[spring6: Resource ResourceLoader ResourceEditor]-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;
}

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;}

ResourceEditor

ResourceEditor 通过继承 PropertyEditorSupport 提供了对资源路径的自动解析和加载功能。它能够将字符串路径转换为 Resource 类型，同时支持占位符解析和动态路径处理。这使得资源的配置和加载变得更加灵活与便捷，尤其适用于需要根据配置或环境动态加载资源的场景。

public class ResourceEditor extends PropertyEditorSupport {private final ResourceLoader resourceLoader;@Nullableprivate PropertyResolver propertyResolver;private final boolean ignoreUnresolvablePlaceholders;public ResourceEditor() {this(new DefaultResourceLoader(), null);}public ResourceEditor(ResourceLoader resourceLoader, @Nullable PropertyResolver propertyResolver) {this(resourceLoader, propertyResolver, true);}public ResourceEditor(ResourceLoader resourceLoader, @Nullable PropertyResolver propertyResolver,boolean ignoreUnresolvablePlaceholders) {Assert.notNull(resourceLoader, "ResourceLoader must not be null");this.resourceLoader = resourceLoader;this.propertyResolver = propertyResolver;this.ignoreUnresolvablePlaceholders = ignoreUnresolvablePlaceholders;}@Overridepublic void setAsText(String text) {if (StringUtils.hasText(text)) {String locationToUse = resolvePath(text).trim();setValue(this.resourceLoader.getResource(locationToUse));}else {setValue(null);}}protected String resolvePath(String path) {if (this.propertyResolver == null) {this.propertyResolver = new StandardEnvironment();}return (this.ignoreUnresolvablePlaceholders ? this.propertyResolver.resolvePlaceholders(path) :this.propertyResolver.resolveRequiredPlaceholders(path));}@Override@Nullablepublic String getAsText() {Resource value = (Resource) getValue();try {return (value != null ? value.getURL().toExternalForm() : "");}catch (IOException ex) {return null;}}}