文件上传（不生成临时文件）

• 背景

  1. 有两个服务，A服务有一个文件上传的接口，B服务通过restTemplate调用A服务的接口上传一个文件。
  2. B服务已经拿到文件内容。那么是否能够在不需要生成临时文件的情况下上传文件到A服务呢？

• 实现过程

  1. 定义内容

     String fileStr = "文件内容";

  2. 字符串转换成byte[]

         byte[] xmlBytes = fileStr.getBytes();

  3. 自定义MultipartFile实现类

     public class BASE64DecodedMultipartFile implements MultipartFile {
         // 上传文件字节流
         private final byte[] imgContent;
         // 上传文件的文件名
         private final String originalFilename;
     
         public BASE64DecodedMultipartFile(byte[] imgContent, String originalFilename) {
             this.imgContent = imgContent;
             this.originalFilename = originalFilename;
         }
     
         @Override
         public String getName() {
             // TODO - implementation depends on your requirements
             return null;
         }
     
         @Override
         public String getOriginalFilename() {
             // TODO - implementation depends on your requirements
             return this.originalFilename;
         }
     
         @Override
         public String getContentType() {
             // TODO - implementation depends on your requirements
             return null;
         }
     
         @Override
         public boolean isEmpty() {
             return imgContent == null || imgContent.length == 0;
         }
     
         @Override
         public long getSize() {
             return imgContent.length;
         }
     
         @Override
         public byte[] getBytes() throws IOException {
             return imgContent;
         }
     
         @Override
         public InputStream getInputStream() throws IOException {
             return new ByteArrayInputStream(imgContent);
         }
     
         @Override
         public void transferTo(File dest) throws IOException, IllegalStateException {
             new FileOutputStream(dest).write(imgContent);
         }
     }

  4. 构造上传文件对象

     MultipartFile mf = new BASE64DecodedMultipartFile(xmlBytes, fileName);

  5. 通过restTemplate调用远程接口

     HttpHeaders headers = new HttpHeaders();
     headers.setContentType(MediaType.MULTIPART_FORM_DATA);
     MultiValueMap<String, Object> requestparams = new LinkedMultiValueMap<>();
     requestparams.add("file", mf.getResource());
     requestparams.add("filename", mf.getOriginalFilename());
     HttpEntity<MultiValueMap<String, Object>> requestEntity = new HttpEntity<>(requestparams, headers);
     RestTemplate restTemplate = new RestTemplate();
     Object resultVo = restTemplate.postForObject(url, requestEntity, Object.class);