ProcessBuilderpublic 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:
- 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 {@link 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 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 {@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. |
| Fields Summary |
|---|
| private List | command | | private File | directory | | private Map | environment | | private boolean | redirectErrorStream |
| Constructors Summary |
|---|
public ProcessBuilder(List 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.
if (command == null)
throw new NullPointerException();
this.command = command;
| 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.
this.command = new ArrayList<String>(command.length);
for (String arg : command)
this.command.add(arg);
|
| Methods Summary |
|---|
| public java.lang.ProcessBuilder | command(java.util.List 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.
if (command == null)
throw new NullPointerException();
this.command = command;
return this;
| | public java.lang.ProcessBuilder | command(java.lang.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.
this.command = new ArrayList<String>(command.length);
for (String arg : command)
this.command.add(arg);
return this;
| | public java.util.List | 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.
return command;
| | public java.io.File | directory()Returns this process builder's working directory.
Subprocesses subsequently started by this object's {@link
#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.
return directory;
| | public java.lang.ProcessBuilder | directory(java.io.File directory)Sets this process builder's working directory.
Subprocesses subsequently started by this object's {@link
#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.
this.directory = directory;
return this;
| | public java.util.Map | 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
{@link System#getenv()}). Subprocesses subsequently started by
this object's {@link #start()} method will use this map as
their 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.
SecurityManager security = System.getSecurityManager();
if (security != null)
security.checkPermission(new RuntimePermission("getenv.*"));
if (environment == null)
environment = ProcessEnvironment.environment();
assert environment != null;
return environment;
| | java.lang.ProcessBuilder | environment(java.lang.String[] envp)
assert environment == null;
if (envp != null) {
environment = ProcessEnvironment.emptyEnvironment(envp.length);
assert environment != null;
for (String envstring : envp) {
// Before 1.5, we blindly passed invalid envstrings
// to the child process.
// We would like to throw an exception, but do not,
// for compatibility with old broken code.
// Silently discard any trailing junk.
if (envstring.indexOf((int) '\u0000") != -1)
envstring = envstring.replaceFirst("\u0000.*", "");
int eqlsign =
envstring.indexOf('=", ProcessEnvironment.MIN_NAME_LENGTH);
// Silently ignore envstrings lacking the required `='.
if (eqlsign != -1)
environment.put(envstring.substring(0,eqlsign),
envstring.substring(eqlsign+1));
}
}
return this;
| | 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
{@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.
return redirectErrorStream;
| | public java.lang.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
{@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.
this.redirectErrorStream = redirectErrorStream;
return this;
| | public java.lang.Process | start()Starts a new process using the attributes of this process builder.
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:
- 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 {@link IOException}.
Subsequent modifications to this process builder will not
affect the returned {@link Process}.
// Must convert to array first -- a malicious user-supplied
// list might try to circumvent the security check.
String[] cmdarray = command.toArray(new String[command.size()]);
for (String arg : cmdarray)
if (arg == null)
throw new NullPointerException();
// Throws IndexOutOfBoundsException if command is empty
String prog = cmdarray[0];
SecurityManager security = System.getSecurityManager();
if (security != null)
security.checkExec(prog);
String dir = directory == null ? null : directory.toString();
try {
return ProcessImpl.start(cmdarray,
environment,
dir,
redirectErrorStream);
} catch (IOException e) {
// It's much easier for us to create a high-quality error
// message than the low-level C code which found the problem.
throw new IOException(
"Cannot run program \"" + prog + "\""
+ (dir == null ? "" : " (in directory \"" + dir + "\")")
+ ": " + e.getMessage(),
e);
}
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