Java io流文件读取和写入

 /**
     *@author lxw
     *@date 2020/6/24
     *@desc 获取文件输入流，这里读入内存中
     *@param [fileName]
     *@return byte[]
    **/
    public byte[] readPdfFile(String fileName) throws Exception{
        InputStream in = null;
        byte[] bytesRel;
        try {
            //读取Constants.PDF_CREATE_AND_SIGN.PDF_FILE_PATH路径下文件名位fileName的文件
            File f = new File(Constants.PDF_CREATE_AND_SIGN.PDF_FILE_PATH+fileName);
            in = new FileInputStream(f);
            //in.available 只适合于读取本地文件时判断流中字节数，不适合网络中的流数据大小判定
            bytesRel = new byte[ in.available()];
            in.read(bytesRel);
        } catch (IOException e) {
          log.error("读取文件{}失败！"+Constants.PDF_CREATE_AND_SIGN.PDF_FILE_PATH+fileName);
          throw new BizException(IfspRespCode.RESP_ERROR,"读取pdf文件失败！");
        }finally {
            if (in != null){
                try {
                    in.close();
                } catch (IOException e) {
                    log.error("输入流关闭失败！原因：{}",e.getMessage());
                }
            }
        }
        return  bytesRel;
    }

 /**
     *@author lxw
     *@date 2020/6/24
     *@desc 写文件 如果想提高效率，可以使用缓冲流
     *@param [pdfByte, fileName]
     *@return void
    **/
    public void writePdfFile(byte[] pdfByte,String fileName) throws Exception{
        //检查文件是否已经存在，存在删除
        checkFIleExit(fileName,Constants.PDF_CREATE_AND_SIGN.PDF_FILE_PATH);
        OutputStream os = null;
        try {
            os = new FileOutputStream(Constants.PDF_CREATE_AND_SIGN.PDF_FILE_PATH+fileName);
            os.write( pdfByte ) ;
            os.flush() ;
        } catch (IOException e) {
            log.error("写入文件{}失败！"+Constants.PDF_CREATE_AND_SIGN.PDF_FILE_PATH+fileName);
        }finally {
            try {
                if (os!=null)  os.close();
            } catch (IOException e) {
                log.error("输入流关闭失败！原因：{}",e.getMessage());
            }
        }
    }


 /**
     *@author lxw
     *@date 2020/6/23
     *@desc 检查文件是否存在，存在就删除掉
     *@param [fileName, path]
     *@return void
    **/
    public void checkFIleExit(String fileName,String path){
        log.info("checkFIleExit方法入参：fileName:{},path:{}",fileName,path);
        File file = new File(path+fileName);
        if (file.exists()){
            file.delete();
        }
    }