改造 - 多部分请求：所需的 MultipartFile 参数“文件”不存在

我正在尝试使用 Retrofit2 在服务器上发送文件。 我按照文档做了一切，但总是收到 400 服务器错误。

我尝试这样做：

RequestBody body =
                RequestBody.create(MediaType.parse("image/png"), photo);
    //..........

    @Multipart
    @POST(ADD_PHOTO)
    Observable<HPSPhotoResponse>
    addPhoto(@Part("file") RequestBody file);

...就像这样：

MultipartBody.Part part = MultipartBody.Part.createFormData("file", "file", body);
     //...........

    @Multipart
    @POST(ADD_PHOTO)
    Observable<HPSPhotoResponse>
    addPhoto(@Part("file") MultipartBody.Part files);

没关系。结果始终相同“Multipart 请求：所需的 MultipartFile 参数‘文件’不存在”- 服务器响应。

我认为服务器上的 Spring 工作得不好，但我在 Swift (iOS) 上做了等效的代码并且它工作了！服务器在这里看到这个“文件”部分。

Alamofire.upload(method, endpoint, headers: headers,
            multipartFormData: { multipartFormData in
                multipartFormData.appendBodyPart(fileURL: self.filePath!, name: "file")
            }

现在我希望它可以通过 Retrofit 在 Android 上运行。 但我什至查看了改造请求的日志，实际上我在日志中没有看到任何“文件”文本。

这有什么问题吗？

您可以尝试以下示例代码。在此演示应用程序中，我们将从图库中选择照片后上传照片。希望能帮助到你！

构建.gradle file:

dependencies {
    ...
    compile 'com.squareup.retrofit2:retrofit:2.0.1'
    compile 'com.squareup.retrofit2:converter-gson:2.0.1'
    ...
}

WebAPIService.java file:

public interface WebAPIService {

    @Multipart
    @POST("/api/fileupload")
    Call<ResponseBody> postFile(@Part MultipartBody.Part file, @Part("description") RequestBody description);
}

文件活动.java file:

...
import okhttp3.MediaType;
import okhttp3.MultipartBody;
import okhttp3.RequestBody;
import okhttp3.ResponseBody;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;

public class FileActivity extends AppCompatActivity {

    private final Context mContext = this;
    private final String API_URL_BASE = "http://serverip:port";
    private final String LOG_TAG = "BNK";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_file);

        selectImage(); // selects a photo from Gallery
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (resultCode == Activity.RESULT_OK && requestCode == 100) {
            Uri fileUri = data.getData();
            if (fileUri != null) {
                uploadFile(fileUri); // uploads the file to the web service
            }
        }
    }

    private void uploadFile(Uri fileUri) {

        String filePath = getRealPathFromUri(fileUri);
        if (filePath != null && !filePath.isEmpty()) {
            File file = new File(filePath);
            if (file.exists()) {
                Retrofit retrofit = new Retrofit.Builder()
                        .baseUrl(API_URL_BASE)
                        .build();

                WebAPIService service = retrofit.create(WebAPIService.class);

                // creates RequestBody instance from file
                RequestBody requestFile = RequestBody.create(MediaType.parse("multipart/form-data"), file);
                // MultipartBody.Part is used to send also the actual filename
                MultipartBody.Part body = MultipartBody.Part.createFormData("file", file.getName(), requestFile);
                // adds another part within the multipart request
                String descriptionString = "Sample description";
                RequestBody description = RequestBody.create(MediaType.parse("multipart/form-data"), descriptionString);
                // executes the request
                Call<ResponseBody> call = service.postFile(body, description);                
                call.enqueue(new Callback<ResponseBody>() {
                    @Override
                    public void onResponse(Call<ResponseBody> call,
                                           Response<ResponseBody> response) {
                        Log.i(LOG_TAG, "success");
                    }

                    @Override
                    public void onFailure(Call<ResponseBody> call, Throwable t) {
                        Log.e(LOG_TAG, t.getMessage());
                    }
                });
            }
        }
    }

    private void selectImage() {
        Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
        intent.setType("image/*");
        startActivityForResult(intent, 100);
    }

    public String getRealPathFromUri(final Uri uri) {
        // DocumentProvider
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT && DocumentsContract.isDocumentUri(mContext, uri)) {
            // ExternalStorageProvider
            if (isExternalStorageDocument(uri)) {
                final String docId = DocumentsContract.getDocumentId(uri);
                final String[] split = docId.split(":");
                final String type = split[0];

                if ("primary".equalsIgnoreCase(type)) {
                    return Environment.getExternalStorageDirectory() + "/" + split[1];
                }
            }
            // DownloadsProvider
            else if (isDownloadsDocument(uri)) {

                final String id = DocumentsContract.getDocumentId(uri);
                final Uri contentUri = ContentUris.withAppendedId(
                        Uri.parse("content://downloads/public_downloads"), Long.valueOf(id));

                return getDataColumn(mContext, contentUri, null, null);
            }
            // MediaProvider
            else if (isMediaDocument(uri)) {
                final String docId = DocumentsContract.getDocumentId(uri);
                final String[] split = docId.split(":");
                final String type = split[0];

                Uri contentUri = null;
                if ("image".equals(type)) {
                    contentUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
                } else if ("video".equals(type)) {
                    contentUri = MediaStore.Video.Media.EXTERNAL_CONTENT_URI;
                } else if ("audio".equals(type)) {
                    contentUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
                }

                final String selection = "_id=?";
                final String[] selectionArgs = new String[]{
                        split[1]
                };

                return getDataColumn(mContext, contentUri, selection, selectionArgs);
            }
        }
        // MediaStore (and general)
        else if ("content".equalsIgnoreCase(uri.getScheme())) {

            // Return the remote address
            if (isGooglePhotosUri(uri))
                return uri.getLastPathSegment();

            return getDataColumn(mContext, uri, null, null);
        }
        // File
        else if ("file".equalsIgnoreCase(uri.getScheme())) {
            return uri.getPath();
        }

        return null;
    }

    private String getDataColumn(Context context, Uri uri, String selection,
                                        String[] selectionArgs) {

        Cursor cursor = null;
        final String column = "_data";
        final String[] projection = {
                column
        };

        try {
            cursor = context.getContentResolver().query(uri, projection, selection, selectionArgs,
                    null);
            if (cursor != null && cursor.moveToFirst()) {
                final int index = cursor.getColumnIndexOrThrow(column);
                return cursor.getString(index);
            }
        } finally {
            if (cursor != null)
                cursor.close();
        }
        return null;
    }

    private boolean isExternalStorageDocument(Uri uri) {
        return "com.android.externalstorage.documents".equals(uri.getAuthority());
    }

    private boolean isDownloadsDocument(Uri uri) {
        return "com.android.providers.downloads.documents".equals(uri.getAuthority());
    }

    private boolean isMediaDocument(Uri uri) {
        return "com.android.providers.media.documents".equals(uri.getAuthority());
    }

    private boolean isGooglePhotosUri(Uri uri) {
        return "com.google.android.apps.photos.content".equals(uri.getAuthority());
    }
}