Spring的Resource接口为资源访问提供了统一的接口，不同的实现类实现了从不同上下文获取资源。下面是该接口的方法:

public interface Resource extends InputStreamSource {/*** Determine 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();/*** Indicate whether the contents of this resource can be read via* {@link #getInputStream()}.* <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();/*** Indicate whether this resource represents a handle with an open stream.* If {@code 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* @since 2.5*/URI getURI() throws IOException;/*** Return a File handle for this resource.* @throws java.io.FileNotFoundException if the resource cannot be resolved as* absolute file path, i.e. if the resource is not available in a file system* @throws IOException in case of general resolution/reading failures* @see #getInputStream()*/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();}

下面列举几个常用的Resource实现类。

• AbstractResource提供了Resource的默认实现；
• UrlResource封装了一个java.net.URL对象，用来访问URL可以正常访问的任意对象，比如文件；
• 可以使用ClassPathResource来获取类路径上的资源ClassPathResource可以使用线程上下文的加载器、调用者提供的加载器或指定的类中的任意一个来加载资源；
• FileSystemResource是针对java.io.File提供的Resource实现；
• ServletContextResource为了获取web根路径的ServletContext资源而提供的Resource实现；
• 在确实没有找到其他合适的Resource实现时，才使用InputSteamResource；
• 当需要从字节数组加载内容时，ByteArrayResource是一个不错的选择，使用ByteArrayResource可以不用求助于InputStreamResource；