从文件得到ByteArrayOutputStream

public static ByteArrayOutputStream getOutputStream(String filePath){

    File file = new File(filePath);
    FileInputStream in = null;
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    try {
      in = new FileInputStream(file);
      byte[] buffer = new byte[in.available()];
      in.read(buffer);
      out.write(buffer);

    } catch (Exception e) {
      e.printStackTrace();
    }finally{
      try {
        if(in!=null) in.close();
      } catch (Exception e2) {
      }

    }
    return out;
  }