在gradle中使用这些

compile 'com.squareup.retrofit2:retrofit:2.3.0'
compile 'com.squareup.retrofit2:converter-gson:2.3.0'
compile 'com.squareup.retrofit2:converter-scalars:2.3.0'

使用这两个POJO类……
LoginData.class

public class LoginData {

    private String email;
    private String password;

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

    /**
     *
     * @return
     * The email
     */
    public String getEmail() {
        return email;
    }

    /**
     *
     * @param email
     * The email
     */
    public void setEmail(String email) {
        this.email = email;
    }

    /**
     *
     * @return
     * The password
     */
    public String getPassword() {
        return password;
    }

    /**
     *
     * @param password
     * The password
     */
    public void setPassword(String password) {
        this.password = password;
    }

}

LoginResult.class

public class LoginResult {

    private Boolean error;
    private String message;
    private Integer doctorid;
    private Boolean active;

    /**
     *
     * @return
     * The error
     */
    public Boolean getError() {
        return error;
    }

    /**
     *
     * @param error
     * The error
     */
    public void setError(Boolean error) {
        this.error = error;
    }

    /**
     *
     * @return
     * The message
     */
    public String getMessage() {
        return message;
    }

    /**
     *
     * @param message
     * The message
     */
    public void setMessage(String message) {
        this.message = message;
    }

    /**
     *
     * @return
     * The doctorid
     */
    public Integer getDoctorid() {
        return doctorid;
    }

    /**
     *
     * @param doctorid
     * The doctorid
     */
    public void setDoctorid(Integer doctorid) {
        this.doctorid = doctorid;
    }

    /**
     *
     * @return
     * The active
     */
    public Boolean getActive() {
        return active;
    }

    /**
     *
     * @param active
     * The active
     */
    public void setActive(Boolean active) {
        this.active = active;
    }

}

像这样使用API

public interface RetrofitInterface {
     @POST("User/DoctorLogin")
        Call<LoginResult> getStringScalar(@Body LoginData body);
}

这样调用...

Retrofit retrofit = new Retrofit.Builder()
            .baseUrl("Your domain URL here")
            .addConverterFactory(ScalarsConverterFactory.create())
            .addConverterFactory(GsonConverterFactory.create())
            .build();

       RetrofitInterface service = retrofit.create(RetrofitInterface .class);

 Call<LoginResult> call=service.getStringScalar(new LoginData(email,password));
    call.enqueue(new Callback<LoginResult>() {
                @Override
                public void onResponse(Call<LoginResult> call, Response<LoginResult> response) { 
               //response.body() have your LoginResult fields and methods  (example you have to access error then try like this response.body().getError() )

              }

                @Override
                public void onFailure(Call<LoginResult> call, Throwable t) {
           //for getting error in network put here Toast, so get the error on network 
                }
            });

编辑：-

把这个放进success()里面....

if(response.body().getError()){
   Toast.makeText(getBaseContext(),response.body().getMessage(),Toast.LENGTH_SHORT).show();

}else {
          //response.body() have your LoginResult fields and methods  (example you have to access error then try like this response.body().getError() )
                String msg = response.body().getMessage();
                int docId = response.body().getDoctorid();
                boolean error = response.body().getError();  

                boolean activie = response.body().getActive()();   
}

注意：-始终使用POJO类，它删除了改造中的JSON数据解析。

这条路适合我
我的Web服务

把这个加到你的gradle里

compile 'com.squareup.retrofit2:retrofit:2.3.0'
compile 'com.squareup.retrofit2:converter-gson:2.3.0'
compile 'com.squareup.retrofit2:converter-scalars:2.3.0'

接口

public interface ApiInterface {

    String ENDPOINT = "http://10.157.102.22/rest/";

    @Headers("Content-Type: application/json")
    @POST("login")
    Call<User> getUser(@Body String body);

}

活动

public class SampleActivity extends AppCompatActivity implements Callback<User> {

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sample);

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(ApiInterface.ENDPOINT)
                .addConverterFactory(ScalarsConverterFactory.create())
                .addConverterFactory(GsonConverterFactory.create())
                .build();

        ApiInterface apiInterface = retrofit.create(ApiInterface.class);

        // prepare call in Retrofit 2.0
        try {
            JSONObject paramObject = new JSONObject();
            paramObject.put("email", "[email protected]");
            paramObject.put("pass", "4384984938943");

            Call<User> userCall = apiInterface.getUser(paramObject.toString());
            userCall.enqueue(this);
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onResponse(Call<User> call, Response<User> response) {
    }

    @Override
    public void onFailure(Call<User> call, Throwable t) {
    }
}

我认为您现在应该创建一个服务生成器类，然后使用Call调用您的服务

PostInterface postInterface = ServiceGenerator.createService(PostInterface.class);
Call<responseBody> responseCall =
            postInterface.getStringScalar(requestBody);

然后你可以使用它来同步请求并获得响应的主体：

responseCall.execute().body();

对于异步：

responseCall.enqueue(Callback);

有关完整的演练以及如何创建ServiceGenerator，请参阅下面提供的链接：
https://futurestud.io/tutorials/retrofit-getting-started-and-android-client

从Retrofit 2+开始，使用POJO对象而不是JSON对象来发送带有@Body注解的请求。随着JSON对象被发送，请求字段被设置为它们的默认值，而不是从后端的应用程序发送的值。POJO对象则不是这种情况。

1. JSON在Post Request中

val jsonObject = JSONObject()
            try {
                jsonObject.put("name", name)
                jsonObject.put("username", username)
                jsonObject.put("email", email)
                jsonObject.put("phone", phone)
                jsonObject.put(
                    "token",
                    Prefs.getPrefInstance()!!.getValue(requireContext(), Const.TOKEN, "")
                )
                //                jsonObject.put("image", uploaded_image);
                jsonObject.put("image", url)
            } catch (e: JSONException) {
                binding.loader.visibility = View.GONE
                e.printStackTrace()
            }
            val params = jsonObject.toString()
            val user_registering = params.toRequestBody("application/json".toMediaTypeOrNull())