Okhttp上传图片

public static void Imger(String url,File file,String filename,Map<String,String> params,Callback callback){
    OkHttpClient instance = getInstance();
    MultipartBody.Builder builder=new MultipartBody.Builder();
    if (params == null) {
        for (String in:params.keySet()) {
            builder.addFormDataPart(in,params.get(in));
        }
    }
    builder.setType(MultipartBody.FORM);
    builder.addFormDataPart("file",filename, RequestBody.create(MediaType.parse("application/octet-stream"),file));
    Request request=new Request.Builder()
            .url(url)
            .post(builder.build())
            .build();
    instance.newCall(request).enqueue(callback);
}