场景：

public class TestUtil {
    @Autowired
    private static MiniAppService staticMiniAppService;

    public static void test() {
        staticMiniAppService.getById(1);
    }
}

这样会报java.lang.NullPointerException: null异常
原因：
静态方法属于类，静态变量是类的属性，Spring注入需要实例化对象，所以不能使用静态方法

方案1
使用@Component和@PostConstruct实现静态类加载Spring自动注入

@Component
public class TestUtil {
    @Autowired
    private static MiniAppService staticMiniAppService;

    @Autowired
    private MiniAppService miniAppService;

    @PostConstruct
    public void init() {
        staticMiniAppService = miniAppService;
    }

    public static void test() {
        staticMiniAppService.getById(1);
    }
}

方案二
@Autowire加到构造方法上

@Component
public class TestUtil {
   
    private static MiniAppService staticMiniAppService;

   @Autowired
    public TestUtil (MiniAppService staticMiniAppService) {
        TestUtil .staticMiniAppService= staticMiniAppService;
    }

    public static void test() {
        staticMiniAppService.getById(1);
    }
}