ProcessBuilder directory(File directory).
Returns: this process builder.
Exception: NA.

// Java code illustrating directory() method
import java.io.*;
import java.lang.*;
import java.util.*;
class ProcessBuilderDemo {
    public static void main(String[] arg) throws IOException
    {
        // creating list of process
        List<String> list = new ArrayList<String>();
        list.add("notepad.exe");
        list.add("abc.txt");

        // creating the process
        ProcessBuilder build = new ProcessBuilder(list);

        // setting the directory
        build.directory(new File("src"));

        // checking the directory, on which currently
        // working on
        System.out.println("directory: "
                           + build.directory());
    }
}

directory: src

4. Map environment(): This method returns a string map view of the process builder's environment. Whenever a process builder is created, the environment is initialized to a copy of the current process environment. Subprocesses subsequently started by the object's start() method will use this map as their environment. 

Syntax: public Map environment()
Returns: this process builder's environment
Exception: SecurityException - if a security manager exists 
and its checkPermission method doesn't allow access to the process environment.

// Java code illustrating environment() method
import java.io.*;
import java.util.*;
class ProcessBuilderDemo {
    public static void main(String[] arg) throws IOException
    {
        // creating the process
        ProcessBuilder pb = new ProcessBuilder();

        // map view of this process builder's environment
        Map<String, String> envMap = pb.environment();

        // checking map view of environment
        for (Map.Entry<String, String> entry :
             envMap.entrySet()) {
            // checking key and value separately
            System.out.println("Key = " + entry.getKey()
                               + ", Value = "
                               + entry.getValue());
        }
    }
}

Output: 

Key = PATH, Value = /usr/bin:/bin:/usr/sbin:/sbin
Key = JAVA_MAIN_CLASS_14267, Value = ProcessBuilderDemo
Key = J2D_PIXMAPS, Value = shared
Key = SHELL, Value = /bin/bash
Key = JAVA_MAIN_CLASS_11858, Value = org.netbeans.Main
Key = USER, Value = abhishekverma
Key = TMPDIR, Value = /var/folders/9z/p63ysmfd797clc0468vvy4980000gn/T/
Key = SSH_AUTH_SOCK, Value = /private/tmp/com.apple.launchd.uWvCfYQWBP/Listeners
Key = XPC_FLAGS, Value = 0x0
Key = LD_LIBRARY_PATH, Value = /Library/Java/JavaVirtualMachines
/jdk1.8.0_121.jdk/Contents/Home/jre/lib/
amd64:/Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk
/Contents/Home/jre/lib/i386:
Key = __CF_USER_TEXT_ENCODING, Value = 0x1F5:0x0:0x0
Key = Apple_PubSub_Socket_Render, Value = /private/tmp/com.apple.launchd.weuNq4pAfF/Render
Key = LOGNAME, Value = abhishekverma
Key = LC_CTYPE, Value = UTF-8
Key = XPC_SERVICE_NAME, Value = 0
Key = PWD, Value = /
Key = SHLVL, Value = 1
Key = HOME, Value = /Users/abhishekverma
Key = _, Value = /Library/Java/JavaVirtualMachines/
jdk1.8.0_121.jdk/Contents/Home/bin/java

Understanding the above output: The output is the map view of the subprocess build upon. The above output varies from user to user totally depends upon the operating system and user.

5. boolean redirectErrorStream(): This method tells whether the process builder merges standard error and standard output. If this property is true, then any error output generated by subprocesses subsequently started by the object's start() method will be merged with the standard output, so that both can be read using the Process.getInputStream() method. It makes it easier to correlate error messages with the corresponding output. The initial value is false. 

Syntax: public boolean redirectErrorStream().
Returns: this process builder's redirectErrorStream property.
Exception: NA.

// Java code illustrating redirectErrorStream() method
import java.io.*;
import java.lang.*;
import java.util.*;
class ProcessBuilderDemo {
    public static void main(String[] arg) throws IOException
    {

        // creating list of commands
        List list = new ArrayList();

        list.add("notepad.exe");
        list.add("xyz.txt");

        // creating the process
        ProcessBuilder build = new ProcessBuilder(list);

        // checking if error stream is redirected
        System.out.println(build.redirectErrorStream());
    }
}

Output: 

false

6. ProcessBuilder redirectErrorStream(boolean redirectErrorStream): This method sets this process builder's redirectErrorStream property. If this property is true, then any error output generated by subprocesses subsequently started by this object's start() method will be merged with the standard output so that both can be read using the Process.getInputStream() method. This makes it easier to correlate error messages with the corresponding output. The initial value is false. 

Syntax: public ProcessBuilder redirectErrorStream(boolean redirectErrorStream).
Returns: this process builder.
Exception: NA.

// Java code illustrating redirectErrorStream(boolean
// redirectErrorStream) method
import java.io.*;
import java.lang.*;
import java.util.*;
class ProcessBuilderDemo {
    public static void main(String[] arg) throws IOException
    {

        // creating list of commands
        List list = new ArrayList();

        list.add("notepad.exe");
        list.add("xyz.txt");

        // creating the process
        ProcessBuilder build = new ProcessBuilder(list);

        // redirecting error stream
        build.redirectErrorStream(true);

        // checking if error stream is redirected
        System.out.println(build.redirectErrorStream());
    }
}

Output: 

true

Process start(): This method starts a new process using the attributes of the 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(). This method checks that the command is a valid operating system command. Which commands are valid is system-dependent, but at the very least the command must be a non-empty list of non-null strings. If there is a security manager, its checkExec method is called with the first component of this object's command array as its argument. It may result in a SecurityException being thrown. 

Syntax: public Process start().
Returns: a new Process object for managing the subprocess.
Exception: NullPointerException - If an element of the command list is null
IndexOutOfBoundsException - If the command is an empty list (has size 0).
SecurityException - If a security manager exists 
and its checkExec method doesn't allow creation of the subprocess.
IOException - If an I/O error occurs.

// Java code illustrating start() method
import java.io.*;
import java.lang.*;
import java.util.*;
class ProcessBuilderDemo {
    public static void main(String[] arg) throws IOException
    {
        // creating list of commands
        List<String> commands = new ArrayList<String>();
        commands.add("ls"); // command
        commands.add("-l"); // command
        commands.add(
            "/Users/abhishekverma"); // command in Mac OS

        // creating the process
        ProcessBuilder pb = new ProcessBuilder(commands);

        // starting the process
        Process process = pb.start();

        // for reading the output from stream
        BufferedReader stdInput
            = new BufferedReader(new InputStreamReader(
                process.getInputStream()));
        String s = null;
        while ((s = stdInput.readLine()) != null) {
            System.out.println(s);
        }
    }
}

Output: 

total 0
drwxr-xr-x  10 abhishekverma  staff   340 Jun 20 02:24 AndroidStudioProjects
drwx------@ 22 abhishekverma  staff   748 Jun 20 03:00 Desktop
drwx------@  7 abhishekverma  staff   238 Apr 29 22:03 Documents
drwx------+ 27 abhishekverma  staff   918 Jun 20 03:01 Downloads
drwx------@ 65 abhishekverma  staff  2210 Jun 18 20:48 Library
drwx------+  3 abhishekverma  staff   102 Mar 28 13:08 Movies
drwx------+  4 abhishekverma  staff   136 Apr  8 04:51 Music
drwxr-xr-x   4 abhishekverma  staff   136 Jun 19 15:01 NetBeansProjects
drwx------+  5 abhishekverma  staff   170 Apr 10 09:46 Pictures
drwxr-xr-x+  6 abhishekverma  staff   204 Jun 18 20:45 Public
-rw-r--r--   1 abhishekverma  staff     0 Apr 15 19:23 newreactjs.jsx

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

Syntax: public ProcessBuilder inheritIO().
Returns: this process builder.
Exception: NA.

// Java code illustrating inheritIO() method
import java.io.*;
import java.lang.*;
import java.util.*;
class ProcessBuilderDemo {
    public static void main(String[] arg)
        throws IOException, InterruptedException
    {
        ProcessBuilder pb = new ProcessBuilder(
            "echo", "Hello GeeksforGeeks\n"
                        + "This is ProcessBuilder Example");
        pb.inheritIO();
        Process process = pb.start();
        process.waitFor();
    }
}

Output: 

Hello GeeksforGeeks
This is ProcessBuilder Example