文件处理中 各种常见数据类型转换 相当于各种轮子的汇总 inputstream；base64；byte[],blob；图片；pdf；word等。。。

word转pdf:基于spire free免费版 可以进行word转pdf word转图片  免费版仅限于三页  商业还是老老实实买jar包，不商用可搜索aspose spire.doc等jar包进行学习。

public String wordToPdf(String path) throws IOException {
        // 加载word示例文档
        Document document = new Document();
        document.loadFromFile(path);
        // 保存结果文件
        document.saveToFile("D:\\test3.pdf");
        return "转换成功";

    }

 PDF转图片：

public  void pdfFileToImages(String filePath, String cachePath) {
        try {
            PDDocument pd = PDDocument.load(new File(filePath));
            PDFRenderer pdfRenderer = new PDFRenderer(pd);
            for (int page = 0; page < pd.getNumberOfPages(); ++page) {
                BufferedImage image = pdfRenderer.renderImageWithDPI(page, 96, ImageType.RGB);
                //将图片数据保存为PNG格式文档
                File file= new File(cachePath + File.separator + page + ".png");
                ImageIO.write(image, "png", file);
                System.out.println(file.getAbsolutePath());
            }
        }  catch (Exception e) {
            e.printStackTrace();
        }
    }

bufferedImage转MultipartFile word和pdf转图片经常需要：

public  MultipartFile bufferedImageToMultipartFile(BufferedImage bufferedImage, String fileName) throws IOException {
            //创建一个ByteArrayOutputStream
            ByteArrayOutputStream os = new ByteArrayOutputStream();
            //把BufferedImage写入ByteArrayOutputStream
            ImageIO.write(bufferedImage, "png", os);
            //ByteArrayOutputStream转成InputStream
            InputStream input = new ByteArrayInputStream(os.toByteArray());
            //InputStream转成MultipartFile
            MultipartFile multipartFile = new MockMultipartFile(fileName, fileName + ".png", "text/plain", input);
            return multipartFile;
        }

outputStream转inputStream

public  ByteArrayInputStream parse(OutputStream out) throws Exception {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            baos = (ByteArrayOutputStream) out;
            ByteArrayInputStream swapStream = new ByteArrayInputStream(baos.toByteArray());
            return swapStream;
        }

file转byte[]:

public static byte[] filetobyte(File file) {
        byte[] fileBytes = new byte[0];
        try {
            FileInputStream fis = new FileInputStream(file);
            // 强转成int类型大小的数组
            fileBytes = new byte[(int) file.length()];
            // 将pdf内容放到数组当中
            fis.read(fileBytes);
            // 关闭文件流
            fis.close();
            // System.out.println(Arrays.toString(fileBytes));
        } catch (
                IOException e) {
            e.printStackTrace();
        }
        return fileBytes;
    }

MultipartFile转file

 public static File MultipartFileToFile(MultipartFile mFile) throws IOException {
        File file = new File(mFile.getOriginalFilename());
        FileUtils.copyInputStreamToFile(mFile.getInputStream(), file);
        //这种方法会在本地产生临时文件，用完后需要删除
        //if (file.exists()) {
        //    file.delete();
        //}
        return file;
    }

MultipartFilez转base64

public static String MultipartFileToBase64(MultipartFile file) throws Exception {
        BASE64Encoder base64Encoder = new BASE64Encoder();
        String base64EncoderImg = file.getOriginalFilename() + "," + base64Encoder.encode(file.getBytes());
        return base64EncoderImg;
    }

String转base64

public static String StringToBase64(String token) {
        byte[] bytes = token.getBytes();
        Base64.Encoder encoder = Base64.getEncoder();
        String encodeToken = encoder.encodeToString(bytes);
        return encodeToken;
    }

file转base64

public static String fileToBase64(File file) {
        String base64 = null;
        InputStream in = null;
        try {
            in = new FileInputStream(file);
            byte[] bytes = new byte[(int) file.length()];
            in.read(bytes);
            base64 = Base64.getEncoder().encodeToString(bytes);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        System.out.println(base64);
        return base64;
    }

 inputstream转multipartFile

MultipartFile multipartFile = new MockMultipartFile(fileName, fileName + ".docx", "text/plain", inputStream);

base64转inputstream

String base64FileData = "";
BASE64Decoder decoder = new BASE64Decoder();
// Base64解码
byte[] byteArr = decoder.decodeBuffer(base64FileData);
InputStream inputStream = new ByteArrayInputStream(byteArr);