在Spring Boot中从类路径加载文件

缺乏、安全感 2022-12-06 12:59 127阅读 0赞

## 介绍 ##

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.");
                }
            }
        }
    }

[Spring Boot]: http://projects.spring.io/spring-boot/
[ResourceLoader]: http://docs.spring.io/spring/docs/current/spring-framework-reference/html/resources.html