如何在Android中利用OkHttp与php实现一个图片上传功能

public class MainActivity extends AppCompatActivity {  private OkHttpClient client;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    client = new OkHttpClient();    postImage();  }  private void postImage(){    //这里方便演示。读取drawable里的图片。    Bitmap bm = BitmapFactory.decodeResource(getResources(),R.drawable.demo);    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();    bm.compress(Bitmap.CompressFormat.JPEG,100,byteArrayOutputStream);    MultipartBody.Builder builder = new MultipartBody.Builder().setType(MultipartBody.FORM)        .addFormDataPart("img_1","1.jpg", RequestBody.create(MediaType.parse("image/jpeg"),byteArrayOutputStream.toByteArray()))        .addFormDataPart("img_2","2.jpg", RequestBody.create(MediaType.parse("image/jpeg"),byteArrayOutputStream.toByteArray()))        ;    //有多个图片就用for循环添加即可    MultipartBody build = builder.build();    okhttp3.Request bi = new okhttp3.Request.Builder()        .url("后台地址")         .post(build)        .build();    client.newCall(bi).enqueue(new Callback() {      @Override      public void onFailure(Call call, IOException e) {        Log.i("TAG", "onFailure: 失败");      }      @Override      public void onResponse(Call call, okhttp3.Response response) throws IOException {        Log.i("TAG", "onResponse: " + response.body().string());        //提交成功处理结果....      }    });  }}