资源加载器

使用Java，您可以使用当前线程的classLoader并尝试加载文件，但是Spring Framework为您提供了更为优雅的解决方案，例如ResourceLoader。

您只需要自动连接ResourceLoader，然后调用getResource(„somePath“)方法即可。

在Spring Boot（WAR）中从资源目录/类路径加载文件的示例

在以下示例中，我们从类路径中加载名为GeoLite2-Country.mmdb的文件作为资源，然后将其作为File对象检索。

@Service("geolocationservice") 
public class GeoLocationServiceImpl implements GeoLocationService { 
  private static final Logger LOGGER = LoggerFactory.getLogger(GeoLocationServiceImpl.class); 
  private static DatabaseReader reader = null; 
  private ResourceLoader resourceLoader; 
  @Autowired 
  public GeoLocationServiceImpl(ResourceLoader resourceLoader) { 
    this.resourceLoader = resourceLoader; 
  }  @PostConstruct 
  public void init() { 
    try { 
      LOGGER.info("GeoLocationServiceImpl: Trying to load GeoLite2-Country database..."); 
      Resource resource = resourceLoader.getResource("classpath:GeoLite2-Country.mmdb"); 
      File dbAsFile = resource.getFile();      // Initialize the reader 
      reader = new DatabaseReader 
            .Builder(dbAsFile) 
            .fileMode(Reader.FileMode.MEMORY) 
            .build(); 
      LOGGER.info("GeoLocationServiceImpl: Database was loaded successfully."); 
    } catch (IOException | NullPointerException e) { 
      LOGGER.error("Database reader cound not be initialized. ", e); 
    } 
  } 
  @PreDestroy 
  public void preDestroy() { 
    if (reader != null) { 
      try { 
        reader.close(); 
      } catch (IOException e) { 
        LOGGER.error("Failed to close the reader."); 
      } 
    } 
  } 
} 

在Spring Boot（JAR）中从资源目录/类路径加载文件的示例

如果您想从Spring Boot JAR中的 classpath加载文件，则必须使用该resource.getInputStream()方法将其作为InputStream检索。如果尝试使用resource.getFile()该方法，则会收到错误消息，因为Spring尝试访问文件系统路径，但无法访问JAR中的路径。

@Service("geolocationservice") 
public class GeoLocationServiceImpl implements GeoLocationService { 
  private static final Logger LOGGER = LoggerFactory.getLogger(GeoLocationServiceImpl.class); 
  private static DatabaseReader reader = null; 
  private ResourceLoader resourceLoader; 
  @Inject 
  public GeoLocationServiceImpl(ResourceLoader resourceLoader) { 
    this.resourceLoader = resourceLoader; 
  }  @PostConstruct 
  public void init() { 
    try { 
      LOGGER.info("GeoLocationServiceImpl: Trying to load GeoLite2-Country database..."); 
      Resource resource = resourceLoader.getResource("classpath:GeoLite2-Country.mmdb"); 
      InputStream dbAsStream = resource.getInputStream(); // <-- this is the difference 
      // Initialize the reader 
      reader = new DatabaseReader 
            .Builder(dbAsStream) 
            .fileMode(Reader.FileMode.MEMORY) 
            .build(); 
      LOGGER.info("GeoLocationServiceImpl: Database was loaded successfully."); 
    } catch (IOException | NullPointerException e) { 
      LOGGER.error("Database reader cound not be initialized. ", e); 
    } 
  } 
  @PreDestroy 
  public void preDestroy() { 
    if (reader != null) { 
      try { 
        reader.close(); 
      } catch (IOException e) { 
        LOGGER.error("Failed to close the reader."); 
      } 
    } 
  } 
}