改型不会在Android的PHP后端上提供Java对象作为POST参数

$_POST

public class RetrofitClient {

    private static Retrofit retrofit;
    private static final String BASE_URL = "http://www.example.com";

    public static Retrofit getInstance() {
        if (retrofit == null) {
            retrofit = new retrofit2.Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit;
    }
}

2) 正在发送的参数的模型

public class LoginModel {

    @SerializedName("email")
    private String email;

    @SerializedName("password")
    private String password;

    public LoginModel(String email, String password) {
        this.email = email;
        this.password = password;
    }

    public String getEmail() { return email; }
    public String getPassword() { return password; }
}

public interface RequestAPI {

    @POST("/login")
    Call<ResponseBody> getResponse(@Body LoginModel loginModel) ;
}

@Override
public void onClick(View v) {

    LoginModel loginModel = new LoginModel("user@example.com", "123");

    RequestAPI service = RetrofitClient.getInstance().create(RequestAPI.class);

    Call<ResponseBody> call = service.getResponse(loginModel);

    call.enqueue(new Callback<ResponseBody>() {

        @Override
        public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
            try {
                Log.e("=====", response.body().string());
            }catch (Exception e){
                e.printStackTrace();
            }
        }

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

echo json_encode($_POST);

现在每次我转储$\u POST变量时。它只是给了一个 .

为什么我没有收到 电子邮件 和 密码 作为$邮政的孩子?