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Process

public abstract class Process
extends Object

java.lang.Object
   ↳ java.lang.Process


The start() and Runtime.exec methods create a native process and return an instance of a subclass of Process that can be used to control the process and obtain information about it. The class Process provides methods for performing input from the process, performing output to the process, waiting for the process to complete, checking the exit status of the process, and destroying (killing) the process.

The methods that create processes may not work well for special processes on certain native platforms, such as native windowing processes, daemon processes, Win16/DOS processes on Microsoft Windows, or shell scripts.

By default, the created subprocess does not have its own terminal or console. All its standard I/O (i.e. stdin, stdout, stderr) operations will be redirected to the parent process, where they can be accessed via the streams obtained using the methods getOutputStream(), getInputStream(), and getErrorStream(). The parent process uses these streams to feed input to and get output from the subprocess. Because some native platforms only provide limited buffer size for standard input and output streams, failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, or even deadlock.

Where desired, subprocess I/O can also be redirected using methods of the ProcessBuilder class.

The subprocess is not killed when there are no more references to the Process object, but rather the subprocess continues executing asynchronously.

There is no requirement that a process represented by a Process object execute asynchronously or concurrently with respect to the Java process that owns the Process object.

As of 1.5, start() is the preferred way to create a Process.

Summary

Public constructors

Process()

Public methods

abstract void destroy()

Kills the subprocess.

Process destroyForcibly()

Kills the subprocess.

abstract int exitValue()

Returns the exit value for the subprocess.

abstract InputStream getErrorStream()

Returns the input stream connected to the error output of the subprocess.

abstract InputStream getInputStream()

Returns the input stream connected to the normal output of the subprocess.

abstract OutputStream getOutputStream()

Returns the output stream connected to the normal input of the subprocess.

boolean isAlive()

Tests whether the subprocess represented by this Process is alive.

abstract int waitFor()

Causes the current thread to wait, if necessary, until the process represented by this Process object has terminated.

boolean waitFor(long timeout, TimeUnit unit)

Causes the current thread to wait, if necessary, until the subprocess represented by this Process object has terminated, or the specified waiting time elapses.

Inherited methods

From class java.lang.Object

Public constructors

Process

added in API level 1
Process ()

Public methods

destroy

added in API level 1
void destroy ()

Kills the subprocess. Whether the subprocess represented by this Process object is forcibly terminated or not is implementation dependent.

destroyForcibly

added in API level 26
Process destroyForcibly ()

Kills the subprocess. The subprocess represented by this Process object is forcibly terminated.

The default implementation of this method invokes destroy() and so may not forcibly terminate the process. Concrete implementations of this class are strongly encouraged to override this method with a compliant implementation. Invoking this method on Process objects returned by start() and exec(String) will forcibly terminate the process.

Note: The subprocess may not terminate immediately. i.e. isAlive() may return true for a brief period after destroyForcibly() is called. This method may be chained to waitFor() if needed.

Returns
Process the Process object representing the subprocess to be forcibly destroyed.

exitValue

added in API level 1
int exitValue ()

Returns the exit value for the subprocess.

Returns
int the exit value of the subprocess represented by this Process object. By convention, the value 0 indicates normal termination.

Throws
IllegalThreadStateException if the subprocess represented by this Process object has not yet terminated

getErrorStream

added in API level 1
InputStream getErrorStream ()

Returns the input stream connected to the error output of the subprocess. The stream obtains data piped from the error output of the process represented by this Process object.

If the standard error of the subprocess has been redirected using ProcessBuilder.redirectError or ProcessBuilder.redirectErrorStream then this method will return a null input stream.

Implementation note: It is a good idea for the returned input stream to be buffered.

Returns
InputStream the input stream connected to the error output of the subprocess

getInputStream

added in API level 1
InputStream getInputStream ()

Returns the input stream connected to the normal output of the subprocess. The stream obtains data piped from the standard output of the process represented by this Process object.

If the standard output of the subprocess has been redirected using ProcessBuilder.redirectOutput then this method will return a null input stream.

Otherwise, if the standard error of the subprocess has been redirected using ProcessBuilder.redirectErrorStream then the input stream returned by this method will receive the merged standard output and the standard error of the subprocess.

Implementation note: It is a good idea for the returned input stream to be buffered.

Returns
InputStream the input stream connected to the normal output of the subprocess

getOutputStream

added in API level 1
OutputStream getOutputStream ()

Returns the output stream connected to the normal input of the subprocess. Output to the stream is piped into the standard input of the process represented by this Process object.

If the standard input of the subprocess has been redirected using ProcessBuilder.redirectInput then this method will return a null output stream.

Implementation note: It is a good idea for the returned output stream to be buffered.

Returns
OutputStream the output stream connected to the normal input of the subprocess

isAlive

added in API level 26
boolean isAlive ()

Tests whether the subprocess represented by this Process is alive.

Returns
boolean true if the subprocess represented by this Process object has not yet terminated.

waitFor

added in API level 1
int waitFor ()

Causes the current thread to wait, if necessary, until the process represented by this Process object has terminated. This method returns immediately if the subprocess has already terminated. If the subprocess has not yet terminated, the calling thread will be blocked until the subprocess exits.

Returns
int the exit value of the subprocess represented by this Process object. By convention, the value 0 indicates normal termination.

Throws
InterruptedException if the current thread is interrupted by another thread while it is waiting, then the wait is ended and an InterruptedException is thrown.

waitFor

added in API level 26
boolean waitFor (long timeout, 
                TimeUnit unit)

Causes the current thread to wait, if necessary, until the subprocess represented by this Process object has terminated, or the specified waiting time elapses.

If the subprocess has already terminated then this method returns immediately with the value true. If the process has not terminated and the timeout value is less than, or equal to, zero, then this method returns immediately with the value false.

The default implementation of this methods polls the exitValue to check if the process has terminated. Concrete implementations of this class are strongly encouraged to override this method with a more efficient implementation.

Parameters
timeout long: the maximum time to wait

unit TimeUnit: the time unit of the timeout argument

Returns
boolean true if the subprocess has exited and false if the waiting time elapsed before the subprocess has exited.

Throws
InterruptedException if the current thread is interrupted while waiting.
NullPointerException if unit is null
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