code: public byte[] readBoundary() throws IOException {
  		ByteArrayOutputStream boundaryOutput = new ByteArrayOutputStream(1024);
  		byte b;
  		// skip optional whitespaces
  		while ((b = readByte()) <= ' ') {
  		}
  		boundaryOutput.write(b);
  
  		// now read boundary chars
  		while ((b = readByte()) != '\r') {
  			boundaryOutput.write(b);
  		}
  		if (boundaryOutput.size() == 0) {
  			throw new IOException("Problems with parsing request: invalid boundary");
  		}
  		skipBytes(1);
  		boundary = new byte[boundaryOutput.size() + 2];
  		System.arraycopy(boundaryOutput.toByteArray(), 0, boundary, 2, boundary.length - 2);
  		boundary[0] = '\r';
  		boundary[1] = '\n';
  		return boundary;
  	}
docs: 输入流中读取边界
  
  @return 边界
  @throws IOException