6.请求网络步骤

public class FileUtils {	public static final String CACHE = "cache";	public static final String ICON = "icon";	public static final String ROOT = "GooglePlay";	/**	 * 获取图片的缓存的路径	 * 	 * @return	 */	public static File getIconDir() {		return getDir(ICON);	}	/**	 * 获取缓存路径	 * 	 * @return	 */	public static File getCacheDir() {		return getDir(CACHE);	}	public static File getDir(String cache) {		StringBuilder path = new StringBuilder();		if (isSDAvailable()) {			path.append(Environment.getExternalStorageDirectory()					.getAbsolutePath());			path.append(File.separator);// '/'			path.append(ROOT);// /mnt/sdcard/GooglePlay			path.append(File.separator);			path.append(cache);// /mnt/sdcard/GooglePlay/cache		} else {			File filesDir = UiUtils.getContext().getCacheDir(); // cache																// getFileDir																// file			path.append(filesDir.getAbsolutePath());// /data/data/com.itheima.googleplay/cache			path.append(File.separator);// /data/data/com.itheima.googleplay/cache/			path.append(cache);// /data/data/com.itheima.googleplay/cache/cache		}		File file = new File(path.toString());		if (!file.exists() || !file.isDirectory()) {			file.mkdirs();// 创建文件夹		}		return file;	}	private static boolean isSDAvailable() {		if (Environment.getExternalStorageState().equals(				Environment.MEDIA_MOUNTED)) {			return true;		} else {			return false;		}	}}

public abstract class BaseProtocol<T> {	public T load(int index) {		// 加载本地数据		String json = loadLocal(index);		if (json == null) {			// 请求服务器			json = loadServer(index);			if (json != null) {				saveLocal(json, index);			}		}		if (json != null) {			return paserJson(json);		} else {			return null;		}	}	private String loadServer(int index) {		HttpResult httpResult = HttpHelper.get(HttpHelper.URL +getKey()//请求网络，写xutils也行				+ "?index=" + index); 		String json = httpResult.getString();		return json;	}	private void saveLocal(String json, int index) {				BufferedWriter bw = null;		try {			File dir=FileUtils.getCacheDir();			//在第一行写一个过期时间 			File file = new File(dir, getKey()+"_" + index); // /mnt/sdcard/googlePlay/cache/home_0			FileWriter fw = new FileWriter(file);			 bw = new BufferedWriter(fw);			bw.write(System.currentTimeMillis() + 1000 * 100 + "");//如果数字过期了重新请求网络			bw.newLine();// 换行			bw.write(json);// 把整个json文件保存起来			bw.flush();			bw.close();		} catch (Exception e) {			e.printStackTrace();		}finally{			IOUtils.closeQuietly(bw);//关流		}	}	private String loadLocal(int index) {		//  如果发现文件已经过期了 就不要再去复用缓存了		File dir=FileUtils.getCacheDir();// 获取缓存所在的文件夹		File file = new File(dir, getKey()+"_" + index); 		try {			FileReader fr=new FileReader(file);			BufferedReader br=new BufferedReader(fr);			long outOfDate = Long.parseLong(br.readLine());			if(System.currentTimeMillis()>outOfDate){				return null;			}else{				String str=null;				String sw=new StringWriter();				while((str=br.readLine())!=null){									sw.write(str);				}				return sw.toString();			}					} catch (Exception e) {			e.printStackTrace();			return null;		}	}	/**	 * 解析json	 * @param json	 * @return	 */	public abstract T paserJson(String json);	/**	 * 说明了关键字	 * @return	 */	public abstract String getKey();}