從今天開始，一步步走上源碼分析的路。剛開始肯定要從簡單著手。我們先從java發展史上最強大的框架——Spring、、、旗下的資源抽象接口Resource開始吧。

　　我看了好多分析Spring源碼的，每每一開始就是Spring IOC、AOP、BeanFactory這樣的Spring典型模塊，實在看厭了，這些暫且留到以后。我的想法是，分析就分析別人沒分析過的，或者以不同的角度來分析別人分析過的。

　　可能很多用了Spring多年的程序員對Resource都了解有限，畢竟訪問資源一般是搭建web工程框架的時候的事情。不過了解它也是非常有好處的。

　　這個接口的作用是可以讓我們更方便操縱底層資源。因為JDK操縱底層資源基本就是 java.net.URL 、java.io.File 、java.util.Properties這些。取資源基本是根據絕對路徑或當前類的相對路徑來取。從類路徑或Web容器上下文中獲取資源的時候也不方便。Resource接口提供了更強大的訪問底層資源的能力。

　　廢話不多說，看源碼之前先來看一下Resource的類結構。

一、類結構

一、Resource接口

　　如圖，Resouce接口并不是一個根接口，它繼承了一個簡單的父接口%20InputStreamSource，這個接口只有一個方法，用以返回一個輸入流：

InputStream%20getInputStream()%20throws%20IOException;

　　來，直接上Resource接口的源碼，中文是我根據英文注釋自己翻譯的，如下：

public%20interface%20Resource%20extends%20InputStreamSource%20{%20%20%20%20boolean%20exists();%20%20%20%20%20%20//%20%20資源是否存在%20%20%20%20boolean%20isReadable();%20%20//%20%20資源是否可讀%20%20%20%20boolean%20isOpen();%20%20%20%20%20%20//%20%20資源所代表的句柄是否被一個stream打開了%20%20%20%20URL%20getURL()%20throws%20IOException;%20%20%20//%20%20返回資源的URL的句柄%20%20%20%20URI%20getURI()%20throws%20IOException;%20%20%20//%20%20返回資源的URI的句柄%20%20%20%20File%20getFile()%20throws%20IOException;%20//%20%20返回資源的File的句柄%20%20%20%20long%20contentLength()%20throws%20IOException;%20%20%20//%20%20資源內容的長度%20%20%20%20long%20lastModified()%20throws%20IOException;%20%20%20%20//%20%20資源最后的修改時間%20%20%20%20Resource%20createRelative(String%20relativePath)%20throws%20IOException;%20%20%20//根據資源的相對路徑創建新資源%20%20%20%20String%20getFilename();%20%20//%20%20資源的文件名%20%20%20%20String%20getDescr
/* * Copyright 2002-2011 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package org.springframework.core.io;import java.io.File;import java.io.IOException;import java.io.InputStream;import java.net.HttpURLConnection;import java.net.URI;import java.net.URL;import java.net.URLConnection;import org.springframework.util.ResourceUtils;/** * Abstract base class for resources which resolve URLs into File references, * such as {@link UrlResource} or {@link ClassPathResource}. * * <p>Detects the "file" protocol as well as the JBoss "vfs" protocol in URLs, * resolving file system references accordingly. * * @author Juergen Hoeller * @since 3.0 */public abstract class AbstractFileResolvingResource extends AbstractResource {    @Override    public File getFile() throws IOException { //  通過資源的URL得到資源本身，是文件就返回文件，否則返回描述        URL url = getURL();        if (url.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {            return VfsResourceDelegate.getResource(url).getFile();        }        return ResourceUtils.getFile(url, getDescription());    }    @Override    protected File getFileForLastModifiedCheck() throws IOException {  //從<壓縮文件地址>中獲取文件        URL url = getURL();        if (ResourceUtils.isJarURL(url)) {            URL actualUrl = ResourceUtils.extractJarFileURL(url);            if (actualUrl.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {                return VfsResourceDelegate.getResource(actualUrl).getFile();            }            return ResourceUtils.getFile(actualUrl, "Jar URL");        }        else {            return getFile();        }    }    protected File getFile(URI uri) throws IOException {   //  通過資源uri獲取文件        if (uri.getScheme().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {            return VfsResourceDelegate.getResource(uri).getFile();        }        return ResourceUtils.getFile(uri, getDescription());    }    @Override    public boolean exists() {  //判斷資源是否存在，如果是文件Url,直接獲取文件判斷，否則，建立連接來判斷。        try {            URL url = getURL();            if (ResourceUtils.isFileURL(url)) {                // Proceed with file system resolution...                return getFile().exists();            }            else {                // Try a URL connection content-length header...                URLConnection con = url.openConnection();                ResourceUtils.useCachesIfNecessary(con);                HttpURLConnection httpCon =                        (con instanceof HttpURLConnection ? (HttpURLConnection) con : null);                if (httpCon != null) {                    httpCon.setRequestMethod("HEAD");                    int code = httpCon.getResponseCode();                    if (code == HttpURLConnection.HTTP_OK) {                        return true;                    }                    else if (code == HttpURLConnection.HTTP_NOT_FOUND) {                        return false;                    }                }                if (con.getContentLength() >= 0) {                    return true;                }                if (httpCon != null) {                    // no HTTP OK status, and no content-length header: give up                    httpCon.disconnect();                    return false;                }                else {                    // Fall back to stream existence: can we open the stream?                    InputStream is = getInputStream();                    is.close();                    return true;                }            }        }        catch (IOException ex) {            return false;        }    }    @Override    public boolean isReadable() {  //  是否可讀        try {            URL url = getURL();            if (ResourceUtils.isFileURL(url)) {                // Proceed with file system resolution...                File file = getFile();                return (file.canRead() && !file.isDirectory());            }            else {                return true;            }        }        catch (IOException ex) {            return false;        }    }    @Override    public long contentLength() throws IOException {        URL url = getURL();        if (ResourceUtils.isFileURL(url)) {            // Proceed with file system resolution...            return getFile().length();        }        else {            // Try a URL connection content-length header...            URLConnection con = url.openConnection();            ResourceUtils.useCachesIfNecessary(con);            if (con instanceof HttpURLConnection) {                ((HttpURLConnection) con).setRequestMethod("HEAD");            }            return con.getContentLength();