Android開發18——獲取網絡資源之json數據

本文出自 “IT徐胖子的專欄” 博客，請務必保留此出處http://woshixy.blog.51cto.com/5637578/1088074

一、項目背景
在Android開發中有一項非常廣泛的應用：Android項目獲取另一個web項目的資源或者返回的數據。
本文獲取web項目返回的JSON數據。Android應用解析JSON比XML性能要好，但有許多項目仍然採用的是XML。

二、實例代碼

Web項目

/**
 * 新聞業務類
 *
 * @author 徐越
 *
 */
publicclass VideoNewsServiceImpl implements VideoNewsService
{
public List<VideoNews> readNews()
    {
        List<VideoNews> lst = new ArrayList<VideoNews>();
        lst.add(new VideoNews(1, "喜洋洋", 20));
        lst.add(new VideoNews(2, "變形金剛", 10));
        lst.add(new VideoNews(3, "功夫熊貓", 20));
return lst;
    }
}

/**
 * 新聞Servlet
 *
 * @author 徐越
 *
 */
publicclass ListServlet extends HttpServlet
{
privatestaticfinallong serialVersionUID = 1L;
private VideoNewsService vs = new VideoNewsServiceImpl();

protectedvoid doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
    {
        doPost(request, response);
    }

protectedvoid doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
    {
        List<VideoNews> news = vs.readNews();
        JSONArray jsonarr = JSONArray.fromObject(news);
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/plain;charset=UTF-8");
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);
        response.getWriter().print(jsonarr);
    }
}

Android項目

publicclass VideoNewsServiceImpl implements VideoNewsService
{

/**
     * 獲取最新視頻資訊，從JSON文件中，解析效率高
     *
     * @return
     * @throws Exception
     */
public List<VideoNews> getNewsFromJson() throws Exception
    {
        List<VideoNews> lst = new ArrayList<VideoNews>();
        String path = "http://xxx.xxx.xxx.xxx:8080/web/ListServlet";
        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setReadTimeout(5000);
        conn.setRequestMethod("GET");
if (200 == conn.getResponseCode())
        {
            InputStream instream = conn.getInputStream();
            lst = parseJSON(instream);
        }
return lst;
    }

/**
     * 解析JSON
     */
private List<VideoNews> parseJSON(InputStream instream) throws Exception
    {
        List<VideoNews> lst = new ArrayList<VideoNews>();
byte[] data = IOUtils.read(instream);
        String jsonStr = new String(data);
        JSONArray array = new JSONArray(jsonStr);
for (int i = 0; i < array.length(); i++)
        {
            JSONObject jsonObj = (JSONObject) array.getJSONObject(i);
            VideoNews v = new VideoNews(jsonObj.getInt("id"),
                    jsonObj.getString("title"), jsonObj.getInt("timeLength"));
            lst.add(v);
        }
return lst;
    }
}

/**
 * IO操作工具類
 *
 * @author 徐越
 *
 */
publicclass IOUtils
{
/**
     * 讀取輸入流爲byte[]數組
     */
publicstaticbyte[] read(InputStream instream) throws IOException
    {
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
byte[] buffer = newbyte[1024];
int len = 0;
while ((len = instream.read(buffer)) != -1)
        {
            bos.write(buffer, 0, len);
        }
return bos.toByteArray();
    }
}

需要指出的是
在web項目中我採用的是net.sf.json下的類對JSON進行解析，而Android項目中默認自帶的JSON包是org.json。API有所不同，只要熟悉一下即可。

本文出自 “IT徐胖子的專欄” 博客，請務必保留此出處http://woshixy.blog.51cto.com/5637578/1088074