Android AsyncTask，處理不可用的服務器

Question

我正在使用本教程： http : //hmkcode.com/android-parsing-json-data/從虛擬機上的服務器獲取JSON數據。 服務器打開時，它工作正常，但服務器不可用時，我的應用程序崩潰。 我應該如何處理這種情況？

按下按鈕后，我執行：

httpAsyncTask.execute("http://localhost:3000"); //changed on purpose, it works with given IP

httpAsyncTask類：

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) {
        Toast.makeText(getBaseContext(), "Worked fine", Toast.LENGTH_LONG).show();
        goToMyActivity();
    }
}

在調試中，我的應用程序停止在：

HttpResponse httpResponse = httpclient.execute(new HttpGet(url));

int GET方法：

public static 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.e("Http:",e.toString());
        }
    return result;
}

捕獲的異常為空。

Answer 1

使用getResponseCode(); HttpURLConnection類以確保成功建立連接。

getResponseCode(); 如果連接成功，將返回200 。

                int responseCode = -1;
                feedURL = "your URL"
                HttpURLConnection connection;
                connection = (HttpURLConnection) feedURL.openConnection();
                connection.connect();
                responseCode = connection.getResponseCode();

然后使用if塊檢查connection.getResponseCode()是否返回200 。 可以使用常量HttpURLConnection.HTTP_OK代替硬編碼200 。

                if (responseCode == HttpURLConnection.HTTP_OK) {
                      // do your stuff here
                }
                else { 
                     // Show some error dialog or Toast message
                }

Answer 2

使用catch塊來捕獲超時異常（及其他）：

String message = "";
try {
    //HTTP stuff here
    if (responseCode == HttpURLConnection.HTTP_OK) {
        // do your stuff here
    } else { 
        // Show some error dialog or Toast message
    }
} catch (Exception e) {
    message  = e.getLocalizedMessage();
    e.printStackTrace();
}
// Toast message

Answer 3

如果超時，此函數將返回null，否則將發送響應

公共靜態字符串Get（字符串url）{

  // Create a new HttpClient HttpParams params = new BasicHttpParams(); // set your timeouts here HttpConnectionParams.setConnectionTimeout(params, 5000); HttpConnectionParams.setSoTimeout(params, 10000); HttpClient httpclient = new DefaultHttpClient(params); try { // Execute HTTP GET Request HttpResponse response = httpclient.execute(new HttpGet(url)); return EntityUtils.toString(response.getEntity()); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } return null; 

}