Spring 配置資源Resource，spring資源resource

Spring 配置資源Resource，spring資源resource
Java中，不同來源的資源抽象成URL，通過註冊不同的handler（URLStreamHandler)來處理不同來源的資源的讀取邏輯。一般handler的類型使用不同的首碼（協議，protocal）來識別，如：“file：”、“http：“、”jar：”等。 對於Spring，URL沒有定義相應的，如“classpath：“的handler，定義也相對麻煩，Spring對設定檔的讀取做了相應的封裝，通過Resource介面來抽象底層資源。如下：

/** * Interface for a resource descriptor that abstracts from the actual * type of underlying resource, such as a file or class path resource. * * <p>An InputStream can be opened for every resource if it exists in * physical form, but a URL or File handle can just be returned for * certain resources. The actual behavior is implementation-specific. * * @author Juergen Hoeller * @since 28.12.2003 * @see #getInputStream() * @see #getURL() * @see #getURI() * @see #getFile() * @see WritableResource * @see ContextResource * @see FileSystemResource * @see ClassPathResource * @see UrlResource * @see ByteArrayResource * @see InputStreamResource * @see PathResource */public interface Resource extends InputStreamSource {    /**     * Return whether this resource actually exists in physical form.     * <p>This method performs a definitive existence check, whereas the     * existence of a {@code Resource} handle only guarantees a     * valid descriptor handle.     */    boolean exists();    /**     * Return whether the contents of this resource can be read,     * e.g. via {@link #getInputStream()} or {@link #getFile()}.     * <p>Will be {@code true} for typical resource descriptors;     * note that actual content reading may still fail when attempted.     * However, a value of {@code false} is a definitive indication     * that the resource content cannot be read.     * @see #getInputStream()     */    boolean isReadable();    /**     * Return whether this resource represents a handle with an open     * stream. If true, the InputStream cannot be read multiple times,     * and must be read and closed to avoid resource leaks.     * <p>Will be {@code false} for typical resource descriptors.     */    boolean isOpen();    /**     * Return a URL handle for this resource.     * @throws IOException if the resource cannot be resolved as URL,     * i.e. if the resource is not available as descriptor     */    URL getURL() throws IOException;    /**     * Return a URI handle for this resource.     * @throws IOException if the resource cannot be resolved as URI,     * i.e. if the resource is not available as descriptor     */    URI getURI() throws IOException;    /**     * Return a File handle for this resource.     * @throws IOException if the resource cannot be resolved as absolute     * file path, i.e. if the resource is not available in a file system     */    File getFile() throws IOException;    /**     * Determine the content length for this resource.     * @throws IOException if the resource cannot be resolved     * (in the file system or as some other known physical resource type)     */    long contentLength() throws IOException;    /**     * Determine the last-modified timestamp for this resource.     * @throws IOException if the resource cannot be resolved     * (in the file system or as some other known physical resource type)     */    long lastModified() throws IOException;    /**     * Create a resource relative to this resource.     * @param relativePath the relative path (relative to this resource)     * @return the resource handle for the relative resource     * @throws IOException if the relative resource cannot be determined     */    Resource createRelative(String relativePath) throws IOException;    /**     * Determine a filename for this resource, i.e. typically the last     * part of the path: for example, "myfile.txt".     * <p>Returns {@code null} if this type of resource does not     * have a filename.     */    String getFilename();    /**     * Return a description for this resource,     * to be used for error output when working with the resource.     * <p>Implementations are also encouraged to return this value     * from their {@code toString} method.     * @see Object#toString()     */    String getDescription();}

對於不同來源的資源檔都有相應的Resource實現，檔案（FileSystemResource）、Classpath資源（ClassPathResource）、URL資源（UrlResource）、InputStream資源（InputStreamResource）、Byte數組資源（ByteArrayResource）等。