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1.MultipartFile文件转File

    public File transferToFile(MultipartFile multipartFile) {
//       选择用缓冲区来实现这个转换即使用java 创建的临时文件 使用 MultipartFile.transferto()方法 。File file = null;try {String originalFilename = multipartFile.getOriginalFilename();String[] filename = originalFilename.split("\\.");file=File.createTempFile(filename[0], filename[1]);multipartFile.transferTo(file);file.deleteOnExit();} catch (IOException e) {e.printStackTrace();}return file;}

2.读取文件(txt、json)

 public String readerMethod(File file) throws IOException {FileReader fileReader = new FileReader(file);Reader reader = new InputStreamReader(new FileInputStream(file), "Utf-8");int ch = 0;StringBuffer sb = new StringBuffer();while ((ch = reader.read()) != -1) {sb.append((char) ch);}fileReader.close();reader.close();String jsonStr = sb.toString();return jsonStr;}

3.下载网络文件

   /*** 从网络Url中下载文件-兼容linux** @param urlStr 网络文件地址* @param fileName 要保存的文件名* @param savePath  要保存的文件路径* @throws IOException*/public static void downLoadFromUrl(String urlStr, String fileName, String savePath) throws IOException {URL url = new URL(urlStr);HttpURLConnection conn = (HttpURLConnection) url.openConnection();//设置超时间为3秒conn.setConnectTimeout(2 * 1000);//防止屏蔽程序抓取而返回403错误conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)");//得到输入流InputStream inputStream = conn.getInputStream();//获取自己数组byte[] getData = readInputStream(inputStream);//文件保存位置File saveDir = new File(savePath);if (!saveDir.exists()) {saveDir.mkdir();}File file = new File(saveDir + File.separator + fileName);FileOutputStream fos = new FileOutputStream(file);fos.write(getData);if (fos != null) {fos.close();}if (inputStream != null) {inputStream.close();}}

4.压缩文件

        <!--文件压缩--><dependency><groupId>net.coobird</groupId><artifactId>thumbnailator</artifactId><version>0.4.8</version></dependency>

  //压缩文件Thumbnails.of("完整本地文件地址").scale(1f)//缩放比例.outputQuality(0.5f)//图片质量,在0到1，越接近于1质量越好，越接近于0质量越差。.toFile("压缩完成存放的文件地址");