Resource

Resource 接口為處理和訪問不同類型資源（如文件、URL、輸入流等）提供了統一的 API，支持資源的存在性檢查、讀取、轉換等操作。

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;
}

實現類	描述
UrlResource	用于封裝 java.net.URL，可以訪問任何通過 URL 訪問的資源，如文件、HTTPS、FTP 等。
ClassPathResource	用于從類路徑加載資源，支持使用類加載器或特定類來加載資源。
FileSystemResource	基于 java.io.File 的實現，支持文件系統路徑，采用 Java NIO API 進行操作。
PathResource	基于 java.nio.file.Path 的實現，采用 NIO API，支持文件和 URL 解析，且實現了 WritableResource 接口。
ServletContextResource	用于 ServletContext 資源，解析相對路徑并在 Web 應用的根目錄下查找資源。
InputStreamResource	封裝已打開的 InputStream，適用于流式訪問已打開的資源，避免多次讀取。
ByteArrayResource	基于給定字節數組的實現，通過 ByteArrayInputStream 來加載內容，適合加載內存中的數據。

ResourceLoader

ResourceLoader 接口用于資源加載策略，通常在 Spring 應用中用于加載文件、類路徑或其他類型的資源。它的子接口和實現類則為其功能擴展，支持不同類型的應用上下文或資源解析需求。|

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 中用于加載各種類型資源的默認實現，支持通過類路徑、文件系統、URL 等方式加載，并允許擴展協議解析器。

// 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 的擴展接口，提供了通過模式（如 Ant 風格路徑）解析位置并返回 Resource 對象的功能。它支持 classpath*: 前綴來獲取類路徑和模塊路徑中所有匹配的資源。

// "classpath:META-INF/config.xml" 只匹配 第一個 META-INF/config.xml
// "classpath*:META-INF/config.xml" 匹配 所有 JAR 包 和 所有 META-INF 目錄 下的 config.xml// PathMatchingResourcePatternResolver
public interface ResourcePatternResolver extends ResourceLoader {String CLASSPATH_ALL_URL_PREFIX = "classpath*:";Resource[] getResources(String locationPattern) throws IOException;}

ResourceEditor

ResourceEditor 通過繼承 PropertyEditorSupport 提供了對資源路徑的自動解析和加載功能。它能夠將字符串路徑轉換為 Resource 類型，同時支持占位符解析和動態路徑處理。這使得資源的配置和加載變得更加靈活與便捷，尤其適用于需要根據配置或環境動態加載資源的場景。

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;}}}