在Spring Boot中从类路径加载文件的示例

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."); 
   } 
  } 
 } 
}

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