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
// Java code illustrating command() methodimport 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
// 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
// Java code illustrating directory() methodimport 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
// Java code illustrating environment() methodimport 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
// Java code illustrating redirectErrorStream() methodimport 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
// Java code illustrating redirectErrorStream(boolean// redirectErrorStream) methodimport 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
// Java code illustrating start() methodimport 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
// Java code illustrating inheritIO() methodimport 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 Lazyroar\n" + "This is ProcessBuilder Example"); pb.inheritIO(); Process process = pb.start(); process.waitFor(); }} |
Output:
Hello Lazyroar This is ProcessBuilder Example
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