Gson反序列化静态字段为null的解析与解决方案

{
  "date": "2022-12-08",
  "explanation": "...",
  "hdurl": "https://apod.nasa.gov/apod/image/2212/art001e002132.jpg",
  "media_type": "image",
  "service_version": "v1",
  "title": "Orion and the Ocean of Storms",
  "url": "https://apod.nasa.gov/apod/image/2212/art001e002132_apod1024.jpg"
}

package space;

import com.google.gson.Gson;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.net.http.HttpResponse.BodyHandlers;

public class Output {

    public static void main(String[] args) throws IOException, InterruptedException, URISyntaxException {
        // 假设这里获取到JSON字符串
        String jsonResponse = "{\n" +
                "  \"date\": \"2022-12-08\",\n" +
                "  \"explanation\": \"A camera on board the uncrewed Orion spacecraft captured this view on December 5 as Orion approached its return powered flyby of the Moon.  Below one of Orion's extended solar arrays lies dark, smooth, terrain along the western edge of the Oceanus Procellarum. Prominent on the lunar nearside Oceanus Procellarum, the Ocean of Storms, is the largest of the Moon's lava-flooded maria. The lunar terminator, shadow line between lunar night and day, runs along the left of the frame. The 41 kilometer diameter crater Marius is top center, with ray crater Kepler peeking in at the edge, just right of the solar array wing. Kepler's bright rays extend to the north and west, reaching the dark-floored Marius. Of course the Orion spacecraft is now headed toward a December 11 splashdown in planet Earth's water-flooded Pacific Ocean.\",\n" +
                "  \"hdurl\": \"https://apod.nasa.gov/apod/image/2212/art001e002132.jpg\",\n" +
                "  \"media_type\": \"image\",\n" +
                "  \"service_version\": \"v1\",\n" +
                "  \"title\": \"Orion and the Ocean of Storms\",\n" +
                "  \"url\": \"https://apod.nasa.gov/apod/image/2212/art001e002132_apod1024.jpg\"\n" +
                "}";

        Gson gson = new Gson();
        // 假设Objects是用于映射JSON的POJO类
        Objects nasaObject = gson.fromJson(jsonResponse, Objects.class);
        String resultUrl = nasaObject.getUrl(); // 获取反序列化后的url
        System.out.println("反序列化后的URL: " + resultUrl);
    }
}

package space;

public class Objects {
    private static String url; // 错误：字段被声明为静态

    public static String getUrl() { // 静态getter
        return url;
    }
    // 即使有setter，如果字段是静态的，Gson也可能无法正确处理
    public void setUrl(String url) {
        Objects.url = url;
    }
}

package space;

public class Objects {
    private String url; // 正确：字段为非静态实例字段
    private String hdurl; // 如果需要获取hdurl，也应定义为非静态字段
    private String title; // 其他字段同理

    // 默认构造函数是必需的，即使是空的
    public Objects() {
    }

    // Getter方法
    public String getUrl() {
        return url;
    }

    // Setter方法（可选，Gson可以通过反射直接设置字段）
    public void setUrl(String url) {
        this.url = url;
    }

    public String getHdurl() {
        return hdurl;
    }

    public void setHdurl(String hdurl) {
        this.hdurl = hdurl;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }
}