Process
provides control of native processes started by ProcessBuilder.start and Runtime.exec. The class 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
ProcessBuilder.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 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 process 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 I/O streams of characters and lines can be written and read using the methods outputWriter(), outputWriter(Charset)}, inputReader(), inputReader(Charset), errorReader(), and errorReader(Charset). The parent process uses these streams to feed input to and get output from the process. 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 process may cause the process to block, or even deadlock.
Where desired, process I/O can also be redirected using methods of the ProcessBuilder class.
The process is not killed when there are no more references to the Process object, but rather the process continues executing asynchronously.
There is no requirement that the 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, ProcessBuilder.start() is the preferred way to create a Process.
Subclasses of Process should override the onExit() and toHandle() methods to provide a fully functional Process including the process id, information about the process, direct children, and direct children plus descendants of those children of the process. Delegating to the underlying Process or ProcessHandle is typically easiest and most efficient.
Constructors
Default constructor for Process.
Returns a snapshot of the direct children of the process.
Returns a snapshot of the descendants of the process.
abstract void
Kills the process forcibly.
Returns a
BufferedReader
connected to the standard error of the process.
Returns a
BufferedReader
connected to the standard error of this process using a Charset.
abstract int
Returns the exit value for the process.
Returns the input stream connected to the error output of the process.
Returns the input stream connected to the normal output of the process.
Returns the output stream connected to the normal input of the process.
Returns a snapshot of information about the process.
Returns a
BufferedReader
connected to the standard output of the process.
Returns a
BufferedReader
connected to the standard output of this process using a Charset.
boolean
Tests whether the process represented by this Process is alive.
Returns a CompletableFuture<Process> for the termination of the Process.
Returns a BufferedWriter connected to the normal input of the process using the native encoding.
Returns a BufferedWriter connected to the normal input of the process using a Charset.
long
Returns the native process ID of the process.
boolean
Returns
true
if the implementation of
destroy()
is to normally terminate the process, Returns
false
if the implementation of
destroy
forcibly and immediately terminates the process.
Returns a ProcessHandle for the Process.
abstract int
Causes the current thread to wait, if necessary, until the process represented by this Process object has terminated.
boolean
Causes the current thread to wait, if necessary, until the process represented by this Process object has terminated, or the specified waiting time elapses.
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, waitpublic Process()
Default constructor for Process.
Returns the output stream connected to the normal input of the process. Output to the stream is piped into the standard input of the process represented by this
Process
object.
If the standard input of the process has been redirected using ProcessBuilder.redirectInput then this method will return a null output stream.
getOutputStream() and either outputWriter() or outputWriter(Charset), BufferedWriter.flush should be called before writes to the OutputStream.
Returns the input stream connected to the normal output of the process. The stream obtains data piped from the standard output of the process represented by this
Process
object.
If the standard output of the process has been redirected using ProcessBuilder.redirectOutput then this method will return a null input stream.
Otherwise, if the standard error of the process 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 process.
getInputStream() and inputReader() with extreme care. The BufferedReader may have buffered input from the input stream.
getErrorStream() and errorReader() with extreme care. The BufferedReader may have buffered input from the error stream.
Returns a
BufferedReader
connected to the standard output of the process. The
Charset
for the native encoding is used to read characters, lines, or stream lines from standard output.
This method delegates to inputReader(Charset) using the Charset named by the native.encoding system property. If the native.encoding is not a valid charset name or not supported the Charset.defaultCharset() is used.
BufferedReader using the native.encoding if supported, otherwise, the Charset.defaultCharset()
Returns a
BufferedReader
connected to the standard output of this process using a Charset. The
BufferedReader
can be used to read characters, lines, or stream lines of the standard output.
Characters are read by an InputStreamReader that reads and decodes bytes from this process getInputStream(). Bytes are decoded to characters using the charset; malformed-input and unmappable-character sequences are replaced with the charset's default replacement. The BufferedReader reads and buffers characters from the InputStreamReader.
The first call to this method creates the BufferedReader, if called again with the same charset the same BufferedReader is returned. It is an error to call this method again with a different charset.
If the standard output of the process has been redirected using ProcessBuilder.redirectOutput then the InputStreamReader will be reading from a null input stream.
Otherwise, if the standard error of the process has been redirected using ProcessBuilder.redirectErrorStream then the input reader returned by this method will receive the merged standard output and the standard error of the process.
getInputStream() and inputReader(Charset) has unpredictable behavior since the buffered reader reads ahead from the input stream.
When the process has terminated, and the standard input has not been redirected, reading of the bytes available from the underlying stream is on a best effort basis and may be unpredictable.
charset - the Charset used to decode bytes to characters
BufferedReader for the standard output of the process using the charset
NullPointerException - if the charset is null
IllegalStateException - if called more than once with different charset arguments
Returns a
BufferedReader
connected to the standard error of the process. The
Charset
for the native encoding is used to read characters, lines, or stream lines from standard error.
This method delegates to errorReader(Charset) using the Charset named by the native.encoding system property. If the native.encoding is not a valid charset name or not supported the Charset.defaultCharset() is used.
BufferedReader using the native.encoding if supported, otherwise, the Charset.defaultCharset()
Returns a
BufferedReader
connected to the standard error of this process using a Charset. The
BufferedReader
can be used to read characters, lines, or stream lines of the standard error.
Characters are read by an InputStreamReader that reads and decodes bytes from this process getErrorStream(). Bytes are decoded to characters using the charset; malformed-input and unmappable-character sequences are replaced with the charset's default replacement. The BufferedReader reads and buffers characters from the InputStreamReader.
The first call to this method creates the BufferedReader, if called again with the same charset the same BufferedReader is returned. It is an error to call this method again with a different charset.
If the standard error of the process has been redirected using ProcessBuilder.redirectError or ProcessBuilder.redirectErrorStream then the InputStreamReader will be reading from a null input stream.
getErrorStream() and errorReader(Charset) has unpredictable behavior since the buffered reader reads ahead from the error stream.
When the process has terminated, and the standard error has not been redirected, reading of the bytes available from the underlying stream is on a best effort basis and may be unpredictable.
charset - the Charset used to decode bytes to characters
BufferedReader for the standard error of the process using the charset
NullPointerException - if the charset is null
IllegalStateException - if called more than once with different charset arguments
Returns a
BufferedWriter
connected to the normal input of the process using the native encoding. Writes text to a character-output stream, buffering characters so as to provide for the efficient writing of single characters, arrays, and strings.
This method delegates to outputWriter(Charset) using the Charset named by the native.encoding system property. If the native.encoding is not a valid charset name or not supported the Charset.defaultCharset() is used.
BufferedWriter to the standard input of the process using the charset for the native.encoding system property
Returns a
BufferedWriter
connected to the normal input of the process using a Charset. Writes text to a character-output stream, buffering characters so as to provide for the efficient writing of single characters, arrays, and strings.
Characters written by the writer are encoded to bytes using OutputStreamWriter and the Charset are written to the standard input of the process represented by this Process. Malformed-input and unmappable-character sequences are replaced with the charset's default replacement.
The first call to this method creates the BufferedWriter, if called again with the same charset the same BufferedWriter is returned. It is an error to call this method again with a different charset.
If the standard input of the process has been redirected using ProcessBuilder.redirectInput then the OutputStreamWriter writes to a null output stream.
BufferedWriter with a PrintWriter provides efficient buffering and formatting of primitives and objects as well as support for auto-flush on line endings. Call the BufferedWriter.flush() method to flush buffered output to the process.
When writing to both getOutputStream() and either outputWriter() or outputWriter(Charset), BufferedWriter.flush should be called before writes to the OutputStream.
charset - the Charset to encode characters to bytes
BufferedWriter to the standard input of the process using the charset
NullPointerException - if the charset is null
IllegalStateException - if called more than once with different charset arguments
Causes the current thread to wait, if necessary, until the process represented by this Process object has terminated. This method returns immediately if the process has already terminated. If the process has not yet terminated, the calling thread will be blocked until the process exits.
Process object. By convention, the value 0 indicates normal termination.
InterruptedException - if the current thread is interrupted by another thread while it is waiting, then the wait is ended and an InterruptedException is thrown.
Causes the current thread to wait, if necessary, until the process represented by this
Process
object has terminated, or the specified waiting time elapses.
If the process 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 method 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.
timeout - the maximum time to wait
unit - the time unit of the timeout argument
true if the process has exited and false if the waiting time elapsed before the process has exited.
InterruptedException - if the current thread is interrupted while waiting.
NullPointerException - if unit is null
public abstract int exitValue()
Returns the exit value for the process.
Process object. By convention, the value 0 indicates normal termination.
IllegalThreadStateException - if the process represented by this Process object has not yet terminated
public abstract void destroy()
Kills the process. Whether the process represented by this
Process
object is
normally terminatedor not is implementation dependent. Forcible process destruction is defined as the immediate termination of a process, whereas normal termination allows the process to shut down cleanly. If the process is not alive, no action is taken.
The CompletableFuture from onExit() is completed when the process has terminated.
Kills the process forcibly. The process represented by this
Process
object is forcibly terminated. Forcible process destruction is defined as the immediate termination of a process, whereas normal termination allows the process to shut down cleanly. If the process is not alive, no action is taken.
The CompletableFuture from onExit() is completed when the process has terminated.
Invoking this method on Process objects returned by ProcessBuilder.start() and Runtime.exec(java.lang.String) forcibly terminate the process.
isAlive() may return true for a brief period after destroyForcibly() is called. This method may be chained to waitFor() if needed.
destroy() and so may not forcibly terminate the process.
Process object representing the process forcibly destroyed
public boolean supportsNormalTermination()
Returns
true
if the implementation of
destroy()
is to normally terminate the process, Returns
false
if the implementation of
destroy
forcibly and immediately terminates the process.
Invoking this method on Process objects returned by ProcessBuilder.start() and Runtime.exec(java.lang.String) return true or false depending on the platform implementation.
UnsupportedOperationException and performs no other action.
true if the implementation of destroy() is to normally terminate the process; otherwise, destroy() forcibly terminates the process
UnsupportedOperationException - if the Process implementation does not support this operation
public boolean isAlive()
Tests whether the process represented by this Process is alive.
true if the process represented by this Process object has not yet terminated.
public long pid()
Returns the native process ID of the process. The native process ID is an identification number that the operating system assigns to the process.
toHandle().pid().
UnsupportedOperationException - if the Process implementation does not support this operation
Returns a
CompletableFuture<Process>
for the termination of the Process. The
CompletableFuture
provides the ability to trigger dependent functions or actions that may be run synchronously or asynchronously upon process termination. When the process has terminated the CompletableFuture is
completed
regardless of the exit status of the process.
Calling onExit().get() waits for the process to terminate and returns the Process. The future can be used to check if the process is done or to wait for it to terminate. Cancelling the CompletableFuture does not affect the Process.
Processes returned from ProcessBuilder.start() override the default implementation to provide an efficient mechanism to wait for process exit.
onExit is an alternative to waitFor that enables both additional concurrency and convenient access to the result of the Process. Lambda expressions can be used to evaluate the result of the Process execution. If there is other processing to be done before the value is used then onExit is a convenient mechanism to free the current thread and block only if and when the value is needed.
Process p = new ProcessBuilder("cmp", "f1", "f2").start();
Future<Boolean> identical = p.onExit().thenApply(p1 -> p1.exitValue() == 0);
...
if (identical.get()) { ... }
, The process may be observed to have terminated with isAlive() before the ComputableFuture is completed and dependent actions are invoked.
waitFor() in a separate thread repeatedly until it returns successfully. If the execution of waitFor is interrupted, the thread's interrupt status is preserved.
When waitFor() returns successfully the CompletableFuture is completed regardless of the exit status of the process. This implementation may consume a lot of memory for thread stacks if a large number of processes are waited for concurrently.
External implementations should override this method and provide a more efficient implementation. For example, to delegate to the underlying process, it can do the following:
public CompletableFuture<Process> onExit() {
return delegate.onExit().thenApply(p -> this);
}
CompletableFuture<Process> for the Process
UnsupportedOperationException and performs no other action. Subclasses should override this method to provide a ProcessHandle for the process. The methods pid(), info(), children(), and descendants(), unless overridden, operate on the ProcessHandle.
UnsupportedOperationException - if the Process implementation does not support this operation
SecurityException - if a security manager has been installed and it denies RuntimePermission("manageProcess")
A ProcessHandle.Info instance has accessor methods that return information about the process if it is available.
toHandle().info().
UnsupportedOperationException - if the Process implementation does not support this operation
Returns a snapshot of the direct children of the process. The parent of a direct child process is the process. Typically, a process that is
not alivehas no children.
Note that processes are created and terminate asynchronously. There is no guarantee that a process is alive.
toHandle().children().
UnsupportedOperationException - if the Process implementation does not support this operation
SecurityException - if a security manager has been installed and it denies RuntimePermission("manageProcess")
Returns a snapshot of the descendants of the process. The descendants of a process are the children of the process plus the descendants of those children, recursively. Typically, a process that is
not alivehas no children.
Note that processes are created and terminate asynchronously. There is no guarantee that a process is alive.
toHandle().descendants().
UnsupportedOperationException - if the Process implementation does not support this operation
SecurityException - if a security manager has been installed and it denies RuntimePermission("manageProcess")
RetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4