无法使用Android连接到数据库

我正在尝试执行以下代码，以使用Web服务从数据库中检索数据：

protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); getData(); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; } public void getData(){ TextView resultView = (TextView) findViewById(R.id.textView1); String result = ""; InputStream isr = null; try{ HttpClient httpclient = new DefaultHttpClient(); HttpPost httppost = new HttpPost("http://HOSTNAME/FILENAME.php"); HttpResponse response = httpclient.execute(httppost); HttpEntity entity = response.getEntity(); isr = entity.getContent(); } catch(Exception e){ Log.e("log_tag","Error in http connection"+e.toString()); resultView.setText("Couldnt connect to database"); } //converting to string try{ BufferedReader reader = new BufferedReader(new InputStreamReader(isr,"iso-8859-1"),8); StringBuilder sb = new StringBuilder(); String line = null; while ((line = reader.readLine()) != null){ sb.append(line + "\n"); } isr.close(); result = sb.toString(); } catch(Exception e){ Log.e("log_tag", "Error converting result"+ e.toString()); } //parse data try{ String s = ""; JSONArray jArray = new JSONArray(result); for(int i = 0;i<jArray.length();i++){ JSONObject json = jArray.getJSONObject(i); s = s + "St.ID" + json.getString("StId") + "\n " +json.getString("StName") + "\n" + json.getString("StMail"); } resultView.setText(s); } catch(Exception e){ Log.e("Log_tage", "Error Parsing Data"+e.toString()); } } 

但是错误返回：无法连接到数据库。

这是输出LogCat：

11-14 20：10：3​​5.057：E / log_tag（5323）：http connectionandroid.os.NetworkOnMainThreadException错误

11-14 20：10：3​​5.057：E / log_tag（5323）：转换resultjava.lang.NullPointerException时出错：lock == null

11-14 20：10：3​​5.057：E / Log_tage（5323）：错误解析Dataorg.json.JSONException：字符0处的输入结束

我在某些Web服务上添加了一个php文件并且它运行良好，但我认为这是关于HttpPost URL，HttpPost URL是否有特定格式，或者它是否与Web服务中给出的URL相同？

PHP文件：

请帮忙。

Answer 1

HttpPost URL没有特定的格式，它与Web服务中提供的URL相同。

您必须使用AsyncTask来解决“无法连接到数据库”错误。

这是使用AsynTask的代码，您还必须在onPostExecute方法中设置TextView的文本，如下所示：

 RetrievingDataFromDatabase retrievingTask; TextView resultView; String s; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); retrievingTask = new RetrievingDataFromDatabase(); retrievingTask.execute((Void) null); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; } public void getData(){ resultView = (TextView) findViewById(R.id.textView1); String result = ""; InputStream isr = null; try { HttpClient httpclient = new DefaultHttpClient(); HttpPost httppost = new HttpPost("http://HOSTNAME/FILENAME.php"); HttpResponse response = httpclient.execute(httppost); HttpEntity entity = response.getEntity(); isr = entity.getContent(); } catch(Exception e) { Log.e("log_tag", "Error in http connection " + e.toString()); resultView.setText("Couldnt connect to database"); } //converting to string try { BufferedReader reader = new BufferedReader(new InputStreamReader(isr, "iso-8859-1"), 8); StringBuilder sb = new StringBuilder(); String line = null; while ((line = reader.readLine()) != null) { sb.append(line + "\n"); } isr.close(); result = sb.toString(); } catch(Exception e) { Log.e("log_tag", "Error converting result " + e.toString()); } //parse data try { s = ""; JSONArray jArray = new JSONArray(result); for(int i = 0; i < jArray.length(); i++){ JSONObject json = jArray.getJSONObject(i); s = s + "St. ID" + json.getString("StId") + "\n " + json.getString("StName") + "\n" + json.getString("StMail"); } } catch(Exception e) { Log.e("Log_tage", "Error Parsing Data" + e.toString()); } } class RetrievingDataFromDatabase extends AsyncTask { @Override protected Boolean doInBackground(Void... params) { getData(); return null; } @Override protected void onPostExecute(Boolean result) { super.onPostExecute(result); resultView.setText(s); } } 

Answer 2

通过使用@Carlo的代码并编辑以下代码行来解决问题并检索数据：

 HttpPost httppost = new HttpPost("http://HOSTNAME/FILENAME.php"); 

至：

 HttpGet httppost = new HttpGet("http://HOSTNAME/FILENAME.php"); 

正如我的代码中提到的，我想从URL中检索数据而不是发布数据。

HttpPost>用于将数据提交到指定的资源。 HttpGet>用于从指定资源检索数据。

感谢你的帮助。