【译】Spring Boot 从 classpath 加载文件

介绍

在创建Spring Boot web应用程序时，有时需要从 classpath 加载文件，例如，数据仅作为文件可用的时候。在我的例子中，我使用 MAXMIND GeoLite2 数据库进行地理位置检索。因此，我需要加载文件并创建一个 DatabaseReader 对象，该对象存储在服务器内存中。
下面您将找到在WAR和JAR中加载文件的解决方案。

The ResourceLoader

Java本身提供了线程 classLoader 可以用来尝试加载文件，但 Spring 框架提供了更加优雅的方式，比如 ： ResourceLoader。

你只需要在需要的地方注入 ResourceLoader ，然后调用 getResource(“some path”) 方法即可。

从 resource 目录或 classpath 中加载文件 的例子 (WAR)

@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.");
            }
        }
    }
}

从 Spring Boot JAR 中加载文件的例子

@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.");
            }
        }
    }
}

英文原文：https://smarterco.de/java-load-file-from-classpath-in-spring-boot/?from=timeline