是否有Java方法为应用程序中的独占使用预先分配驱动器空间?
不要求此空间是单独的文件系统或现有文件系统的一部分(因此很容易成为数据库),但它应该允许保留指定的空间量并允许随机读取/写入具有足够高的吞吐量.
这是我基于JNA的fallocate
解决方案的精简版.主要技巧是获取本机文件描述符.到目前为止,我只在Linux上进行了测试,但它应该适用于所有现代POSIX /非Windows系统.在Windows上没有必要,因为Windows默认情况下不会创建稀疏文件(仅限于StandardOpenOption.SPARSE
),因此RandomAccessFile.setLength(size)
或者FileChannel.write(ByteBuffer.allocate(1), size - 1)
足够.
/** * Provides access to operating system-specific {@code fallocate} and * {@code posix_fallocate} functions. */ public final class Fallocate { private static final boolean IS_LINUX = Platform.isLinux(); private static final boolean IS_POSIX = !Platform.isWindows(); private static final int FALLOC_FL_KEEP_SIZE = 0x01; private final int fd; private int mode; private long offset; private final long length; private Fallocate(int fd, long length) { if (!isSupported()) { throwUnsupported("fallocate"); } this.fd = fd; this.length = length; } public static boolean isSupported() { return IS_POSIX; } public static Fallocate forChannel(FileChannel channel, long length) { return new Fallocate(getDescriptor(channel), length); } public static Fallocate forDescriptor(FileDescriptor descriptor, long length) { return new Fallocate(getDescriptor(descriptor), length); } public Fallocate fromOffset(long offset) { this.offset = offset; return this; } public Fallocate keepSize() { requireLinux("fallocate keep size"); mode |= FALLOC_FL_KEEP_SIZE; return this; } private void requireLinux(String feature) { if (!IS_LINUX) { throwUnsupported(feature); } } private void throwUnsupported(String feature) { throw new UnsupportedOperationException(feature + " is not supported on this operating system"); } public void execute() throws IOException { final int errno; if (IS_LINUX) { final int result = FallocateHolder.fallocate(fd, mode, offset, length); errno = result == 0 ? 0 : Native.getLastError(); } else { errno = PosixFallocateHolder.posix_fallocate(fd, offset, length); } if (errno != 0) { throw new IOException("fallocate returned " + errno); } } private static class FallocateHolder { static { Native.register(Platform.C_LIBRARY_NAME); } private static native int fallocate(int fd, int mode, long offset, long length); } private static class PosixFallocateHolder { static { Native.register(Platform.C_LIBRARY_NAME); } private static native int posix_fallocate(int fd, long offset, long length); } private static int getDescriptor(FileChannel channel) { try { // sun.nio.ch.FileChannelImpl declares private final java.io.FileDescriptor fd final Field field = channel.getClass().getDeclaredField("fd"); field.setAccessible(true); return getDescriptor((FileDescriptor) field.get(channel)); } catch (final Exception e) { throw new UnsupportedOperationException("unsupported FileChannel implementation", e); } } private static int getDescriptor(FileDescriptor descriptor) { try { // Oracle java.io.FileDescriptor declares private int fd final Field field = descriptor.getClass().getDeclaredField("fd"); field.setAccessible(true); return (int) field.get(descriptor); } catch (final Exception e) { throw new UnsupportedOperationException("unsupported FileDescriptor implementation", e); } } }
您可以尝试使用RandomAccessFile对象并使用setLength()方法.
例:
File file = ... //Create a temporary file on the filesystem your trying to reserve. long bytes = ... //number of bytes you want to reserve. RandomAccessFile rf = null; try{ rf = new RandomAccessFile(file, "rw"); //rw stands for open in read/write mode. rf.setLength(bytes); //This will cause java to "reserve" memory for your application by inflating/truncating the file to the specific size. //Do whatever you want with the space here... }catch(IOException ex){ //Handle this... }finally{ if(rf != null){ try{ rf.close(); //Lets be nice and tidy here. }catch(IOException ioex){ //Handle this if you want... } } }
注意:在创建RandomAccessFile对象之前,该文件必须存在.
然后可以使用RandomAccessFile对象读取/写入文件.确保目标文件系统有足够的可用空间.空间可能不是"独占",但您可以随时使用文件锁来执行此操作.
PS:如果您最终意识到硬盘驱动器速度慢且无用(或者从一开始就意味着使用RAM),您可以使用java.nio中的ByteBuffer对象.allocate()和allocateDirect()方法应该足够了.字节缓冲区将被分配到RAM(和可能的SwapFile)中,并且将独占于此java程序.可以通过改变缓冲区的位置来进行随机访问.由于这些缓冲区使用有符号整数来引用位置,因此最大大小限制为2 ^ 31 - 1.
在此处阅读有关RandomAccessFile的更多信息.
在这里阅读有关FileLock(java对象)的更多信息.
在这里阅读更多关于ByteBuffer的信息.