Class ProcessBuilder

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.

Each process builder manages these process attributes:

• a command, a list of strings which signifies the external program file to be invoked and its arguments, if any. Which string lists represent a valid operating system command is system-dependent. For example, it is common for each conceptual argument to be an element in this list, but there are operating systems where programs are expected to tokenize command line strings themselves - on such a system a Java implementation might require commands to contain exactly two elements.
• an environment, which is a system-dependent mapping from variables to values. The initial value is a copy of the environment of the current process (see System.getenv()).
• a working directory. The default value is the current working directory of the current process, usually the directory named by the system property user.dir.
• a source of standard input. By default, the subprocess reads input from a pipe. Java code can access this pipe via the output stream returned by Process.getOutputStream(). However, standard input may be redirected to another source using redirectInput. In this case, Process.getOutputStream() will return a null output stream, for which:
  • the write methods always throw IOException
  • the close method does nothing
• a destination for standard output and standard error. By default, the subprocess writes standard output and standard error to pipes. Java code can access these pipes via the input streams returned by Process.getInputStream() and Process.getErrorStream(). However, standard output and standard error may be redirected to other destinations using redirectOutput and redirectError. In this case, Process.getInputStream() and/or Process.getErrorStream() will return a null input stream, for which:
  • the read methods always return -1
  • the available method always returns 0
  • the close method does nothing
• a redirectErrorStream property. Initially, this property is false, meaning that the standard output and error output of a subprocess are sent to two separate streams, which can be accessed using the Process.getInputStream() and Process.getErrorStream() methods.

  If the value is set to true, then:

  • standard error is merged with the standard output and always sent to the same destination (this makes it easier to correlate error messages with the corresponding output)
  • the common destination of standard error and standard output can be redirected using redirectOutput
  • any redirection set by the redirectError method is ignored when creating a subprocess
  • the stream returned from Process.getErrorStream() will always be a null input stream

Modifying a process builder's attributes will affect processes subsequently started by that object's start() method, but will never affect previously started processes or the Java process itself.

Most error checking is performed by the start() method. It is possible to modify the state of an object so that start() will fail. For example, setting the command attribute to an empty list will not throw an exception unless start() is invoked.

Note that this class is not synchronized. If multiple threads access a ProcessBuilder instance concurrently, and at least one of the threads modifies one of the attributes structurally, it must be synchronized externally.

Starting a new process which uses the default working directory and environment is easy:

Process p = new ProcessBuilder("myCommand", "myArg").start();

Here is an example that starts a process with a modified working directory and environment, and redirects standard output and error to be appended to a log file:

ProcessBuilder pb =
   new ProcessBuilder("myCommand", "myArg1", "myArg2");
 Map<String, String> env = pb.environment();
 env.put("VAR1", "myValue");
 env.remove("OTHERVAR");
 env.put("VAR2", env.get("VAR1") + "suffix");
 pb.directory(new File("myDir"));
 File log = new File("log");
 pb.redirectErrorStream(true);
 pb.redirectOutput(Redirect.appendTo(log));
 Process p = pb.start();
 assert pb.redirectInput() == Redirect.PIPE;
 assert pb.redirectOutput().file() == log;
 assert p.getInputStream().read() == -1;

To start a process with an explicit set of environment variables, first call Map.clear() before adding environment variables.

Constructors

ProcessBuilder

public ProcessBuilder(List<String> command)

Constructs a process builder with the specified operating system program and arguments. This constructor does not make a copy of the command list. Subsequent updates to the list will be reflected in the state of the process builder. It is not checked whether command corresponds to a valid operating system command.

Parameters:

command - the list containing the program and its arguments

Throws:

NullPointerException - if the argument is null

ProcessBuilder

public ProcessBuilder(String... command)

Constructs a process builder with the specified operating system program and arguments. This is a convenience constructor that sets the process builder's 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.

Parameters:

command - a string array containing the program and its arguments

Methods

command

public ProcessBuilder command(List<String> command)

Sets this process builder's operating system program and arguments. This method does not make a copy of the command list. Subsequent updates to the list will be reflected in the state of the process builder. It is not checked whether command corresponds to a valid operating system command.

Parameters:

command - the list containing the program and its arguments

Returns:

this process builder

Throws:

NullPointerException - if the argument is null

command

public ProcessBuilder command(String... command)

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.

Parameters:

command - a string array containing the program and its arguments

Returns:

this process builder

command

public List<String> command()

Returns this process builder's operating system program and arguments. The returned list is not a copy. Subsequent updates to the list will be reflected in the state of this process builder.

Returns:

this process builder's program and its arguments

environment

public Map<String,String> environment()

Returns:

this process builder's environment

Throws:

SecurityException - if a security manager exists and its checkPermission method doesn't allow access to the process environment

See Also:

Runtime.exec(String[],String[],java.io.File), System.getenv()

directory

public File directory()

Returns this process builder's working directory. Subprocesses subsequently started by this object's start() method will use this as their working directory. The returned value may be null -- this 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.

Returns:

this process builder's working directory

directory

public ProcessBuilder directory(File directory)

Sets this process builder's working directory. Subprocesses subsequently started by this object's start() method will use this as their working directory. The argument may be null -- this 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.

Parameters:

directory - the new working directory

Returns:

this process builder

redirectInput

public ProcessBuilder redirectInput(ProcessBuilder.Redirect source)

Parameters:

source - the new standard input source

Returns:

this process builder

Throws:

IllegalArgumentException - if the redirect does not correspond to a valid source of data, that is, has type WRITE or APPEND

Since:

1.7

redirectOutput

public ProcessBuilder redirectOutput(ProcessBuilder.Redirect destination)

Parameters:

destination - the new standard output destination

Returns:

this process builder

Throws:

IllegalArgumentException - if the redirect does not correspond to a valid destination of data, that is, has type READ

Since:

1.7

redirectError

public ProcessBuilder redirectError(ProcessBuilder.Redirect destination)

Parameters:

destination - the new standard error destination

Returns:

this process builder

Throws:

IllegalArgumentException - if the redirect does not correspond to a valid destination of data, that is, has type READ

Since:

1.7

redirectInput

public ProcessBuilder redirectInput(File file)

Parameters:

file - the new standard input source

Returns:

this process builder

Since:

1.7

redirectOutput

public ProcessBuilder redirectOutput(File file)

Parameters:

file - the new standard output destination

Returns:

this process builder

Since:

1.7

redirectError

public ProcessBuilder redirectError(File file)

Parameters:

file - the new standard error destination

Returns:

this process builder

Since:

1.7

redirectInput

public ProcessBuilder.Redirect redirectInput()

Returns this process builder's standard input source. Subprocesses subsequently started by this object's start() method obtain their standard input from this source. The initial value is Redirect.PIPE.

Returns:

this process builder's standard input source

Since:

1.7

redirectOutput

public ProcessBuilder.Redirect redirectOutput()

Returns this process builder's standard output destination. Subprocesses subsequently started by this object's start() method redirect their standard output to this destination. The initial value is Redirect.PIPE.

Returns:

this process builder's standard output destination

Since:

1.7

redirectError

public ProcessBuilder.Redirect redirectError()

Returns this process builder's standard error destination. Subprocesses subsequently started by this object's start() method redirect their standard error to this destination. The initial value is Redirect.PIPE.

Returns:

this process builder's standard error destination

Since:

1.7

inheritIO

public ProcessBuilder inheritIO()

pb.inheritIO()

pb.redirectInput(Redirect.INHERIT)
   .redirectOutput(Redirect.INHERIT)
   .redirectError(Redirect.INHERIT)

Returns:

this process builder

Since:

1.7

redirectErrorStream

public boolean redirectErrorStream()

Returns:

this process builder's redirectErrorStream property

redirectErrorStream

public ProcessBuilder redirectErrorStream(boolean redirectErrorStream)

Parameters:

redirectErrorStream - the new property value

Returns:

this process builder

start

public Process start()
              throws IOException

Returns:

a new Process object for managing the subprocess

Throws:

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, or
• the standard input to the subprocess was redirected from a file and the security manager's checkRead method denies read access to the file, or
• the standard output or standard error of the subprocess was redirected to a file and the security manager's checkWrite method denies write access to the file

IOException - if an I/O error occurs

See Also:

Runtime.exec(String[], String[], java.io.File)