Spring3.2 资源(Resource)管理

可以看到Resource继承自InputStreamSource，该接口定义了getInputStream()方法，用于获取资源对应的输入流对象。Spring中也提供了多种Resource实现，这可以从Resource继承树中看出:

其中有我们比较熟悉的ClasspathResource(类路径资源，Main应用程序常用)，FileSystemResource(文件系统资源)等，所有Resource的实现均继承自AbstractResource，其实现了一些基本功能:

public abstract class AbstractResource implements Resource {	public boolean exists() {		try {			// 先从文件系统查看文件是否存在			return getFile().exists();		} catch (IOException ex) {			// Fall back to stream existence: can we open the stream?			try {				InputStream is = getInputStream();				is.close();				return true;			}			catch (Throwable isEx) {				return false;			}		}	}	public boolean isReadable() {		return true;	}	public boolean isOpen() {		return false;	}	/**	 * 需由具体子类实现	 */	public URL getURL() throws IOException {		throw new FileNotFoundException(getDescription() + " cannot be resolved to URL");	}	public URI getURI() throws IOException {		URL url = getURL();		try {			// URL -> URI			return ResourceUtils.toURI(url);		} catch (URISyntaxException ex) {			throw new NestedIOException("Invalid URI [" + url + "]", ex);		}	}	/**	 * 需由具体子类实现	 */	public File getFile() throws IOException {		throw new FileNotFoundException(getDescription() + " cannot be resolved to absolute file path");	}	/**	 * 通过输入流对象读取资源内容长度	 */	public long contentLength() throws IOException {		InputStream is = this.getInputStream();		Assert.state(is != null, "resource input stream must not be null");		try {			long size = 0;			byte[] buf = new byte[255];			int read;			while ((read = is.read(buf)) != -1) {				size += read;			}			return size;		} finally {			try {				is.close();			} catch (IOException ex) {			}