讀取文件位並保存它們

Question

我有讀取整個文件並將其寫入的文件讀取器。 我有這節課，可以幫助閱讀：

import java.io.*;

public class FileReader extends ByteArrayInputStream{

  private int bitsRead;
  private int bitPosition;
  private int currentByte;
  private int myMark;
  private final static int NUM_BITS_IN_BYTE = 8;
  private final static int END_POSITION = -1;
  private boolean readingStarted;
  /**
   * Create a BitInputStream for a File on disk.
   */
  public FileReader( byte[] buf ) throws IOException {
    super( buf );

    myMark         = 0;
    bitsRead       = 0;
    bitPosition    = NUM_BITS_IN_BYTE-1;
    currentByte    = 0;
    readingStarted = false;
  }


  /**
   * Read a binary "1" or "0" from the File.
   */
  public int readBit() throws IOException {
    int theBit = -1;

    if( bitPosition == END_POSITION || !readingStarted ) {
      currentByte    = super.read();
      bitPosition    = NUM_BITS_IN_BYTE-1;
      readingStarted = true;
    }

    theBit = (0x01 << bitPosition) & currentByte;
    bitPosition--;

    if( theBit > 0 ) {
      theBit = 1;
    }

    return( theBit );
  }


  /**
   * Return the next byte in the File as lowest 8 bits of int.
   */
  public int read() {
    currentByte    = super.read();
    bitPosition    = END_POSITION;
    readingStarted = true;

    return( currentByte );
  }


  /**
   *
   */
  public void mark( int readAheadLimit ) {
    super.mark(readAheadLimit);
    myMark = bitPosition;
  }


  /**
   * Add needed functionality to super's reset() method. Reset to
   * the last valid position marked in the input stream.
   */
  public void reset() {
    super.pos   = super.mark-1;
    currentByte = super.read();
    bitPosition = myMark;
  }


  /**
   * Returns the number of bits still available to be read.
   */
  public int availableBits() throws IOException {
    return(  ((super.available() * 8) + (bitPosition + 1))  );
  }

}

在我稱之為的課堂上，我這樣做：

FileInputStream inputStream = new FileInputStream(file);

        byte[] fileBits = new byte[inputStream.available()];

        inputStream.read(fileBits, 0, inputStream.available());
        inputStream.close();

        FileReader bitIn = new FileReader(fileBits);      

並且可以正常工作。 但是我對100 mb以上的大文件有問題，因為byte []結尾。

所以我想閱讀更大的文件。 也許有人可以建議我如何改進此代碼？

謝謝。

Answer 1

org.apache.commons.io.IOUtils.copy(InputStream in, OutputStream out)

Answer 2

如果縮放到大文件很重要，最好不要將整個文件讀到內存中。 缺點是在更多位置處理IOException可能會有些混亂。 另外，看起來您的應用程序不需要實現InputStream API的東西，而只需要readBit()方法。 因此，您可以安全地封裝而不是擴展InputStream 。

class FileReader {

  private final InputStream src;

  private final byte[] bits = new byte[8192];

  private int len;

  private int pos;

  FileReader(InputStream src) { 
    this.src = src; 
  }

  int readBit() throws IOException {
    int idx = pos / 8;
    if (idx >= len) {
      int n = src.read(bits);
      if (n < 0)
        return -1;
      len = n;
      pos = 0;
      idx = 0;
    }
    return ((bits[idx] & (1 << (pos++ % 8))) == 0) ? 0 : 1;
  }

}

用法看起來類似。

FileInputStream src = new FileInputStream(file);
try {
  FileReader bitIn = new FileReader(src);
  ...
} finally {
  src.close();
}

如果您確實確實想讀取整個文件，並且正在使用實際文件，則可以先查詢文件的長度。

File file = new File(path);
if (file.length() > Integer.MAX_VALUE)
  throw new IllegalArgumentException("File is too large: " + file.length());
int len = (int) file.length();
FileInputStream inputStream = new FileInputStream(file);
try { 
  byte[] fileBits = new byte[len];
  for (int pos = 0; pos < len; ) {
    int n = inputStream.read(fileBits, pos, len - pos);
    if (n < 0)
      throw new EOFException();
    pos += n;
  }
  /* Use bits. */
  ...
} finally {
  inputStream.close();
}