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.");
  }
 }
}
}

来源：https://developer.51cto.com/art/202009/627661.htm