Java读取文件转换成byte[]的小结

1、FileInputStream

	/**
	 * 
	 * 
Title: getContent
  
	 * 
Description:根据文件路径读取文件转出byte[] 
  
	 * @param filePath文件路径
	 * @return 字节数组
	 * @throws IOException
	 */
	public static byte[] getContent(String filePath) throws IOException { 
        File file = new File(filePath);  
        long fileSize = file.length();  
        if (fileSize > Integer.MAX_VALUE) {  
        	logger.info("file too big...");  
            return null;  
        }  
        FileInputStream fi = new FileInputStream(file);  
        byte[] buffer = new byte[(int) fileSize];  
        int offset = 0;  
        int numRead = 0;  
        while (offset < buffer.length  
        && (numRead = fi.read(buffer, offset, buffer.length - offset)) >= 0) {  
            offset += numRead;  
        }  
        // 确保所有数据均被读取  
        if (offset != buffer.length) {  
        	throw new IOException("Could not completely read file "  
                    + file.getName());  
        }  
        fi.close();  
        return buffer;  
    }

2、ByteArrayOutputStream和BufferedInputStream传统的IO

/**
	 * 
	 * 
Title: toByteArray
  
	 * 
Description: 传统的IO流方式
  
	 * @param filename
	 * @return
	 * @throws IOException
	 */
	public static byte[] toByteArray(String filename) throws IOException {
		File file = new File(filename);
		if (!file.exists()) {
			throw new FileNotFoundException(filename);
		}
		ByteArrayOutputStream bos = new ByteArrayOutputStream((int) file.length());
		BufferedInputStream in = null;
		try {
			in = new BufferedInputStream(new FileInputStream(file));
			int buf_size = 1024;
			byte[] buffer = new byte[buf_size];
			int len = 0;
			while (-1 != (len = in.read(buffer, 0, buf_size))) {
				bos.write(buffer, 0, len);
			}
			return bos.toByteArray();
		} catch (IOException e) {
			e.printStackTrace();
			throw e;
		} finally {
			try {
				bos.close();
				in.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
			bos.close();
		}
	}

3、NIO

/**
	 * 
	 * 
Title: toByteArrayNIO
  
	 * 
Description: NIO way
  
	 * @param filename
	 * @return
	 * @throws IOException
	 */
	public static byte[] toByteArrayNIO(String filename) throws IOException {
		File file = new File(filename);
		if (!file.exists()) {
			throw new FileNotFoundException(filename);
		}
		FileChannel channel = null;
		FileInputStream fs = null;
		try {
			fs = new FileInputStream(file);
			channel = fs.getChannel();
			ByteBuffer byteBuffer = ByteBuffer.allocate((int) channel.size());
			while (channel.read(byteBuffer) > 0) {
				// do nothing
				// System.out.println("reading");
			}
			return byteBuffer.array();
		} catch (Exception e) {
			e.printStackTrace();
			throw e;
		} finally {
			try {
				channel.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
			try {
				fs.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
	

4、RandomAccessFile和MappedByteBuffer读取大文件

/**
	 * 
	 * 
Title: toByteArrayMapped
  
	 * 
Description: 读取大文件
  
	 * @param filename
	 * @return
	 * @throws IOException
	 */
	 public static byte[] toByteArrayMapped(String filename) throws IOException {  

		FileChannel fc = null;
		RandomAccessFile rf=new RandomAccessFile(filename, "r");
		try {
//			fc = new RandomAccessFile(filename, "r").getChannel();
			fc = rf.getChannel();
			MappedByteBuffer mappedByteBuffer = fc.map(MapMode.READ_ONLY, 0, fc.size()).load();
			logger.info("{}", mappedByteBuffer.isLoaded());
			byte[] result = new byte[(int) fc.size()];
			if (mappedByteBuffer.remaining() > 0) {  
                // System.out.println("remain");  
				mappedByteBuffer.get(result, 0, mappedByteBuffer.remaining());  
            }
			return result; 
		}  catch (IOException e) {  
            e.printStackTrace();  
            throw e;  
        } finally {  
            try {  
            	rf.close();
                fc.close();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  

	}