/**
   * Creates and initializes an SPV block store. Will create the given file if it's missing. This
   * operation will block on disk.
   */
  public SPVBlockStore(NetworkParameters params, File file) throws BlockStoreException {
    checkNotNull(file);
    this.params = checkNotNull(params);
    try {
      this.numHeaders = DEFAULT_NUM_HEADERS;
      boolean exists = file.exists();
      // Set up the backing file.
      randomAccessFile = new RandomAccessFile(file, "rw");
      long fileSize = getFileSize();
      if (!exists) {
        log.info("Creating new SPV block chain file " + file);
        randomAccessFile.setLength(fileSize);
      } else if (randomAccessFile.length() != fileSize) {
        throw new BlockStoreException(
            "File size on disk does not match expected size: "
                + randomAccessFile.length()
                + " vs "
                + fileSize);
      }

      FileChannel channel = randomAccessFile.getChannel();
      fileLock = channel.tryLock();
      if (fileLock == null)
        throw new BlockStoreException("Store file is already locked by another process");

      // Map it into memory read/write. The kernel will take care of flushing writes to disk at the
      // most
      // efficient times, which may mean that until the map is deallocated the data on disk is
      // randomly
      // inconsistent. However the only process accessing it is us, via this mapping, so our own
      // view will
      // always be correct. Once we establish the mmap the underlying file and channel can go away.
      // Note that
      // the details of mmapping vary between platforms.
      buffer = channel.map(FileChannel.MapMode.READ_WRITE, 0, fileSize);

      // Check or initialize the header bytes to ensure we don't try to open some random file.
      byte[] header;
      if (exists) {
        header = new byte[4];
        buffer.get(header);
        if (!new String(header, "US-ASCII").equals(HEADER_MAGIC))
          throw new BlockStoreException("Header bytes do not equal " + HEADER_MAGIC);
      } else {
        initNewStore(params);
      }
    } catch (Exception e) {
      try {
        if (randomAccessFile != null) randomAccessFile.close();
      } catch (IOException e2) {
        throw new BlockStoreException(e2);
      }
      throw new BlockStoreException(e);
    }
  }
  /*
   * TODO: Finish method.
   */
  public static String readBytesFromFile(File filename)
      throws IOException, OverlappingFileLockException {
    if (!filename.exists()) {
      return null;
    }

    try {
      ByteBuffer buffer = ByteBuffer.allocate(((int) filename.getTotalSpace() * 4));
      fileReader = new FileInputStream(filename).getChannel();
      FileLock lock = fileReader.tryLock();

      if (lock != null) {
        fileReader.read(buffer);
      } else {
        throw new OverlappingFileLockException();
      }
    } finally {
      fileWriter.close();
    }

    return "";
  }
Exemple #3
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 public static FileLock lock_file(String path) throws IOException, FileNotFoundException {
   RandomAccessFile file = new RandomAccessFile(path, "rw");
   FileChannel fileChannel = file.getChannel();
   return fileChannel.tryLock();
 }