在Spring Boot中從類路徑加載文件

介紹

創建Spring Boot Web應用程序時，有時有時需要從類路徑中加載文件；war和jar的加載文件格式是不一樣的

在下面，您將找到在WAR和JAR中加載文件的解決方案。

資源加載器

使用Java，您可以使用當前線程的classLoader並嘗試加載文件，但是Spring Framework為您提供了更為優雅的解決方案，例如ResourceLoader。

您只需要自動連接ResourceLoader，然后調用getResource(„somePath“)方法即可。

在Spring Boot（WAR）中從資源目錄/類路徑加載文件的示例

在以下示例中，我們從類路徑中加載名為GeoLite2-Country.mmdb的文件作為資源，然后將其作為File對象檢索。

@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）中從資源目錄/類路徑加載文件的示例

 如果您想從Spring Boot JAR中的 classpath加載文件，則必須使用該resource.getInputStream()方法將其作為InputStream檢索。如果嘗試使用resource.getFile()該方法，則會收到錯誤消息，因為Spring嘗試訪問文件系統路徑，但無法訪問JAR中的路徑。

@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.");
            }
        }
    }
}