Ionic3多部分表单图像上传

Question

我想将多部分表单数据上传到restapi，在Postman客户端上请求时api正常工作。

这是我的代码：

takePhoto() {  
  const options: CameraOptions = {  
    quality: 100,  
    allowEdit: true,  
    targetWidth: 200,  
    targetHeight: 200,  
    saveToPhotoAlbum: true,  
    encodingType: this.camera.EncodingType.JPEG,  
    mediaType: this.camera.MediaType.PICTURE 
  };  

  this.camera.getPicture(options).then(image => {  
    console.log('Image URI: ' + image);  
     this.image_File = image;  
     this.imgfile = this.imageURI;  
    console.log(JSON.stringify(this.imageURI));  
    this.avatar = image.slice(7);  
    this.imgfile = this.avatar;  
  }, error => { 
    console.log('Error: ' + error);  
  });
}  

为上传文件，我定义了一个函数：

console.log("begin to upload ");  
let link = rootUrl+"merchant/merchant-image";  
let data = new FormData();  
// var blob = new Blob([this.image_File], { type: "image/jpg" });  
data.append('merchantId', '2');  
data.append('merchantImage',this.imgfile);  

console.log(data);  
this.http.post(link, data,{ 
  headers:{  
    "Accept-Language":this.lang,  
    //'enctype': 'multipart/form-data',  
   // 'Content-Type': 'multipart/form-data',  
  } 
}).subscribe(data2 => {   
  console.log("data Successful "+ data2);  
}, error => {   
  console.log("Oooops! error "+ JSON.stringify(error));  
});    

来自服务器的响应：

{ 
  "headers": {
    "normalizedNames": {},
    "lazyUpdate": null
  },
  "status": 400,
  "statusText": "OK",
  "url": "http://xxxxxxxxxxx/merchant/merchant-image",
  "ok": false,
  "name": "HttpErrorResponse",
  "message": "Http failure response for http://xxxxxxxxxxxxx/merchant/merchant-image: 400 OK",
  "error": {
    "timestamp": "2018-08-14T10:13:14.693+0000",
    "status": 400,
    "error": "Bad Request",
    "message": "Required request part 'merchantImage' is not present",
    "path": "/api/v1/merchant/merchant-image"
  }
}