將 JSON 響應序列化為 Java Object 時出現問題

Question

我是 Java 的新手。 I am trying to serialize a JSON response into a Java Object (UserData) but i am having some issues with the empty and null fields (even, i do not know the type of part of this data).

JSON 響應如下：

    "id": 88,
    "username": "palomajim",
    "name": "Paloma Jimeno",
    "language": "en",
    "height": null,
    "isActive": true,
    "statistics": null,
    "tablets": [],
    "category": null,
    "role": null,
    "senior": [],
    "projects": null
}

如您所見，null 和空列表字段太多。 我對創建一個 Java Object 很感興趣，它只考慮“id”、“用戶名”、“名稱”、“語言”和“isActive”字段，忽略空列表和 Z37A6259CC0C1DAE299ZBDBD48DBD48666666。

目前，我的客戶 class 如下：

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.client.RestTemplate;
 
@SpringBootApplication
public class RESTClient {

    static final String URL_NLP = "https://xxx/senior?by_senior_id=";
 
    public UserData getUserData(String idUser) {
 
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.set("x-api-key", "xxx");

        HttpEntity<User> entity = new HttpEntity<User>(headers);

        // RestTemplate
        RestTemplate restTemplate = new RestTemplate();

        // Send request with GET method, and Headers.
        ResponseEntity<UserData> response = restTemplate.exchange(URL_NLP+idUser, HttpMethod.GET, entity, UserData.class);

        HttpStatus statusCode = response.getStatusCode();
        System.out.println("Response Satus Code: " + statusCode);
 
        // Status Code: 200
        if (statusCode != HttpStatus.OK) {
            return null;     
        }

        // Response Body Data
        UserData u = response.getBody();
            
        System.out.println("User name: " + u.getName());

        return u;

    }

而代表UserData的class（object序列化JSON響應中的信息如下）：

import java.io.Serializable;
import java.util.List;
import java.util.Objects;

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonInclude;

@JsonInclude(JsonInclude.Include.NON_NULL)
public class UserData implements Serializable {

    private Integer id;
    private String username;
    private String name;
    private String language;
    private Boolean isActive;
    

    public UserData() {
    }

    public UserData(Integer id, String username, String name, String language) {
        this.id = id;
        this.username = username;
        this.name = name;
        this.language = language;

    }

    public Integer get_id() {
        return this.id;
    }

    public void set_id(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return this.username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getLanguage() {
        return this.language;
    }

    public void setLanguage(String language) {
        this.language = language;
    }

    public boolean getIsActive(){return this.isActive; }

    public void setIsActive(){this.isActive = isActive;}

    public UserData id(Integer id) {
        this.id = id;
        return this;
    }

    public UserData username(String username) {
        this.username = username;
        return this;
    }

    public UserData name(String name) {
        this.name = name;
        return this;
    }

    public UserData language(String language) {
        this.language = language;
        return this;
    }


    @Override
    public boolean equals(Object o) {
        if (o == this)
            return true;
        if (!(o instanceof UserData)) {
            return false;
        }
        UserData userData = (UserData) o;
        boolean b = Objects.equals(id, userData.id) && Objects.equals(name, userData.name)
                && Objects.equals(username, userData.username) && Objects.equals(language, userData.language) ;
        return Objects.equals(id, userData.id) && Objects.equals(name, userData.name) && Objects.equals(username, userData.username)
                && Objects.equals(language, userData.language);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, username, name, language);
    }

    @Override
    public String toString() {
        return "{" +
            " id='" + get_id().toString() + "'" +
            ", username='" + getUsername() + "'" +
            ", name='" + getName() + "'" +
            ", language='" + getLanguage() + "'" +
            ", isActive='" + "" + "'" +
            "}";
    }
}

但是，我在 RESTClient class 中收到以下錯誤。

Method threw 'java.lang.NullPointerException' exception. Cannot evaluate org.springframework.http.ResponseEntity.toString()

你知道我做錯了什么嗎？ 我應該在 UserData class 中以另一種方式進行嗎？ 我不知道 null 字段和空列表的類型，因此無法在 UserData class 的構造函數中考慮它們。 你可以幫幫我嗎？

Answer 1

該異常不言自明，您在 toString 方法中有一個 null 指針異常。 連接字符串時無需在 Integer 上使用 a.toString() ，您可以像這樣更改 toString() 方法：

@Override
public String toString() {
    return "{" +
        " id='" + get_id() + "'" +
        ", username='" + getUsername() + "'" +
        ", name='" + getName() + "'" +
        ", language='" + getLanguage() + "'" +
        ", isActive='" + "" + "'" +
        "}";
}

如果我們正在談論而不是更復雜的 object，為了避免 null 指針使用String.valueOf(object) 。 如果 object 是 null，則此特定方法將打印“null”，並且如果不是 objectC4B666F8911C4B6666C4BD37A6ZDAE290C18DFF07A6Z866C40