springboot环境下将File转换成MultipartFile_springboot file转multipartfile

1. 根据File文件对象信息创建DiskFileItem对象。
2. 将File文件内容写入到DiskFileItem对象。
3. 将DiskFileItem对象作为参数放入CommonsMultipartFile构造函数中来创建MultipartFile实例类对象。

代码示例如下：

public static MultipartFile convert(File file) throws IOException {
    DiskFileItem fileItem = new DiskFileItem("file",
            Files.probeContentType(file.toPath()), false,
            file.getName(), (int) file.length(), file.getParentFile());
    IoUtil.copy(Files.newInputStream(file.toPath()), fileItem.getOutputStream());
    return new CommonsMultipartFile(fileItem);
}
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实现输入流和文件名称转换成MultipartFile，代码示例如下：

public static MultipartFile covertMultipartFile(InputStream inputStream, String fileName) throws IOException {
        Assert.notNull(inputStream, "InputStream must not be null");
        Assert.notBlank(fileName, "fileName must not be null");
        DiskFileItemFactory fileItemFactory = new DiskFileItemFactory();
        DiskFileItem fileItem = (DiskFileItem) fileItemFactory.createItem("file",
                MediaType.ALL_VALUE, true, fileName);
        try (OutputStream outputStream = fileItem.getOutputStream()) {
            IOUtils.copy(inputStream, outputStream);
            fileItem.getOutputStream().flush();
            IOUtils.closeQuietly(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        if (fileItem.getSize() == 0) {
            throw new IOException("文件读取失败");
        }
        return new CommonsMultipartFile(fileItem);
    }
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