ProcessBuilder
public
final
class
ProcessBuilder
extends Object
java.lang.Object | |
↳ | java.lang.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 usingredirectInput
. In this case,Process#getOutputStream()
will return a null output stream, for which: - 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()
andProcess#getErrorStream()
. However, standard output and standard error may be redirected to other destinations usingredirectOutput
andredirectError
. In this case,Process#getInputStream()
and/orProcess#getErrorStream()
will return a null input stream, for which: - 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 theProcess#getInputStream()
andProcess.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.
Summary
Nested classes | |
---|---|
class |
ProcessBuilder.Redirect
Represents a source of subprocess input or a destination of subprocess output. |
Public constructors | |
---|---|
ProcessBuilder(List<String> command)
Constructs a process builder with the specified operating system program and arguments. |
|
ProcessBuilder(String... command)
Constructs a process builder with the specified operating system program and arguments. |
Public methods | |
---|---|
List<String>
|
command()
Returns this process builder's operating system program and arguments. |
ProcessBuilder
|
command(List<String> command)
Sets this process builder's operating system program and arguments. |
ProcessBuilder
|
command(String... command)
Sets this process builder's operating system program and arguments. |
ProcessBuilder
|
directory(File directory)
Sets this process builder's working directory. |
File
|
directory()
Returns this process builder's working directory. |
Map<String, String>
|
environment()
Returns a string map view of this process builder's environment. |
ProcessBuilder
|
inheritIO()
Sets the source and destination for subprocess standard I/O to be the same as those of the current Java process. |
ProcessBuilder
|
redirectError(ProcessBuilder.Redirect destination)
Sets this process builder's standard error destination. |
ProcessBuilder.Redirect
|
redirectError()
Returns this process builder's standard error destination. |
ProcessBuilder
|
redirectError(File file)
Sets this process builder's standard error destination to a file. |
boolean
|
redirectErrorStream()
Tells whether this process builder merges standard error and standard output. |
ProcessBuilder
|
redirectErrorStream(boolean redirectErrorStream)
Sets this process builder's |
ProcessBuilder
|
redirectInput(File file)
Sets this process builder's standard input source to a file. |
ProcessBuilder.Redirect
|
redirectInput()
Returns this process builder's standard input source. |
ProcessBuilder
|
redirectInput(ProcessBuilder.Redirect source)
Sets this process builder's standard input source. |
ProcessBuilder
|
redirectOutput(ProcessBuilder.Redirect destination)
Sets this process builder's standard output destination. |
ProcessBuilder.Redirect
|
redirectOutput()
Returns this process builder's standard output destination. |
ProcessBuilder
|
redirectOutput(File file)
Sets this process builder's standard output destination to a file. |
Process
|
start()
Starts a new process using the attributes of this process builder. |
Inherited methods | |
---|---|
Public 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 |
List : 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 |
String : a string array containing the program and its arguments |
Public methods
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 | |
---|---|
List<String> |
this process builder's program and its arguments |
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 |
List : the list containing the program and its arguments |
Returns | |
---|---|
ProcessBuilder |
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 |
String : a string array containing the program and its arguments |
Returns | |
---|---|
ProcessBuilder |
this process builder |
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 |
File : the new working directory |
Returns | |
---|---|
ProcessBuilder |
this process builder |
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 | |
---|---|
File |
this process builder's working directory |
environment
public Map<String, String> environment ()
Returns a string map view of this process builder's environment.
Whenever a process builder is created, the environment is
initialized to a copy of the current process environment (see
System#getenv()
). Subprocesses subsequently started by
this object's start()
method will use this map as
their environment.
The returned object may be modified using ordinary Map
operations. These modifications will be
visible to subprocesses started via the start()
method. Two ProcessBuilder
instances always
contain independent process environments, so changes to the
returned map will never be reflected in any other
ProcessBuilder
instance or the values returned by
System.getenv
.
If the system does not support environment variables, an empty map is returned.
The returned map does not permit null keys or values.
Attempting to insert or query the presence of a null key or
value will throw a NullPointerException
.
Attempting to query the presence of a key or value which is not
of type String
will throw a ClassCastException
.
The behavior of the returned map is system-dependent. A
system may not allow modifications to environment variables or
may forbid certain variable names or values. For this reason,
attempts to modify the map may fail with
UnsupportedOperationException
or
IllegalArgumentException
if the modification is not permitted by the operating system.
Since the external format of environment variable names and values is system-dependent, there may not be a one-to-one mapping between them and Java's Unicode strings. Nevertheless, the map is implemented in such a way that environment variables which are not modified by Java code will have an unmodified native representation in the subprocess.
The returned map and its collection views may not obey the
general contract of the Object#equals
and
Object#hashCode
methods.
The returned map is typically case-sensitive on all platforms.
If a security manager exists, its
checkPermission
method
is called with a
RuntimePermission
("getenv.*")
permission.
This may result in a SecurityException
being thrown.
When passing information to a Java subprocess, system properties are generally preferred over environment variables.
Returns | |
---|---|
Map<String, String> |
this process builder's environment |
Throws | |
---|---|
SecurityException |
if a security manager exists and its
checkPermission
method doesn't allow access to the process environment |
inheritIO
public ProcessBuilder inheritIO ()
Sets the source and destination for subprocess standard I/O to be the same as those of the current Java process.
This is a convenience method. An invocation of the form
pb.inheritIO()
pb.redirectInput(Redirect.INHERIT)
.redirectOutput(Redirect.INHERIT)
.redirectError(Redirect.INHERIT)
system()
.
Returns | |
---|---|
ProcessBuilder |
this process builder |
redirectError
public ProcessBuilder redirectError (ProcessBuilder.Redirect destination)
Sets this process builder's standard error destination.
Subprocesses subsequently started by this object's start()
method send their standard error to this destination.
If the destination is Redirect.PIPE
(the initial value), then the error output of a subprocess
can be read using the input stream returned by Process.getErrorStream()
.
If the destination is set to any other value, then
Process#getErrorStream()
will return a
null input stream.
If the redirectErrorStream
attribute has been set true
, then the redirection set
by this method has no effect.
Parameters | |
---|---|
destination |
ProcessBuilder.Redirect : the new standard error destination |
Returns | |
---|---|
ProcessBuilder |
this process builder |
Throws | |
---|---|
IllegalArgumentException |
if the redirect does not correspond to a valid
destination of data, that is, has type
READ |
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 | |
---|---|
ProcessBuilder.Redirect |
this process builder's standard error destination |
redirectError
public ProcessBuilder redirectError (File file)
Sets this process builder's standard error destination to a file.
This is a convenience method. An invocation of the form
redirectError(file)
behaves in exactly the same way as the invocation
redirectError
(Redirect.to(file))
.
Parameters | |
---|---|
file |
File : the new standard error destination |
Returns | |
---|---|
ProcessBuilder |
this process builder |
redirectErrorStream
public boolean redirectErrorStream ()
Tells whether this process builder merges standard error and standard output.
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
.
Returns | |
---|---|
boolean |
this process builder's redirectErrorStream property |
redirectErrorStream
public ProcessBuilder redirectErrorStream (boolean redirectErrorStream)
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
.
Parameters | |
---|---|
redirectErrorStream |
boolean : the new property value |
Returns | |
---|---|
ProcessBuilder |
this process builder |
redirectInput
public ProcessBuilder redirectInput (File file)
Sets this process builder's standard input source to a file.
This is a convenience method. An invocation of the form
redirectInput(file)
behaves in exactly the same way as the invocation
redirectInput
(Redirect.from(file))
.
Parameters | |
---|---|
file |
File : the new standard input source |
Returns | |
---|---|
ProcessBuilder |
this process builder |
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 | |
---|---|
ProcessBuilder.Redirect |
this process builder's standard input source |
redirectInput
public ProcessBuilder redirectInput (ProcessBuilder.Redirect source)
Sets this process builder's standard input source.
Subprocesses subsequently started by this object's start()
method obtain their standard input from this source.
If the source is Redirect.PIPE
(the initial value), then the standard input of a
subprocess can be written to using the output stream
returned by Process#getOutputStream()
.
If the source is set to any other value, then
Process#getOutputStream()
will return a
null output stream.
Parameters | |
---|---|
source |
ProcessBuilder.Redirect : the new standard input source |
Returns | |
---|---|
ProcessBuilder |
this process builder |
Throws | |
---|---|
IllegalArgumentException |
if the redirect does not correspond to a valid source
of data, that is, has type
WRITE or
APPEND |
redirectOutput
public ProcessBuilder redirectOutput (ProcessBuilder.Redirect destination)
Sets this process builder's standard output destination.
Subprocesses subsequently started by this object's start()
method send their standard output to this destination.
If the destination is Redirect.PIPE
(the initial value), then the standard output of a subprocess
can be read using the input stream returned by Process.getInputStream()
.
If the destination is set to any other value, then
Process#getInputStream()
will return a
null input stream.
Parameters | |
---|---|
destination |
ProcessBuilder.Redirect : the new standard output destination |
Returns | |
---|---|
ProcessBuilder |
this process builder |
Throws | |
---|---|
IllegalArgumentException |
if the redirect does not correspond to a valid
destination of data, that is, has type
READ |
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 | |
---|---|
ProcessBuilder.Redirect |
this process builder's standard output destination |
redirectOutput
public ProcessBuilder redirectOutput (File file)
Sets this process builder's standard output destination to a file.
This is a convenience method. An invocation of the form
redirectOutput(file)
behaves in exactly the same way as the invocation
redirectOutput
(Redirect.to(file))
.
Parameters | |
---|---|
file |
File : the new standard output destination |
Returns | |
---|---|
ProcessBuilder |
this process builder |
start
public Process start ()
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()
.
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.
A minimal set of system dependent environment variables may
be required to start a process on some operating systems.
As a result, the subprocess may inherit additional environment variable
settings beyond those in the process builder's environment()
.
If there is a security manager, its
checkExec
method is called with the first component of this object's
command
array as its argument. This may result in
a SecurityException
being thrown.
Starting an operating system process is highly system-dependent. Among the many things that can go wrong are:
- The operating system program file was not found.
- Access to the program file was denied.
- The working directory does not exist.
In such cases an exception will be thrown. The exact nature
of the exception is system-dependent, but it will always be a
subclass of IOException
.
Subsequent modifications to this process builder will not
affect the returned Process
.
Returns | |
---|---|
Process |
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
|
IOException |
if an I/O error occurs |
Content and code samples on this page are subject to the licenses described in the Content License. Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
Last updated 2024-02-16 UTC.