JDK8/Java8源码在线阅读
/*
* Copyright (c) 2007, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.nio.channels;
import java.nio.file.*;
import java.nio.file.attribute.FileAttribute;
import java.nio.file.spi.*;
import java.nio.ByteBuffer;
import java.io.IOException;
import java.util.concurrent.Future;
import java.util.concurrent.ExecutorService;
import java.util.Set;
import java.util.HashSet;
import java.util.Collections;
/**
* An asynchronous channel for reading, writing, and manipulating a file.
*
* <p> An asynchronous file channel is created when a file is opened by invoking
* one of the {@link #open open} methods defined by this class. The file contains
* a variable-length sequence of bytes that can be read and written and whose
* current size can be {@link #size() queried}. The size of the file increases
* when bytes are written beyond its current size; the size of the file decreases
* when it is {@link #truncate truncated}.
*
* <p> An asynchronous file channel does not have a <i>current position</i>
* within the file. Instead, the file position is specified to each read and
* write method that initiates asynchronous operations. A {@link CompletionHandler}
* is specified as a parameter and is invoked to consume the result of the I/O
* operation. This class also defines read and write methods that initiate
* asynchronous operations, returning a {@link Future} to represent the pending
* result of the operation. The {@code Future} may be used to check if the
* operation has completed, wait for its completion, and retrieve the result.
*
* <p> In addition to read and write operations, this class defines the
* following operations: </p>
*
* <ul>
*
* <li><p> Updates made to a file may be {@link #force <i>forced
* out</i>} to the underlying storage device, ensuring that data are not
* lost in the event of a system crash. </p></li>
*
* <li><p> A region of a file may be {@link #lock <i>locked</i>} against
* access by other programs. </p></li>
*
* </ul>
*
* <p> An {@code AsynchronousFileChannel} is associated with a thread pool to
* which tasks are submitted to handle I/O events and dispatch to completion
* handlers that consume the results of I/O operations on the channel. The
* completion handler for an I/O operation initiated on a channel is guaranteed
* to be invoked by one of the threads in the thread pool (This ensures that the
* completion handler is run by a thread with the expected <em>identity</em>).
* Where an I/O operation completes immediately, and the initiating thread is
* itself a thread in the thread pool, then the completion handler may be invoked
* directly by the initiating thread. When an {@code AsynchronousFileChannel} is
* created without specifying a thread pool then the channel is associated with
* a system-dependent default thread pool that may be shared with other
* channels. The default thread pool is configured by the system properties
* defined by the {@link AsynchronousChannelGroup} class.
*
* <p> Channels of this type are safe for use by multiple concurrent threads. The
* {@link Channel#close close} method may be invoked at any time, as specified
* by the {@link Channel} interface. This causes all outstanding asynchronous
* operations on the channel to complete with the exception {@link
* AsynchronousCloseException}. Multiple read and write operations may be
* outstanding at the same time. When multiple read and write operations are
* outstanding then the ordering of the I/O operations, and the order that the
* completion handlers are invoked, is not specified; they are not, in particular,
* guaranteed to execute in the order that the operations were initiated. The
* {@link java.nio.ByteBuffer ByteBuffers} used when reading or writing are not
* safe for use by multiple concurrent I/O operations. Furthermore, after an I/O
* operation is initiated then care should be taken to ensure that the buffer is
* not accessed until after the operation has completed.
*
* <p> As with {@link FileChannel}, the view of a file provided by an instance of
* this class is guaranteed to be consistent with other views of the same file
* provided by other instances in the same program. The view provided by an
* instance of this class may or may not, however, be consistent with the views
* seen by other concurrently-running programs due to caching performed by the
* underlying operating system and delays induced by network-filesystem protocols.
* This is true regardless of the language in which these other programs are
* written, and whether they are running on the same machine or on some other
* machine. The exact nature of any such inconsistencies are system-dependent
* and are therefore unspecified.
*
* @since 1.7
*/
public abstract class AsynchronousFileChannel
implements AsynchronousChannel
{
/**
* Initializes a new instance of this class.
*/
protected AsynchronousFileChannel() {
}
/**
* Opens or creates a file for reading and/or writing, returning an
* asynchronous file channel to access the file.
*
* <p> The {@code options} parameter determines how the file is opened.
* The {@link StandardOpenOption#READ READ} and {@link StandardOpenOption#WRITE
* WRITE} options determines if the file should be opened for reading and/or
* writing. If neither option is contained in the array then an existing file
* is opened for reading.
*
* <p> In addition to {@code READ} and {@code WRITE}, the following options
* may be present:
*
* <table border=1 cellpadding=5 summary="">
* <tr> <th>Option</th> <th>Description</th> </tr>
* <tr>
* <td> {@link StandardOpenOption#TRUNCATE_EXISTING TRUNCATE_EXISTING} </td>
* <td> When opening an existing file, the file is first truncated to a
* size of 0 bytes. This option is ignored when the file is opened only
* for reading.</td>
* </tr>
* <tr>
* <td> {@link StandardOpenOption#CREATE_NEW CREATE_NEW} </td>
* <td> If this option is present then a new file is created, failing if
* the file already exists. When creating a file the check for the
* existence of the file and the creation of the file if it does not exist
* is atomic with respect to other file system operations. This option is
* ignored when the file is opened only for reading. </td>
* </tr>
* <tr>
* <td > {@link StandardOpenOption#CREATE CREATE} </td>
* <td> If this option is present then an existing file is opened if it
* exists, otherwise a new file is created. When creating a file the check
* for the existence of the file and the creation of the file if it does
* not exist is atomic with respect to other file system operations. This
* option is ignored if the {@code CREATE_NEW} option is also present or
* the file is opened only for reading. </td>
* </tr>
* <tr>
* <td > {@link StandardOpenOption#DELETE_ON_CLOSE DELETE_ON_CLOSE} </td>
* <td> When this option is present then the implementation makes a
* <em>best effort</em> attempt to delete the file when closed by the
* the {@link #close close} method. If the {@code close} method is not
* invoked then a <em>best effort</em> attempt is made to delete the file
* when the Java virtual machine terminates. </td>
* </tr>
* <tr>
* <td>{@link StandardOpenOption#SPARSE SPARSE} </td>
* <td> When creating a new file this option is a <em>hint</em> that the
* new file will be sparse. This option is ignored when not creating
* a new file. </td>
* </tr>
* <tr>
* <td> {@link StandardOpenOption#SYNC SYNC} </td>
* <td> Requires that every update to the file's content or metadata be
* written synchronously to the underlying storage device. (see <a
* href="../file/package-summary.html#integrity"> Synchronized I/O file
* integrity</a>). </td>
* </tr>
* <tr>
* <td> {@link StandardOpenOption#DSYNC DSYNC} </td>
* <td> Requires that every update to the file's content be written
* synchronously to the underlying storage device. (see <a
* href="../file/package-summary.html#integrity"> Synchronized I/O file
* integrity</a>). </td>
* </tr>
* </table>
*
* <p> An implementation may also support additional options.
*
* <p> The {@code executor} parameter is the {@link ExecutorService} to
* which tasks are submitted to handle I/O events and dispatch completion
* results for operations initiated on resulting channel.
* The nature of these tasks is highly implementation specific and so care
* should be taken when configuring the {@code Executor}. Minimally it
* should support an unbounded work queue and should not run tasks on the
* caller thread of the {@link ExecutorService#execute execute} method.
* Shutting down the executor service while the channel is open results in
* unspecified behavior.
*
* <p> The {@code attrs} parameter is an optional array of file {@link
* FileAttribute file-attributes} to set atomically when creating the file.
*
* <p> The new channel is created by invoking the {@link
* FileSystemProvider#newFileChannel newFileChannel} method on the
* provider that created the {@code Path}.
*
* @param file
* The path of the file to open or create
* @param options
* Options specifying how the file is opened
* @param executor
* The thread pool or {@code null} to associate the channel with
* the default thread pool
* @param attrs
* An optional list of file attributes to set atomically when
* creating the file
*
* @return A new asynchronous file channel
*
* @throws IllegalArgumentException
* If the set contains an invalid combination of options
* @throws UnsupportedOperationException
* If the {@code file} is associated with a provider that does not
* support creating asynchronous file channels, or an unsupported
* open option is specified, or the array contains an attribute that
* cannot be set atomically when creating the file
* @throws IOException
* If an I/O error occurs
* @throws SecurityException
* If a security manager is installed and it denies an
* unspecified permission required by the implementation.
* In the case of the default provider, the {@link
* SecurityManager#checkRead(String)} method is invoked to check
* read access if the file is opened for reading. The {@link
* SecurityManager#checkWrite(String)} method is invoked to check
* write access if the file is opened for writing
*/
public static AsynchronousFileChannel open(Path file,
Set<? extends OpenOption> options,
ExecutorService executor,
FileAttribute<?>... attrs)
throws IOException
{
FileSystemProvider provider = file.getFileSystem().provider();
return provider.newAsynchronousFileChannel(file, options, executor, attrs);
}
@SuppressWarnings({"unchecked", "rawtypes"}) // generic array construction
private static final FileAttribute<?>[] NO_ATTRIBUTES = new FileAttribute[0];
/**
* Opens or creates a file for reading and/or writing, returning an
* asynchronous file channel to access the file.
*
* <p> An invocation of this method behaves in exactly the same way as the
* invocation
* <pre>
* ch.{@link #open(Path,Set,ExecutorService,FileAttribute[])
* open}(file, opts, null, new FileAttribute<?>[0]);
* </pre>
* where {@code opts} is a {@code Set} containing the options specified to
* this method.
*
* <p> The resulting channel is associated with default thread pool to which
* tasks are submitted to handle I/O events and dispatch to completion
* handlers that consume the result of asynchronous operations performed on
* the resulting channel.
*
* @param file
* The path of the file to open or create
* @param options
* Options specifying how the file is opened
*
* @return A new asynchronous file channel
*
* @throws IllegalArgumentException
* If the set contains an invalid combination of options
* @throws UnsupportedOperationException
* If the {@code file} is associated with a provider that does not
* support creating file channels, or an unsupported open option is
* specified
* @throws IOException
* If an I/O error occurs
* @throws SecurityException
* If a security manager is installed and it denies an
* unspecified permission required by the implementation.
* In the case of the default provider, the {@link
* SecurityManager#checkRead(String)} method is invoked to check
* read access if the file is opened for reading. The {@link
* SecurityManager#checkWrite(String)} method is invoked to check
* write access if the file is opened for writing
*/
public static AsynchronousFileChannel open(Path file, OpenOption... options)
throws IOException
{
Set<OpenOption> set = new HashSet<OpenOption>(options.length);
Collections.addAll(set, options);
return open(file, set, null, NO_ATTRIBUTES);
}
/**
* Returns the current size of this channel's file.
*
* @return The current size of this channel's file, measured in bytes
*
* @throws ClosedChannelException
* If this channel is closed
* @throws IOException
* If some other I/O error occurs
*/
public abstract long size() throws IOException;
/**
* Truncates this channel's file to the given size.
*
* <p> If the given size is less than the file's current size then the file
* is truncated, discarding any bytes beyond the new end of the file. If
* the given size is greater than or equal to the file's current size then
* the file is not modified. </p>
*
* @param size
* The new size, a non-negative byte count
*
* @return This file channel
*
* @throws NonWritableChannelException
* If this channel was not opened for writing
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws IllegalArgumentException
* If the new size is negative
*
* @throws IOException
* If some other I/O error occurs
*/
public abstract AsynchronousFileChannel truncate(long size) throws IOException;
/**
* Forces any updates to this channel's file to be written to the storage
* device that contains it.
*
* <p> If this channel's file resides on a local storage device then when
* this method returns it is guaranteed that all changes made to the file
* since this channel was created, or since this method was last invoked,
* will have been written to that device. This is useful for ensuring that
* critical information is not lost in the event of a system crash.
*
* <p> If the file does not reside on a local device then no such guarantee
* is made.
*
* <p> The {@code metaData} parameter can be used to limit the number of
* I/O operations that this method is required to perform. Passing
* {@code false} for this parameter indicates that only updates to the
* file's content need be written to storage; passing {@code true}
* indicates that updates to both the file's content and metadata must be
* written, which generally requires at least one more I/O operation.
* Whether this parameter actually has any effect is dependent upon the
* underlying operating system and is therefore unspecified.
*
* <p> Invoking this method may cause an I/O operation to occur even if the
* channel was only opened for reading. Some operating systems, for
* example, maintain a last-access time as part of a file's metadata, and
* this time is updated whenever the file is read. Whether or not this is
* actually done is system-dependent and is therefore unspecified.
*
* <p> This method is only guaranteed to force changes that were made to
* this channel's file via the methods defined in this class.
*
* @param metaData
* If {@code true} then this method is required to force changes
* to both the file's content and metadata to be written to
* storage; otherwise, it need only force content changes to be
* written
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws IOException
* If some other I/O error occurs
*/
public abstract void force(boolean metaData) throws IOException;
/**
* Acquires a lock on the given region of this channel's file.
*
* <p> This method initiates an operation to acquire a lock on the given
* region of this channel's file. The {@code handler} parameter is a
* completion handler that is invoked when the lock is acquired (or the
* operation fails). The result passed to the completion handler is the
* resulting {@code FileLock}.
*
* <p> The region specified by the {@code position} and {@code size}
* parameters need not be contained within, or even overlap, the actual
* underlying file. Lock regions are fixed in size; if a locked region
* initially contains the end of the file and the file grows beyond the
* region then the new portion of the file will not be covered by the lock.
* If a file is expected to grow in size and a lock on the entire file is
* required then a region starting at zero, and no smaller than the
* expected maximum size of the file, should be locked. The two-argument
* {@link #lock(Object,CompletionHandler)} method simply locks a region
* of size {@link Long#MAX_VALUE}. If a lock that overlaps the requested
* region is already held by this Java virtual machine, or this method has
* been invoked to lock an overlapping region and that operation has not
* completed, then this method throws {@link OverlappingFileLockException}.
*
* <p> Some operating systems do not support a mechanism to acquire a file
* lock in an asynchronous manner. Consequently an implementation may
* acquire the file lock in a background thread or from a task executed by
* a thread in the associated thread pool. If there are many lock operations
* outstanding then it may consume threads in the Java virtual machine for
* indefinite periods.
*
* <p> Some operating systems do not support shared locks, in which case a
* request for a shared lock is automatically converted into a request for
* an exclusive lock. Whether the newly-acquired lock is shared or
* exclusive may be tested by invoking the resulting lock object's {@link
* FileLock#isShared() isShared} method.
*
* <p> File locks are held on behalf of the entire Java virtual machine.
* They are not suitable for controlling access to a file by multiple
* threads within the same virtual machine.
*
* @param <A>
* The type of the attachment
* @param position
* The position at which the locked region is to start; must be
* non-negative
* @param size
* The size of the locked region; must be non-negative, and the sum
* {@code position} + {@code size} must be non-negative
* @param shared
* {@code true} to request a shared lock, in which case this
* channel must be open for reading (and possibly writing);
* {@code false} to request an exclusive lock, in which case this
* channel must be open for writing (and possibly reading)
* @param attachment
* The object to attach to the I/O operation; can be {@code null}
* @param handler
* The handler for consuming the result
*
* @throws OverlappingFileLockException
* If a lock that overlaps the requested region is already held by
* this Java virtual machine, or there is already a pending attempt
* to lock an overlapping region
* @throws IllegalArgumentException
* If the preconditions on the parameters do not hold
* @throws NonReadableChannelException
* If {@code shared} is true but this channel was not opened for reading
* @throws NonWritableChannelException
* If {@code shared} is false but this channel was not opened for writing
*/
public abstract <A> void lock(long position,
long size,
boolean shared,
A attachment,
CompletionHandler<FileLock,? super A> handler);
/**
* Acquires an exclusive lock on this channel's file.
*
* <p> This method initiates an operation to acquire a lock on the given
* region of this channel's file. The {@code handler} parameter is a
* completion handler that is invoked when the lock is acquired (or the
* operation fails). The result passed to the completion handler is the
* resulting {@code FileLock}.
*
* <p> An invocation of this method of the form {@code ch.lock(att,handler)}
* behaves in exactly the same way as the invocation
* <pre>
* ch.{@link #lock(long,long,boolean,Object,CompletionHandler) lock}(0L, Long.MAX_VALUE, false, att, handler)
* </pre>
*
* @param <A>
* The type of the attachment
* @param attachment
* The object to attach to the I/O operation; can be {@code null}
* @param handler
* The handler for consuming the result
*
* @throws OverlappingFileLockException
* If a lock is already held by this Java virtual machine, or there
* is already a pending attempt to lock a region
* @throws NonWritableChannelException
* If this channel was not opened for writing
*/
public final <A> void lock(A attachment,
CompletionHandler<FileLock,? super A> handler)
{
lock(0L, Long.MAX_VALUE, false, attachment, handler);
}
/**
* Acquires a lock on the given region of this channel's file.
*
* <p> This method initiates an operation to acquire a lock on the given
* region of this channel's file. The method behaves in exactly the same
* manner as the {@link #lock(long, long, boolean, Object, CompletionHandler)}
* method except that instead of specifying a completion handler, this
* method returns a {@code Future} representing the pending result. The
* {@code Future}'s {@link Future#get() get} method returns the {@link
* FileLock} on successful completion.
*
* @param position
* The position at which the locked region is to start; must be
* non-negative
* @param size
* The size of the locked region; must be non-negative, and the sum
* {@code position} + {@code size} must be non-negative
* @param shared
* {@code true} to request a shared lock, in which case this
* channel must be open for reading (and possibly writing);
* {@code false} to request an exclusive lock, in which case this
* channel must be open for writing (and possibly reading)
*
* @return a {@code Future} object representing the pending result
*
* @throws OverlappingFileLockException
* If a lock is already held by this Java virtual machine, or there
* is already a pending attempt to lock a region
* @throws IllegalArgumentException
* If the preconditions on the parameters do not hold
* @throws NonReadableChannelException
* If {@code shared} is true but this channel was not opened for reading
* @throws NonWritableChannelException
* If {@code shared} is false but this channel was not opened for writing
*/
public abstract Future<FileLock> lock(long position, long size, boolean shared);
/**
* Acquires an exclusive lock on this channel's file.
*
* <p> This method initiates an operation to acquire an exclusive lock on this
* channel's file. The method returns a {@code Future} representing the
* pending result of the operation. The {@code Future}'s {@link Future#get()
* get} method returns the {@link FileLock} on successful completion.
*
* <p> An invocation of this method behaves in exactly the same way as the
* invocation
* <pre>
* ch.{@link #lock(long,long,boolean) lock}(0L, Long.MAX_VALUE, false)
* </pre>
*
* @return a {@code Future} object representing the pending result
*
* @throws OverlappingFileLockException
* If a lock is already held by this Java virtual machine, or there
* is already a pending attempt to lock a region
* @throws NonWritableChannelException
* If this channel was not opened for writing
*/
public final Future<FileLock> lock() {
return lock(0L, Long.MAX_VALUE, false);
}
/**
* Attempts to acquire a lock on the given region of this channel's file.
*
* <p> This method does not block. An invocation always returns immediately,
* either having acquired a lock on the requested region or having failed to
* do so. If it fails to acquire a lock because an overlapping lock is held
* by another program then it returns {@code null}. If it fails to acquire
* a lock for any other reason then an appropriate exception is thrown.
*
* @param position
* The position at which the locked region is to start; must be
* non-negative
*
* @param size
* The size of the locked region; must be non-negative, and the sum
* {@code position} + {@code size} must be non-negative
*
* @param shared
* {@code true} to request a shared lock,
* {@code false} to request an exclusive lock
*
* @return A lock object representing the newly-acquired lock,
* or {@code null} if the lock could not be acquired
* because another program holds an overlapping lock
*
* @throws IllegalArgumentException
* If the preconditions on the parameters do not hold
* @throws ClosedChannelException
* If this channel is closed
* @throws OverlappingFileLockException
* If a lock that overlaps the requested region is already held by
* this Java virtual machine, or if another thread is already
* blocked in this method and is attempting to lock an overlapping
* region of the same file
* @throws NonReadableChannelException
* If {@code shared} is true but this channel was not opened for reading
* @throws NonWritableChannelException
* If {@code shared} is false but this channel was not opened for writing
*
* @throws IOException
* If some other I/O error occurs
*
* @see #lock(Object,CompletionHandler)
* @see #lock(long,long,boolean,Object,CompletionHandler)
* @see #tryLock()
*/
public abstract FileLock tryLock(long position, long size, boolean shared)
throws IOException;
/**
* Attempts to acquire an exclusive lock on this channel's file.
*
* <p> An invocation of this method of the form {@code ch.tryLock()}
* behaves in exactly the same way as the invocation
*
* <pre>
* ch.{@link #tryLock(long,long,boolean) tryLock}(0L, Long.MAX_VALUE, false) </pre>
*
* @return A lock object representing the newly-acquired lock,
* or {@code null} if the lock could not be acquired
* because another program holds an overlapping lock
*
* @throws ClosedChannelException
* If this channel is closed
* @throws OverlappingFileLockException
* If a lock that overlaps the requested region is already held by
* this Java virtual machine, or if another thread is already
* blocked in this method and is attempting to lock an overlapping
* region
* @throws NonWritableChannelException
* If {@code shared} is false but this channel was not opened for writing
*
* @throws IOException
* If some other I/O error occurs
*
* @see #lock(Object,CompletionHandler)
* @see #lock(long,long,boolean,Object,CompletionHandler)
* @see #tryLock(long,long,boolean)
*/
public final FileLock tryLock() throws IOException {
return tryLock(0L, Long.MAX_VALUE, false);
}
/**
* Reads a sequence of bytes from this channel into the given buffer,
* starting at the given file position.
*
* <p> This method initiates the reading of a sequence of bytes from this
* channel into the given buffer, starting at the given file position. The
* result of the read is the number of bytes read or {@code -1} if the given
* position is greater than or equal to the file's size at the time that the
* read is attempted.
*
* <p> This method works in the same manner as the {@link
* AsynchronousByteChannel#read(ByteBuffer,Object,CompletionHandler)}
* method, except that bytes are read starting at the given file position.
* If the given file position is greater than the file's size at the time
* that the read is attempted then no bytes are read.
*
* @param <A>
* The type of the attachment
* @param dst
* The buffer into which bytes are to be transferred
* @param position
* The file position at which the transfer is to begin;
* must be non-negative
* @param attachment
* The object to attach to the I/O operation; can be {@code null}
* @param handler
* The handler for consuming the result
*
* @throws IllegalArgumentException
* If the position is negative or the buffer is read-only
* @throws NonReadableChannelException
* If this channel was not opened for reading
*/
public abstract <A> void read(ByteBuffer dst,
long position,
A attachment,
CompletionHandler<Integer,? super A> handler);
/**
* Reads a sequence of bytes from this channel into the given buffer,
* starting at the given file position.
*
* <p> This method initiates the reading of a sequence of bytes from this
* channel into the given buffer, starting at the given file position. This
* method returns a {@code Future} representing the pending result of the
* operation. The {@code Future}'s {@link Future#get() get} method returns
* the number of bytes read or {@code -1} if the given position is greater
* than or equal to the file's size at the time that the read is attempted.
*
* <p> This method works in the same manner as the {@link
* AsynchronousByteChannel#read(ByteBuffer)} method, except that bytes are
* read starting at the given file position. If the given file position is
/**代码未完, 请加载全部代码(NowJava.com).**/
关注时代Java
关注时代Java