在Spring Boot中从类路径加载文件解决方案

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."); 
            } 
        } 
    } 
} 

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."); 
            } 
        } 
    } 
}