Android中從URL取得JSON格式

首先要先搞清楚其JSON Structure 並了解其JSONObject與JSONArray所盼演的角色，看底下圖。

想要在Android當中從URL取得JSON格式，大概需要執行以下步驟：

      1. 增加網路權限，在AndroidManifest.xml當中加入以下：

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

      2. 使用HttpClient與HttpResponse方法Parse URL並取得JSON String。

      3. 建立JSONObject與JSONArray來處理JSON String。

      4. 從JSONObject與JSONArray取出你要的資料。

請記得一定要使用AsyncTask來處理，因為這是UI Thread。


以下為具體程式碼:

其中我們要取得的JSON格式來源：http://hmkcode.appspot.com/rest/controller/get.json

{"articleList":
    [{
        "title":"Android Internet Connection Using HTTP GET (HttpClient)",
        "url":"http://hmkcode.com/android-internet-connection-using-http-get-httpclient/",
        "categories":["Android"],
        "tags":["android","httpclient","internet"]
    },
    {
        "title":" Android | Taking Photos with Android Camera ",
        "url":"http://hmkcode.com/android-camera-taking-photos-camera/",
        "categories":["Android"],
        "tags":["android","camera"]
    }]
}

java程式中的AsyncTask核心部份：

private class HttpAsyncTask extends AsyncTask<String, Void, String> {
    @Override
    protected String doInBackground(String... urls) {
        return GET(urls[0]);
    }
    // onPostExecute displays the results of the AsyncTask.
    @Override
    protected void onPostExecute(String result) {
        try {
            JSONObject json = new JSONObject(result);

            String str = "";

            JSONArray articles = json.getJSONArray("articleList");
            str += "articles length = "+json.getJSONArray("articleList").length();
            str += "\n--------\n";
            str += "names: "+articles.getJSONObject(0).names();
            str += "\n--------\n";
            str += "url: "+articles.getJSONObject(0).getString("url");

        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    private  String GET(String url){
        InputStream inputStream = null;
        String result = "";
        try {

            // create HttpClient
            HttpClient httpclient = new DefaultHttpClient();

            // make GET request to the given URL
            HttpResponse httpResponse = httpclient.execute(new HttpGet(url));

            // receive response as inputStream
            inputStream = httpResponse.getEntity().getContent();

            // convert inputstream to string
            if(inputStream != null)
                result = convertInputStreamToString(inputStream);
            else
                result = "Did not work!";

        } catch (Exception e) {
            Log.d("InputStream", e.getLocalizedMessage());
        }

        return result;
    }

    private  String convertInputStreamToString(InputStream inputStream) throws IOException {
        BufferedReader bufferedReader = new BufferedReader( new InputStreamReader(inputStream));
        String line = "";
        String result = "";
        while((line = bufferedReader.readLine()) != null)
            result += line;

        inputStream.close();
        return result;

    }
}             

其使用方式很簡單，在你的主程式當中加入以下調用：

new HttpAsyncTask().execute("http://hmkcode.appspot.com/rest/controller/get.json");

上述當中以及實現了從URL中取得JSON格式，並放至str中，我這裡是沒有將他印出，而你當然可以使用Log印出看看str，或者是你想顯示在圖形界面，隨便你。



Reference:

• http://hmkcode.com/android-parsing-json-data/
• http://www.androidhive.info/2012/01/android-json-parsing-tutorial/