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.

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(java.lang.Object) 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.

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.

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.

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.

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)).

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)).

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)).

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)

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.

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.

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.