[spring6: Resource ResourceLoader]-加载资源

Resource

Resource 接口为处理和访问不同类型资源（如文件、URL、输入流等）提供了统一的 API，支持资源的存在性检查、读取、转换等操作。

public interface Resource extends InputStreamSource {boolean exists();default boolean isReadable() {return exists();}default boolean isOpen() {return false;}default boolean isFile() {return false;}URL getURL() throws IOException;URI getURI() throws IOException;File getFile() throws IOException;default ReadableByteChannel readableChannel() throws IOException {return Channels.newChannel(getInputStream());}default byte[] getContentAsByteArray() throws IOException {return FileCopyUtils.copyToByteArray(getInputStream());}default String getContentAsString(Charset charset) throws IOException {return FileCopyUtils.copyToString(new InputStreamReader(getInputStream(), charset));}long contentLength() throws IOException;long lastModified() throws IOException;Resource createRelative(String relativePath) throws IOException;@NullableString getFilename();String getDescription();}

public interface InputStreamSource {InputStream getInputStream() throws IOException;
}

实现类	描述
UrlResource	用于封装 java.net.URL，可以访问任何通过 URL 访问的资源，如文件、HTTPS、FTP 等。
ClassPathResource	用于从类路径加载资源，支持使用类加载器或特定类来加载资源。
FileSystemResource	基于 java.io.File 的实现，支持文件系统路径，采用 Java NIO API 进行操作。
PathResource	基于 java.nio.file.Path 的实现，采用 NIO API，支持文件和 URL 解析，且实现了 WritableResource 接口。
ServletContextResource	用于 ServletContext 资源，解析相对路径并在 Web 应用的根目录下查找资源。
InputStreamResource	封装已打开的 InputStream，适用于流式访问已打开的资源，避免多次读取。
ByteArrayResource	基于给定字节数组的实现，通过 ByteArrayInputStream 来加载内容，适合加载内存中的数据。

ResourceLoader

ResourceLoader 接口用于资源加载策略，通常在 Spring 应用中用于加载文件、类路径或其他类型的资源。它的子接口和实现类则为其功能扩展，支持不同类型的应用上下文或资源解析需求。|

public interface ResourceLoader {/** Pseudo URL prefix for loading from the class path: "classpath:". */String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;Resource getResource(String location);@NullableClassLoader getClassLoader();}

DefaultResourceLoader

DefaultResourceLoader 是 Spring 中用于加载各种类型资源的默认实现，支持通过类路径、文件系统、URL 等方式加载，并允许扩展协议解析器。

// Direct Known Subclasses:
// AbstractApplicationContext, ClassRelativeResourceLoader, FileSystemResourceLoader, ServletContextResourceLoader
public class DefaultResourceLoader implements ResourceLoader {@Nullableprivate ClassLoader classLoader;private final Set<ProtocolResolver> protocolResolvers = new LinkedHashSet<>(4);private final Map<Class<?>, Map<Resource, ?>> resourceCaches = new ConcurrentHashMap<>(4);public DefaultResourceLoader() {}public DefaultResourceLoader(@Nullable ClassLoader classLoader) {this.classLoader = classLoader;}public void addProtocolResolver(ProtocolResolver resolver) {Assert.notNull(resolver, "ProtocolResolver must not be null");this.protocolResolvers.add(resolver);}@SuppressWarnings("unchecked")public <T> Map<Resource, T> getResourceCache(Class<T> valueType) {return (Map<Resource, T>) this.resourceCaches.computeIfAbsent(valueType, key -> new ConcurrentHashMap<>());}public void clearResourceCaches() {this.resourceCaches.clear();}@Overridepublic Resource getResource(String location) {Assert.notNull(location, "Location must not be null");for (ProtocolResolver protocolResolver : getProtocolResolvers()) {Resource resource = protocolResolver.resolve(location, this);if (resource != null) {return resource;}}if (location.startsWith("/")) {return getResourceByPath(location);}else if (location.startsWith(CLASSPATH_URL_PREFIX)) {return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());}else {try {// Try to parse the location as a URL...URL url = ResourceUtils.toURL(location);return (ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url));}catch (MalformedURLException ex) {// No URL -> resolve as resource path.return getResourceByPath(location);}}}protected Resource getResourceByPath(String path) {return new ClassPathContextResource(path, getClassLoader());}protected static class ClassPathContextResource extends ClassPathResource implements ContextResource {public ClassPathContextResource(String path, @Nullable ClassLoader classLoader) {super(path, classLoader);}@Overridepublic String getPathWithinContext() {return getPath();}@Overridepublic Resource createRelative(String relativePath) {String pathToUse = StringUtils.applyRelativePath(getPath(), relativePath);return new ClassPathContextResource(pathToUse, getClassLoader());}}
}

ResourcePatternResolver

ResourcePatternResolver 是 ResourceLoader 的扩展接口，提供了通过模式（如 Ant 风格路径）解析位置并返回 Resource 对象的功能。它支持 classpath*: 前缀来获取类路径和模块路径中所有匹配的资源。

// "classpath:META-INF/config.xml" 只匹配 第一个 META-INF/config.xml
// "classpath*:META-INF/config.xml" 匹配 所有 JAR 包 和 所有 META-INF 目录 下的 config.xml// PathMatchingResourcePatternResolver
public interface ResourcePatternResolver extends ResourceLoader {String CLASSPATH_ALL_URL_PREFIX = "classpath*:";Resource[] getResources(String locationPattern) throws IOException;}

ResourceLoaderAware

ResourceLoaderAware 接口允许对象在 Spring 容器中获取并使用 ResourceLoader 来加载资源。

public interface ResourceLoaderAware {void setResourceLoader(ResourceLoader resourceLoader);
}

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