谢谢您的建议，但我想出了一种可行的方法。这是我的方法…

首先，在我的Pojo课堂上，我添加了一个JsonDeserializer，然后检查“数据”是对象还是基元，并据此设置相应的字段。

public class UserResponse  {

    @SerializedName("status")
    private String status;
    @SerializedName("data")
    private Object mData;
    @SerializedName("response")
    private String response;
    @SerializedName("error")
    private String error;

    private String message;
    private String firstname;
    private String lastname;
    private String mobilenumber;
    private String emailid;
    private String timezone;

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public String getFirstname() {
        return firstname;
    }

    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }

    public String getLastname() {
        return lastname;
    }

    public void setLastname(String lastname) {
        this.lastname = lastname;
    }

    public String getMobilenumber() {
        return mobilenumber;
    }

    public void setMobilenumber(String mobilenumber) {
        this.mobilenumber = mobilenumber;
    }

    public String getEmailid() {
        return emailid;
    }

    public void setEmailid(String emailid) {
        this.emailid = emailid;
    }

    public String getTimezone() {
        return timezone;
    }

    public void setTimezone(String timezone) {
        this.timezone = timezone;
    }

    public String getStatus() {
        return status;
    }

    public void setStatus(String status) {
        this.status = status;
    }

    public Object getmData() {
        return mData;
    }

    public String getResponse() {
        return response;
    }

    public String getError() {
        return error;
    }

    public static class DataStateDeserializer implements JsonDeserializer<UserResponse> {

        @Override
        public UserResponse deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
            UserResponse userResponse = new Gson().fromJson(json, UserResponse.class);
            JsonObject jsonObject = json.getAsJsonObject();

            if (jsonObject.has("data")) {
                JsonElement elem = jsonObject.get("data");
                if (elem != null && !elem.isJsonNull()) {                     
                    if(elem.isJsonPrimitive()){                            
                        userResponse.setMessage(elem.getAsString());
                    }else{

                        userResponse.setFirstname(elem.getAsJsonObject().get("firstname").getAsString());
                        userResponse.setLastname(elem.getAsJsonObject().get("lastname").getAsString());
                        userResponse.setMobilenumber(elem.getAsJsonObject().get("mobilenumber").getAsString());
                        userResponse.setEmailid(elem.getAsJsonObject().get("emailid").getAsString());
                        userResponse.setTimezone(elem.getAsJsonObject().get("timezone").getAsString());
                    }
                }
            }
            return userResponse ;
        }
    }
}

然后将json解串器附加到GSON Builder的类型适配器，并像这样在Retrofit中给它创建GsonConvertor的方法

Gson gson = new GsonBuilder()
                 .registerTypeAdapter(UserResponse.class, new UserResponse.DataStateDeserializer())
                .create();

Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(ConstantUtils.BASE_URL)
                .addConverterFactory(GsonConverterFactory.create(gson))
                .build();

UserInfoRequestInterface requestInterface = retrofit.create(UserInfoRequestInterface.class);
        Call<UserResponse> call = requestInterface.getInfoUpdated(user_id, firstName, lastName, phoneNumber, email, null, null);

然后，我要做的就是检查message是否为null并相应地执行所需的操作。