添加权限

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

添加依赖

implementation("com.squareup.okhttp3:okhttp:3.12.3")

示例代码

/**
 * Okhttp上传图片(流)
 */
private void okHttpUploadImage() {
    // 创建 OkHttpClient
    OkHttpClient client = new OkHttpClient.Builder().build();
    // 要上传的文件
    File file = new File("/storage/emulated/0/Download/timg-4.jpg");
    MediaType mediaType = MediaType.parse("image/jpeg");
    // 把文件封装进请求体
    RequestBody fileBody = RequestBody.create(mediaType, file);
    // MultipartBody 上传文件专用的请求体
    RequestBody body = new MultipartBody.Builder()
            .setType(MultipartBody.FORM) // 表单类型(必填)
            .addFormDataPart("smfile", file.getName(), fileBody)
            .build();
    Request request = new Request.Builder()
            .url("https://sm.ms/api/upload")
            .header("User-Agent", "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:66.0) Gecko/20100101 Firefox/66.0")
            .post(body)
            .build();
    Call call = client.newCall(request);
    call.enqueue(new Callback() {

        @Override
        public void onResponse(Call call, Response response) throws IOException {
            if (response.isSuccessful()) {
                System.out.println(response.body().string());
            } else {
                System.out.println(response.code());
            }
        }

        @Override
        public void onFailure(Call call, IOException e) {
            System.out.println(e.getMessage());
        }
    });
}