Android Jamendo源码分析之 网络连接模块

程序中实现网络连接和获取网络数据是通过JamendoGet2Api这个接口中的方法实现的，他的实现类是JamendoGet2ApiImpl.这里就以getPopularAlbumsWeek()这个函数为例分析.

class JamendoGet2ApiImpl中

getPopularAlbumsWeek函数源码:

@Override
public Album[] getPopularAlbumsWeek() throws JSONException, WSError {

String jsonString = doGet("id+name+url+image+rating+artist_name/album/json/?n=20&order=ratingweek_desc");
if(jsonString == null)
return null;
JSONArray jsonArrayAlbums = new JSONArray(jsonString);
return AlbumFunctions.getAlbums(jsonArrayAlbums);

}
首先通过doGet方法根据指定的url通过HTTP协议获取网络数据。
里面的 doGet函数 调用 Caller.doGet
函数返回网络数据。

Caller.get 函数源码：

public static String doGet(String url) throws WSError{

String data = null;
if(requestCache != null){
data = requestCache.get(url);
if(data != null){
Log.d(JamendoApplication.TAG, "Caller.doGet [cached] "+url);
return data;
}
}

// initialize HTTP GET request objects
HttpClient httpClient = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(url);
HttpResponse httpResponse;

try {
// execute request
try {
httpResponse = httpClient.execute(httpGet);
} catch (UnknownHostException e) {
WSError wsError = new WSError();
wsError.setMessage(e.getLocalizedMessage());
throw wsError;
} catch (SocketException e){
WSError wsError = new WSError();
wsError.setMessage(e.getLocalizedMessage());
throw wsError;
}

// request data
HttpEntity httpEntity = httpResponse.getEntity();

if(httpEntity != null){
InputStream inputStream = httpEntity.getContent();
data = convertStreamToString(inputStream);
// cache the result
if(requestCache != null){
requestCache.put(url, data);
}
}

} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}

Log.d(JamendoApplication.TAG, "Caller.doGet "+url);
return data;
}
根据返回的字符串数据创建JSONArray对象:
JSONArray jsonArrayAlbums = new JSONArray(jsonString);
然后根据AlbumFunctions的静态函数getAlbums将封装在JSONArray中字符串数据转换为Album对象，然后放在数组中返回:

return AlbumFunctions.getAlbums(jsonArrayAlbums);

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其中的 RequestCache类，类似一缓冲区

将访问数据，暂存于HashTable中，到需要访问一个url获取网络数据是，先到缓冲区中去查找，若查找到则直接返回，否则联网获取。