Java FileChannel.read方法代码示例

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
public static void main(String[] args) throws IOException {
    RandomAccessFile aFile = new RandomAccessFile("/Users/zhenpeng/aa.txt", "rw");
    FileChannel inChannel = aFile.getChannel();
    ByteBuffer buf = ByteBuffer.allocate(2);
    int bytesRead = inChannel.read(buf);
    while (bytesRead != -1) {
        buf.flip();
        while (buf.hasRemaining()) {
            System.out.print((char) buf.get());
        }
        buf.clear();
        //bytesRead = inChannel.read(buf);
        //buf.putChar('f');
        bytesRead = inChannel.read(buf);
    }
    aFile.close();
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
/**
 * Extracts the raw ID3v2 tag data into a file.
 * <p/>
 * This provides access to the raw data before manipulation, the data is written from the start of the file
 * to the start of the Audio Data. This is primarily useful for manipulating corrupted tags that are not
 * (fully) loaded using the standard methods.
 *
 * @param outputFile to write the data to
 * @return
 * @throws TagNotFoundException
 * @throws IOException
 */
public File extractID3v2TagDataIntoFile(File outputFile) throws TagNotFoundException, IOException {
    int startByte = (int) ((MP3AudioHeader) audioHeader).getMp3StartByte();
    if (startByte >= 0) {

        //Read byte into buffer
        FileInputStream fis = new FileInputStream(file);
        FileChannel fc = fis.getChannel();
        ByteBuffer bb = ByteBuffer.allocate(startByte);
        fc.read(bb);

        //Write bytes to outputFile
        FileOutputStream out = new FileOutputStream(outputFile);
        out.write(bb.array());
        out.close();
        fc.close();
        fis.close();
        return outputFile;
    }
    throw new TagNotFoundException("There is no ID3v2Tag data in this file");
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
/**
 * FileChannel 负责文件的读写
 * @throws IOException
 */
public void fileChannelExa() throws IOException {

    String filePath = BasicChannelExample.class.getClassLoader().getResource("data/nio-data.txt").getFile();
    RandomAccessFile aFile = new RandomAccessFile(filePath , "rw");

    FileChannel inChannel = aFile.getChannel();

    ByteBuffer buf = ByteBuffer.allocate(48);

    int bytesRead = inChannel.read(buf);
    while (bytesRead != -1) {

        System.out.println("Read " + bytesRead);
        buf.flip();

        while(buf.hasRemaining()){
            System.out.print((char) buf.get());
        }

        buf.clear();
        bytesRead = inChannel.read(buf);
    }
    aFile.close();
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
/**
 * 读取文件到字节数组中
 *
 * @param file 文件
 * @return 字符数组
 */
public static byte[] readFile2BytesByChannel(File file) {
    if (!FileUtils.isFileExists(file)) return null;
    FileChannel fc = null;
    try {
        fc = new RandomAccessFile(file, "r").getChannel();
        ByteBuffer byteBuffer = ByteBuffer.allocate((int) fc.size());
        while (true) {
            if (!((fc.read(byteBuffer)) > 0)) break;
        }
        return byteBuffer.array();
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    } finally {
        CloseUtils.closeIO(fc);
    }
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
public static long getNextTokenSize(FileChannel fileChannel, long position, byte[]... btsArr)
    throws IOException {
  long ret = -1;
  ByteBuffer buffer = ByteBuffer.allocateDirect(8192);
  if (position >= 0) {
    fileChannel.position(position);
  }
  long startPosition = fileChannel.position();
  outer:
  while (fileChannel.read(buffer) != -1) {
    buffer.flip();
    int index;
    while ((index = findBytes(buffer, btsArr)) != -1) {
      ret = fileChannel.position() - startPosition - buffer.limit() + index;
      break outer;
    }
    buffer.clear();
  }
  fileChannel.position(startPosition);
  return ret;
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
/**
 * Read the header without changing the position of the FileChannel.
 *
 * @param fc The FileChannel to read.
 * @return the Metadata Header.
 * @throws IOException on error.
 */
public static BlockMetadataHeader preadHeader(FileChannel fc)
    throws IOException {
  final byte arr[] = new byte[getHeaderSize()];
  ByteBuffer buf = ByteBuffer.wrap(arr);

  while (buf.hasRemaining()) {
    if (fc.read(buf, 0) <= 0) {
      throw new EOFException("unexpected EOF while reading " +
          "metadata file header");
    }
  }
  short version = (short)((arr[0] << 8) | (arr[1] & 0xff));
  DataChecksum dataChecksum = DataChecksum.newDataChecksum(arr, 2);
  return new BlockMetadataHeader(version, dataChecksum);
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
public static long findCentralDirStartOffset(final FileChannel fileChannel, final long commentLength) throws IOException {
    // End of central directory record (EOCD)
    // Offset    Bytes     Description[23]
    // 0           4       End of central directory signature = 0x06054b50
    // 4           2       Number of this disk
    // 6           2       Disk where central directory starts
    // 8           2       Number of central directory records on this disk
    // 10          2       Total number of central directory records
    // 12          4       Size of central directory (bytes)
    // 16          4       Offset of start of central directory, relative to start of archive
    // 20          2       Comment length (n)
    // 22          n       Comment
    // For a zip with no archive comment, the
    // end-of-central-directory record will be 22 bytes long, so
    // we expect to find the EOCD marker 22 bytes from the end.

    final ByteBuffer zipCentralDirectoryStart = ByteBuffer.allocate(4);
    zipCentralDirectoryStart.order(ByteOrder.LITTLE_ENDIAN);
    fileChannel.position(fileChannel.size() - commentLength - 6); // 6 = 2 (Comment length) + 4 (Offset of start of central directory, relative to start of archive)
    fileChannel.read(zipCentralDirectoryStart);
    final long centralDirStartOffset = zipCentralDirectoryStart.getInt(0);
    return centralDirStartOffset;
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
/**
 * Use ByteBuffers to copy a 4mb chunk, write the chunk and repeat until the rest of the file after the ID3 tag
 * is rewritten
 *
 * @param existingTag    existing tag
 * @param channel        channel
 * @param newLength      new length
 * @param lengthTagChunk length tag chunk
 * @throws IOException if something goes wrong
 */
// TODO: arguments are not used, position is implicit
private void deleteTagChunkUsingSmallByteBufferSegments(final AiffTag existingTag, final FileChannel channel, final long newLength, final long lengthTagChunk)
        throws IOException {
    final ByteBuffer buffer = ByteBuffer.allocateDirect((int) TagOptionSingleton.getInstance().getWriteChunkSize());
    while (channel.read(buffer) >= 0 || buffer.position() != 0) {
        buffer.flip();
        final long readPosition = channel.position();
        channel.position(readPosition - lengthTagChunk - buffer.limit());
        channel.write(buffer);
        channel.position(readPosition);
        buffer.compact();
    }
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
@Override protected void compute() {
  try( FileInputStream s = new FileInputStream(new File(_path))) {
    FileChannel fc = s.getChannel();
    fc.position(_off);
    fc.read(_bb=ByteBuffer.wrap(_chk));
  } catch( Exception e) {
    System.err.println("chunk: " + _cidx + "; bytesToRead: " + _chkSize +"; offset: " + _off);
    throw new RuntimeException(e);
  }
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
private boolean loadBaseAndCheckByFileChannel(String path) {
    try {
        FileInputStream fis = new FileInputStream(path);
        // 1.从FileInputStream对象获取文件通道FileChannel
        FileChannel channel = fis.getChannel();
        int fileSize = (int) channel.size();

        // 2.从通道读取文件内容
        ByteBuffer byteBuffer = ByteBuffer.allocate(fileSize);

        // channel.read(ByteBuffer) 方法就类似于 inputstream.read(byte)
        // 每次read都将读取 allocate 个字节到ByteBuffer
        channel.read(byteBuffer);
        // 注意先调用flip方法反转Buffer,再从Buffer读取数据
        byteBuffer.flip();
        // 有几种方式可以操作ByteBuffer
        // 可以将当前Buffer包含的字节数组全部读取出来
        byte[] bytes = byteBuffer.array();
        byteBuffer.clear();
        // 关闭通道和文件流
        channel.close();
        fis.close();

        int index = 0;
        size = ByteUtil.bytesHighFirstToInt(bytes, index);
        index += 4;
        base = new int[size + 65535];   // 多留一些，防止越界
        check = new int[size + 65535];
        for (int i = 0; i < size; i++) {
            base[i] = ByteUtil.bytesHighFirstToInt(bytes, index);
            index += 4;
            check[i] = ByteUtil.bytesHighFirstToInt(bytes, index);
            index += 4;
        }
    } catch (Exception e) {
        return false;
    }
    return true;
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
@Test
void testAll() throws Exception {
    initChannel("testAll");

    assertFalse(s3channel.hasDelayedHeader());
    assertEquals(0, s3channel.headerSize());

    final FileChannel fc = FileChannel.open(file.path, StandardOpenOption.READ);
    final ByteBuffer chunk = ByteBuffer.allocate(chunkSize);

    int todo = (int) file.size;
    while (todo >= chunkSize) {
        chunk.rewind();
        fc.read(chunk);
        chunk.rewind();
        assertEquals(chunkSize, s3channel.write(chunk));
        todo -= chunkSize;
    }
    if (todo > 0) {
        chunk.rewind();
        chunk.limit(todo);
        assertEquals(todo, fc.read(chunk));
        assertEquals(fc.position(), fc.size());
        chunk.rewind();
        assertEquals(todo, s3channel.write(new ByteBuffer[] { chunk }));
    }

    // setting lower position does not make any effect
    assertEquals(s3channel.position(s3channel.position() - 100).position(), s3channel.size());

    fc.close();
    s3channel.close();
    assertFalse(s3channel.isOpen());

    verifyFileContentEquality();
    file.close();
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
/**
 *
 * @param fc
 * @param size
 * @return
 * @throws IOException
 */
public static ByteBuffer readFileDataIntoBufferBE(FileChannel fc, final int size) throws IOException
{
    final ByteBuffer tagBuffer = ByteBuffer.allocateDirect(size);
    fc.read(tagBuffer);
    tagBuffer.position(0);
    tagBuffer.order(ByteOrder.BIG_ENDIAN);
    return tagBuffer;
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
/**
 * Reads as much as possible from the channel into the buffer.
 * 
 * @param channel The channel.
 * @param buffer The buffer.
 * @param ptr The initial position in the channel.
 * @throws IOException if an I/O error occurs.
 */
public static void readFully(FileChannel channel, ByteBuffer buffer, long ptr) throws IOException {
	while (buffer.remaining() > 0) {
		long read = channel.read(buffer, ptr);
		if (read < -1) {
			throw new EOFException();
		} else {
			ptr += read;
		}
	}
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
@Override
public ResponseEntity<StreamingResponseBody> readFile(String fileLocation, String imageDir, String id,
		String fileName) {
	StreamingResponseBody streamingResponseBody = new StreamingResponseBody() {

		@Override
		public void writeTo(OutputStream outputStream) {
			try {

				String fileStr = fileLocation + File.separator + imageDir + File.separator + id + File.separator
						+ fileName;

				RandomAccessFile file = new RandomAccessFile(fileStr, "r");
				FileChannel inChannel = file.getChannel();
				ByteBuffer buffer = ByteBuffer.allocate(1024);
				while (inChannel.read(buffer) > 0) {
					buffer.flip();
					for (int i = 0; i < buffer.limit(); i++) {
						outputStream.write(buffer.get());
					}
					buffer.clear();
					outputStream.flush();
				}
				inChannel.close();
				file.close();

			} catch (IOException e) {
				logger.error("Image Not Found : error " + e.getMessage());
				throw new ResourceNotFoundException("Image Not Found : " + id + "/" + fileName);
			}
		}
	};

	HttpHeaders headers = new HttpHeaders();
	headers.add(HttpHeaders.CONTENT_TYPE, "image/*");
	return new ResponseEntity<StreamingResponseBody>(streamingResponseBody, headers, HttpStatus.OK);
}
 

import java.nio.channels.FileChannel; //导入方法依赖的package包/类
public String telnet(Channel channel, String message) {
    long size = 0 ;
    File file = LoggerFactory.getFile();
    StringBuffer buf = new StringBuffer();
    if (message == null || message.trim().length() == 0) {
        buf.append("EXAMPLE: log error / log 100");
    }else {
        String str[] = message.split(" ");
        if (! StringUtils.isInteger(str[0])){
            LoggerFactory.setLevel(Level.valueOf(message.toUpperCase()));
        } else {
            int SHOW_LOG_LENGTH = Integer.parseInt(str[0]);
            
            if (file != null && file.exists()) {
                try{
                    FileInputStream fis = new FileInputStream(file);
                    try {
                     FileChannel filechannel = fis.getChannel();
                     try {
                      size = filechannel.size();
                      ByteBuffer bb;
                      if (size <= SHOW_LOG_LENGTH) {
                          bb = ByteBuffer.allocate((int) size);
                          filechannel.read(bb, 0);
                      } else {
                          int pos = (int) (size - SHOW_LOG_LENGTH);
                          bb = ByteBuffer.allocate(SHOW_LOG_LENGTH);
                          filechannel.read(bb, pos);
                      }
                      bb.flip();
                      String content = new String(bb.array()).replace("<", "&lt;")
                      .replace(">", "&gt;").replace("\n", "<br/><br/>");
                      buf.append("\r\ncontent:"+content);
                      
                      buf.append("\r\nmodified:"+(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss")
                      .format(new Date(file.lastModified()))));
                      buf.append("\r\nsize:"+size +"\r\n");
                     } finally {
                     	filechannel.close();
                     }
                    } finally {
                    	fis.close();
                    }
                }catch (Exception e) {
                    buf.append(e.getMessage());
                }
            }else {
                size = 0;
                buf.append("\r\nMESSAGE: log file not exists or log appender is console .");
            }
        }
    }
    buf.append("\r\nCURRENT LOG LEVEL:"+ LoggerFactory.getLevel())
    .append("\r\nCURRENT LOG APPENDER:"+ (file == null ? "console" : file.getAbsolutePath()));
    return buf.toString();
}