//参数类型
private static final MediaType MEDIA_TYPE_PNG = MediaType.parse("image/png");
//创建OkHttpClient实例
private final OkHttpClient client = new OkHttpClient();
MultipartBuilder builder = new MultipartBuilder().type(MultipartBuilder.FORM);
//遍历map中所有参数到builder
for (String key : map.keySet()) {
      builder.addFormDataPart(key, map.get(key));
    }
  //遍历paths中所有图片绝对路径到builder，并约定key如“upload”作为后台接受多张图片的key
    for (String path : paths) {
      builder.addFormDataPart("upload", null, RequestBody.create(MEDIA_TYPE_PNG, new File(path)));
    }
   //构建请求体
    RequestBody requestBody = builder.build();
 //构建请求
 Request request = new Request.Builder()
        .url(url)//地址
        .post(requestBody)//添加请求体
        .build(); 
//发送异步请求，同步会报错，Android4.0以后禁止在主线程中进行耗时操作
client.newCall(request).enqueue(new Callback() {
      @Override
      public void onFailure(Request request, IOException e) {
        System.out.println("request = " + request.urlString());
        System.out.println("e.getLocalizedMessage() = " + e.getLocalizedMessage())；
      }
      @Override
      public void onResponse(Response response) throws IOException {
        //看清楚是response.body().string()不是response.body().toString()
             System.out.println("response = " + response.body().string());
             }
    });