Spring中如何实现MultipartFile和File之间互相转换呢?

File转MultipartFile

方式1:
   使用org.springframework.mock.web.MockMultipartFile进行转换
     这种方式需导入spring-test.jar

方式2:
   借助CommonsMultipartFile对象进行转换

使用org.springframework.mock.web.MockMultipartFile

public static void main(String[] args) throws Exception {
        String filePath = "D:\\test.txt";
        File file = new File(filePath);
        FileInputStream fileInputStream = new FileInputStream(file);
        // MockMultipartFile(String name, @Nullable String originalFilename, 
		//   @Nullable String contentType, InputStream contentStream)
        // 其中originalFilename,String contentType 旧名字，类型  可为空
        // ContentType.APPLICATION_OCTET_STREAM.toString() 需要使用HttpClient的包
        MultipartFile multipartFile = new MockMultipartFile("copy"+file.getName(),
		    file.getName(),ContentType.APPLICATION_OCTET_STREAM.toString(),fileInputStream);
        System.out.println(multipartFile.getName()); // 输出copytest.txt
    }

使用CommonsMultipartFile

public static void main(String[] args) throws Exception {
        String filePath = "D:\\test.txt";
        File file = new File(filePath);
        // 需要导入commons-fileupload的包
        FileItem fileItem = new DiskFileItem("copyfile.txt", 
		   Files.probeContentType(file.toPath()),false,file.getName(),(int)file.length(),file.getParentFile());
        byte[] buffer = new byte[4096];
        int n;
        try (InputStream inputStream = new FileInputStream(file); OutputStream os = fileItem.getOutputStream()){
           while ( (n = inputStream.read(buffer,0,4096)) != -1){
               os.write(buffer,0,n);
           }
            //也可以用IOUtils.copy(inputStream,os);
            MultipartFile multipartFile = new CommonsMultipartFile(fileItem);
            System.out.println(multipartFile.getName());
        }catch (IOException e){
            e.printStackTrace();
        }

    }

MultipartFile转File

实现思路:
    方式1：
	  File转MultipartFile的逆过程
    
	方式2:
	  使用transferTo进行转换

 public static void main(String[] args) throws Exception {
        int n;
        // 得到MultipartFile文件
        MultipartFile multipartFile = getFile();
        File f = null;
        // 输出文件的新name 就是指上传后的文件名称
        System.out.println("getName:"+multipartFile.getName());
        // 输出源文件名称 就是指上传前的文件名称
        System.out.println("Oriname:"+multipartFile.getOriginalFilename());
        // 创建文件
        f = new File(multipartFile.getOriginalFilename());
        try ( InputStream in  = multipartFile.getInputStream(); OutputStream os = new FileOutputStream(f)){
            // 得到文件流。以文件流的方式输出到新文件
            // 可以使用byte[] ss = multipartFile.getBytes();代替while
            byte[] buffer = new byte[4096];
            while ((n = in.read(buffer,0,4096)) != -1){
                os.write(buffer,0,n);
            }
            // 读取文件第一行
            BufferedReader bufferedReader = new BufferedReader(new FileReader(f));
            System.out.println(bufferedReader.readLine());
            // 输出路径
            bufferedReader.close();
        }catch (IOException e){
            e.printStackTrace();
        }
        // 输出file的URL
        System.out.println(f.toURI().toURL().toString());
        // 输出文件的绝对路径
        System.out.println(f.getAbsolutePath());
        // 操作完上的文件 需要删除在根目录下生成的文件
        File file = new File(f.toURI());
        if (file.delete()){
            System.out.println("删除成功");
        }else {
            System.out.println("删除失败");

        }

    }
    /**
     *
     * @Description 返回MultipartFile文件
     * @return org.springframework.web.multipart.MultipartFile
     */
    public static MultipartFile getFile() throws IOException {
        String filePath = "D:\\test.txt";
        File file = new File(filePath);
        FileItem fileItem = new DiskFileItem("copyfile.txt", Files.probeContentType(file.toPath()),false,file.getName(),(int)file.length(),file.getParentFile());
        byte[] buffer = new byte[4096];
        int n;
        try (InputStream inputStream = new FileInputStream(file); OutputStream os = fileItem.getOutputStream()){
            while ( (n = inputStream.read(buffer,0,4096)) != -1){
                os.write(buffer,0,n);
            }
            //也可以用IOUtils.copy(inputStream,os);
            MultipartFile multipartFile = new CommonsMultipartFile(fileItem);
            System.out.println(multipartFile.getName());
            return multipartFile;
        }catch (IOException e){
            e.printStackTrace();
        }
        return null;
    }

使用transferTo

 
public static void main(String[] args) throws Exception {
        String path = "D:\\test\\";
        File file = new File(path,"demo.txt");
        // 得到MultipartFile文件
        MultipartFile multipartFile = getFile();
        /*byte[] ss = multipartFile.getBytes();
        OutputStream os = new FileOutputStream(file);
        os.write(ss);
        os.close();*/
        multipartFile.transferTo(file);
        // 读取文件第一行
        BufferedReader bufferedReader = new BufferedReader(new FileReader(file));
        System.out.println(bufferedReader.readLine());
        // 输出绝对路径
        System.out.println(file.getAbsolutePath());
        bufferedReader.close();
        // 操作完上的文件 需要删除在根目录下生成的文件
        if (file.delete()){
            System.out.println("删除成功");
        }else {
            System.out.println("删除失败");

        }
    }

    /**
     *
     * @Description 返回MultipartFile文件
     * @return org.springframework.web.multipart.MultipartFile
     */
    public static MultipartFile getFile() throws IOException {
        String filePath = "D:\\test.txt";
        File file = new File(filePath);
        FileItem fileItem = new DiskFileItem("copyfile.txt", Files.probeContentType(file.toPath()),false,file.getName(),(int)file.length(),file.getParentFile());
        byte[] buffer = new byte[4096];
        int n;
        try (InputStream inputStream = new FileInputStream(file); OutputStream os = fileItem.getOutputStream()){
            while ( (n = inputStream.read(buffer,0,4096)) != -1){
                os.write(buffer,0,n);
            }
            //也可以用IOUtils.copy(inputStream,os);
            MultipartFile multipartFile = new CommonsMultipartFile(fileItem);
            System.out.println(multipartFile.getName());
            return multipartFile;
        }catch (IOException e){
            e.printStackTrace();
        }
        return null;
    }
(3)：使用FileUtils.copyInputStreamToFile()

也是会生成文件，到最后也是要删除文件

public static void main(String[] args) throws Exception {
        String path = "D:\\demo\\";
        File file = new File(path,"demo.txt");
        // 得到MultipartFile文件
        MultipartFile multipartFile = getFile();
        // 把流输出到文件
        FileUtils.copyInputStreamToFile(multipartFile.getInputStream(),file);
        // 读取文件第一行
        BufferedReader bufferedReader = new BufferedReader(new FileReader(file));
        System.out.println(bufferedReader.readLine());
        // 输出绝对路径
        System.out.println(file.getAbsolutePath());
        bufferedReader.close();
        // 操作完上的文件 需要删除在根目录下生成的文件
        if (file.delete()){
            System.out.println("删除成功");
        }else {
            System.out.println("删除失败");

        }
    }
    /**
     *
     * @Description 返回MultipartFile文件
     * @return org.springframework.web.multipart.MultipartFile
     */
    public static MultipartFile getFile() throws IOException {
        String filePath = "D:\\test.txt";
        File file = new File(filePath);
        FileItem fileItem = new DiskFileItem("copyfile.txt", Files.probeContentType(file.toPath()),false,file.getName(),(int)file.length(),file.getParentFile());
        byte[] buffer = new byte[4096];
        int n;
        try (InputStream inputStream = new FileInputStream(file); OutputStream os = fileItem.getOutputStream()){
            while ( (n = inputStream.read(buffer,0,4096)) != -1){
                os.write(buffer,0,n);
            }
            //也可以用IOUtils.copy(inputStream,os);
            MultipartFile multipartFile = new CommonsMultipartFile(fileItem);
            System.out.println(multipartFile.getName());
            return multipartFile;
        }catch (IOException e){
            e.printStackTrace();
        }
        return null;
    }