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public final class ProcessBuilder extends Object
This class is used to create operating system processes.
Each ProcessBuilder
instance manages a collection
of process attributes. The {@link #start()} method creates a new
{@link Process} instance with those attributes. The {@link
#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:
user.dir
.
false
, meaning that the standard output and error
output of a subprocess are sent to two separate streams, which can
be accessed using the {@link Process#getInputStream()} and {@link
Process#getErrorStream()} methods. If the value is set to
true
, the standard error is merged with the standard
output. This makes it easier to correlate error messages with the
corresponding output. In this case, the merged data can be read
from the stream returned by {@link Process#getInputStream()}, while
reading from the stream returned by {@link
Process#getErrorStream()} will get an immediate end of file.
Modifying a process builder's attributes will affect processes subsequently started by that object's {@link #start()} method, but will never affect previously started processes or the Java process itself.
Most error checking is performed by the {@link #start()} method. It is possible to modify the state of an object so that {@link #start()} will fail. For example, setting the command attribute to an empty list will not throw an exception unless {@link #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:
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")); Process p = pb.start();
To start a process with an explicit set of environment variables, first call {@link java.util.Map#clear() Map.clear()} before adding environment variables.
Constructor Summary | |
---|---|
ProcessBuilder(List 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. |
Method Summary | |
---|---|
List |
command() Returns this process builder's operating system program and arguments. |
ProcessBuilder |
Sets this process builder's operating system program and arguments. |
ProcessBuilder |
Sets this process builder's operating system program and arguments. |
File |
Returns this process builder's working directory. |
ProcessBuilder |
Sets this process builder's working directory. |
Map |
Returns a string map view of this process builder's environment. |
boolean |
Tells whether this process builder merges standard error and standard output. |
ProcessBuilder |
redirectErrorStream(boolean redirectErrorStream) Sets this process builder's redirectErrorStream property.
|
Process |
start() Starts a new process using the attributes of this process builder. |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
---|
public ProcessBuilder(List command)
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.
command
- The list containing the program and its argumentspublic ProcessBuilder(String[] command)
command
array, in the same order. It is not checked whether
command
corresponds to a valid operating system
command.
command
- A string array containing the program and its argumentsMethod Detail |
---|
public List command()
public ProcessBuilder command(List command)
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.
command
- The list containing the program and its argumentspublic ProcessBuilder command(String[] command)
command
array, in the same order. It is not
checked whether command
corresponds to a valid
operating system command.
command
- A string array containing the program and its argumentspublic File directory()
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.
public ProcessBuilder directory(File directory)
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.
directory
- The new working directorypublic Map environment()
The returned object may be modified using ordinary {@link
java.util.Map Map} operations. These modifications will be
visible to subprocesses started via the {@link #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
{@link System#getenv 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 {@link NullPointerException}. Attempting to query the presence of a key or value which is not of type {@link String} will throw a {@link 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 {@link UnsupportedOperationException} or {@link 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 {@link Object#equals} and {@link Object#hashCode} methods.
The returned map is typically case-sensitive on all platforms.
If a security manager exists, its
{@link SecurityManager#checkPermission checkPermission}
method is called with a
{@link RuntimePermission}("getenv.*")
permission. This may result in a {@link SecurityException} being
thrown.
When passing information to a Java subprocess, system properties are generally preferred over environment variables.
public boolean redirectErrorStream()
If this property is true
, then any error output
generated by subprocesses subsequently started by this object's
{@link #start()} method will be merged with the standard
output, so that both can be read using the
{@link Process#getInputStream()} method. This makes it easier
to correlate error messages with the corresponding output.
The initial value is false
.
redirectErrorStream
propertypublic ProcessBuilder redirectErrorStream(boolean redirectErrorStream)
redirectErrorStream
property.
If this property is true
, then any error output
generated by subprocesses subsequently started by this object's
{@link #start()} method will be merged with the standard
output, so that both can be read using the
{@link Process#getInputStream()} method. This makes it easier
to correlate error messages with the corresponding output.
The initial value is false
.
redirectErrorStream
- The new property valuepublic Process start() throws IOException
The new process will invoke the command and arguments given by {@link #command()}, in a working directory as given by {@link #directory()}, with a process environment as given by {@link #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
{@link SecurityManager#checkExec checkExec}
method is called with the first component of this object's
command
array as its argument. This may result in
a {@link SecurityException} being thrown.
Starting an operating system process is highly system-dependent. Among the many things that can go wrong are:
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 {@link IOException}.
Subsequent modifications to this process builder will not affect the returned {@link Process}.
IOException
- If an I/O error occurs
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