SpringBoot +Flutter + Dio + multi_image_picker +MultipartFile实现多文件上传

Flutter部分

图片上传部分UI

IconButton(
 onPressed: loadAssets,
  icon: Icon(Icons.photo),
),

加载资源

Future loadAssets() async {
    List resultList = List();
    String error = 'No Error Dectected';
    try {
      resultList = await MultiImagePicker.pickImages(
        maxImages: 9,
        enableCamera: true,
        selectedAssets: images,
        cupertinoOptions: CupertinoOptions(takePhotoIcon: "chat"),
        materialOptions: MaterialOptions(
            actionBarColor: "#abcdef",
            actionBarTitle: "Example App",
            allViewTitle: "All Photos",
            useDetailsView: false,
            selectCircleStrokeColor: "#000000",
            startInAllView: true),
      );
    } on Exception catch (e) {
      error = e.toString();
    }
    if (!mounted) return;

    setState(() {
      images = resultList;
      _error = error;
    });
  }

点击发布按钮，将图片上传到SpringBoot

RaisedButton(
    color: Colors.green,
    child: Text(
      '发布',
      style: TextStyle(color: Colors.white, fontSize: 17),
    ),
    onPressed: uploadImageToServer
),

上传图片方法

  // 上传图片数据到Springboot后台
  uploadImageToServer() async {
    List imageList = new List();
    String url = "http://192.168.0.105:8989/users/user/testSend";
    for (Asset asset in images) {
      ByteData byteData = await asset.getByteData();
      List imageData = byteData.buffer.asUint8List();
      MultipartFile multipartFile = new MultipartFile.fromBytes(
        imageData,
        filename: 'load_image',
        contentType: MediaType("image", "jpg"),
      );
      imageList.add(multipartFile);
      // print("图片数据：$imageData");
    }
    print("图片数量:${imageList.length}");

    FormData formData = FormData.fromMap({
      "multipartFiles": imageList,
      "test" : "test",
    });

    Dio dio = new Dio();
    var response = await dio.post(url, data: formData);

    //响应处理
    if (response.data["success"]) {
      print(response.data);
      Fluttertoast.showToast(
        msg: "博客上传成功，等待审核",
        gravity: ToastGravity.CENTER,
        textColor: Colors.grey,
      );
    } else {
      Fluttertoast.showToast(
        msg: "博客上传失败，请稍后再试",
        gravity: ToastGravity.CENTER,
        textColor: Colors.grey,
      );
    }
  }

在这个地方卡了挺久的，不知道什么原因，上传到SpringBoot的时候，Springboot一直显示无法接收到图片数据。在网上查了很多资料，都大同小异，没办法解决。最后想到的是用WireShark来抓包，查看上传到SpringBoot的参数是什么。看下图，注意这个参数。接下来看看SpringBoot接收参数。

SpringBoot部分，接收来自Flutter的图片数据

@PostMapping("testSend")
    public Map<String, Object> testSend(@RequestParam("multipartFiles[]") List<MultipartFile> multipartFiles, @RequestParam("test") String test) throws IOException {
//        List multipartFiles1 = ((MultipartHttpServletRequest) request).getFiles("multipartFiles");
        System.out.println("requestParam:"+multipartFiles.size());
        System.out.println("test:"+test);
//        System.out.println("files:" + files.length);
        for (MultipartFile multipartFile :
                multipartFiles) {
            BufferedImage image = ImageIO.read(multipartFile.getInputStream());

            String extention ="."+ multipartFile.getContentType().split("/")[1];
            UUID uuid = UUID.randomUUID();
            String path = "D:/desktop/" + uuid+ extention;
            File outputFile = new File(path);
            ImageIO.write(image,"jpg",outputFile);
        }

        Map<String, Object> map = new HashMap<>();
        map.put("success",true);
        return map;
    }

这部分需要特别注意的就是这个注解@RequestParam(“multipartFiles[]”)，我们看之前在Flutter 的FormData里面设置的是multipartFiles，而这里必须设置为multipartFiles[]，否则无法获取到传递过来的图片数据

在此之前，为了排查是前端错误还是后端错误，用过PostMan上传图片数据，显示是能上传成功的，所以就认为可能错误是出现在Flutter那里（实际上不是，就是在SpringBoot！！！）。