Question

我正在尝试执行以下代码，以便使用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 20：10：35.057：E / log_tag（5323）：http connectionandroid.os.NetworkOnMainThreadException错误

11-14 20：10：35.057：E / log_tag（5323）：转换resultjava.lang.NullPointerException时出错：lock == null

11-14 20：10：35.057：E / Log_tage（5323）：错误解析Dataorg.json.JSONException：字符0处的输入结束

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

PHP文件：

   <?php 
$con = mysql_connect("HOST","USERNAME","PASSWORD");
if (!$con)
    {
    die('Could not Connect:'. mysql_error());
    }
mysql_select_db("database_name",$con);

$result = mysql_query("SELECT * FROM table_name");

while($row = mysql_fetch_assoc($result))
    {
       $output[]=$row;
    }

print(json_encode($output));
mysql_close($con);
?>

请帮助。

Answer 1

HttpPost网址没有特定的格式，它与网络服务中提供的网址相同。

您必须使用AsyncTask来解决“无法连接到数据库”错误。

以下是使用AsynTask的代码，您还必须在TextView方法中设置onPostExecute的文字，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<Void, Void, Boolean> {

    @Override
    protected Boolean doInBackground(Void... params) {
        getData();
        return null;
    }

    @Override
    protected void onPostExecute(Boolean result) {
        super.onPostExecute(result);
        resultView.setText(s);
    }
}

Answer 2

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");

为：

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

如我的代码中所述，我想从URL中检索数据而不是发布数据。

HttpPost＆gt;用于将数据提交到指定的资源。 HttpGet＆gt;用于从指定资源中检索数据。

感谢大家的帮助。

无法使用Android连接到数据库

2 个答案: