创建Spring Boot Web应用程序时，有时有时需要从类路径中加载文件，本篇介绍在Java语言的学习中，如何在Spring Boot中从类路径加载文件，希望对相关语言的学习有所帮助。

创建Spring Boot Web应用程序时，有时有时需要从类路径中加载文件；war和jar的加载文件格式是不一样的

在下面，您将找到在WAR和JAR中加载文件的解决方案。

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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