6.请求网络步骤

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();
}