java中MultipartFile和File最简单的互相转换示例

public File multipartFile2File (MultipartFile multipartFile) {
    // 创建临时文件
    String path = "export/demo.xlsx";
    File file = new File(path);
    InputStream inputStream = null;
    FileOutputStream outputStream = null;
    try {
        // 获取文件输入流
        inputStream = multipartFile.getInputStream();
        if (!file.exists()) {
            file.createNewFile();
        }
        // 创建输出流
        outputStream = new FileOutputStream(file);
        byte[] bytes = new byte[1024];
        int len;
        // 写入到创建的临时文件
        while ((len = inputStream.read(bytes)) > 0) {
            outputStream.write(bytes, 0, len);
        }
    } catch (Exception e) {
        throw new RuntimeException(e);
    } finally {
        // 关流
        try {
            if (outputStream != null) {
                outputStream.close();
            }
            if (outputStream != null) {
                inputStream.close();
            }
            outputStream.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
    return file;
}

public File multipartFile2File (MultipartFile multipartFile) {
    String path = "export/demo.xlsx";
    File file = new File(path);
    try {
        if (!file.exists()) {
            file.createNewFile();
        }
        // 底层也是通过io流写入文件file
        FileCopyUtils.copy(multipartFile.getBytes(), file);
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
    return file;
}

public MultipartFile file2MultipartFile () {
    String path = "export/demo.xlsx";
    File file = new File(path);
    MultipartFile multipartFile;
    try {
        FileInputStream fileInputStream = new FileInputStream(file);
        multipartFile = new MockMultipartFile("copy"+file.getName(),file.getName(), ContentType.APPLICATION_OCTET_STREAM.toString(),fileInputStream);
        System.out.println(multipartFile.getName()); // 输出demo.xlsx
        fileInputStream.close();
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
    return multipartFile;
}

public MultipartFile file2MultipartFile () {
    String path = "export/demo.xlsx";
    File file = new File(path);
    MultipartFile multipartFile;
    try {
        DiskFileItem fileItem2 = (DiskFileItem) new DiskFileItemFactory().createItem("file", ContentType.MULTIPART.getValue(), true, file.getName());
        //也可以用IOUtils.copy(inputStream,os);
        Files.copy(Paths.get(file.getAbsolutePath()), fileItem2.getOutputStream());
        multipartFile = new CommonsMultipartFile(fileItem2);
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
    return multipartFile;
}