存储库未启动

Question

尝试将存储库启动从我的应用程序类移动到配置类时出现错误。这似乎很奇怪，因为 urlRepository.save 调用没有抛出，而 urlRepository.findAll() 得到一个空值。我在这里做错了什么？

之前（工作正常 - 使用预加载的 URL 打印到控制台）

@SpringBootApplication
public class UrlShortenerApplication implements CommandLineRunner {

@Autowired
private UrlRepository urlRepository = new MongoUrlRepository();

public static void main(String[] args) {
    SpringApplication.run(UrlShortenerApplication.class, args);
}

@Override
public void run(String... args) throws Exception {

    String shortlinkStub = "short.li/";
    String cascadeDishPods = "https://www.amazon.com/gp/product/B07CTQ8THP/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1";
    String flipFlops = "https://www.amazon.com/gp/product/B0013MWDO0/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1";
    urlRepository.save(new ShortUrl(shortlinkStub + "flipflops", flipFlops));
    urlRepository.findAll().forEach(shortUrl -> System.out.println("Preloaded " + shortUrl));
}
}

之后（repository.findAll() 的空指针异常）

ShortenerConfig.java

@Configuration
public class ShortenerConfig {

public static UrlRepository urlRepository = new MongoUrlRepository();

@Bean("urlRepo")
public UrlRepository urlRepo() {
    return urlRepository;
}
}

UrlShortenerApplication.java

@SpringBootApplication
public class UrlShortenerApplication implements CommandLineRunner {

    @Autowired
    @Qualifier("urlRepo")
    private UrlRepository urlRepository;

    public static void main(String[] args) {

        SpringApplication.run(UrlShortenerApplication.class, args);
    }

    @Override
    public void run(String... args) throws Exception {

        String shortlinkStub = "short.li/";
        String cascadeDishPods = "https://www.amazon.com/gp/product/B07CTQ8THP/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1";
        String flipFlops = "https://www.amazon.com/gp/product/B0013MWDO0/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1";
        urlRepository.save(new ShortUrl(shortlinkStub + "flipflops", flipFlops));
        urlRepository.findAll().forEach(shortUrl -> System.out.println("Preloaded " + shortUrl));
    }
}

最后一行抛出空指针异常，我不知道为什么！

堆栈跟踪

第 22 行是指“运行”，第 35 行是指 reponsitory.findAll()

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2020-06-12 10:48:25.813 ERROR 75530 --- [           main] o.s.boot.SpringApplication               : Application run failed

java.lang.IllegalStateException: Failed to execute CommandLineRunner
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:798) ~[spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:779) ~[spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:322) ~[spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1237) ~[spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) ~[spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    at com.example.urlshortener.UrlShortenerApplication.main(UrlShortenerApplication.java:22) ~[main/:na]
Caused by: java.lang.NullPointerException: null
    at com.example.urlshortener.UrlShortenerApplication.run(UrlShortenerApplication.java:35) ~[main/:na]
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:795) ~[spring-boot-2.3.0.RELEASE.jar:2.3.0.RELEASE]
    ... 5 common frames omitted

2020-06-12 10:48:25.843  INFO 75530 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Shutting down ExecutorService 'applicationTaskExecutor'

存储库接口和类（适用于两种情况）

public interface UrlRepository extends MongoRepository<ShortUrl, Long> {
    public ShortUrl findByShortUrl(String shortUrl); 
    public List<ShortUrl> findByLongUrl(String longUrl);

}

public class MongoUrlRepository implements UrlRepository {
    @Override
    public ShortUrl findByShortUrl(String shortUrl) {
        return null;
    }

    @Override
    public List<ShortUrl> findByLongUrl(String longUrl) {
        return null;
    }

....

Answer 1

MongoUrlRepository 应该是一个接口，这就是 Spring 可以自动管理它的 crud 实现的方式。由于您将其声明为一个类，因此您基本上覆盖了内置的查找器方法以仅返回 null，这就是您的 NPE 的来源。

查看 spring.io 中的示例： https://spring.io/guides/gs/accessing-data-mongodb/

为什么它在第一种情况下有效：

@Autowired
private UrlRepository urlRepository = new MongoUrlRepository();

您实例化了一个 MongoUrlRepository，但是该对象将在依赖注入期间被替换，并且由于您没有指定限定符，spring 将构建一个托管的 MongoRepository bean（基于您的 UrlRepository 接口）并忽略您的 MongoUrlRepository 类。