java - 与数据库的连接卡在 asynctask 中

Question

我有一个连接到sql server的代码，在主线程上运行它时它工作得很好，但是由于连接时线程卡住，我决定将代码放入异步任务中。现在它卡在了connection.getConnection(connectionURL)上..有人知道为什么吗？

public class ConnectionClass extends AsyncTask<Void,Void,Void> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        progressDialog.setCancelable(false);
        progressDialog.setTitle(getString(R.string.establishing_cnxtn));
        progressDialog.setMessage(getString(R.string.connecting));
        progressDialog.show();
    }

    @Override
    protected Void doInBackground(Void... voids) {


        connection = DatabaseHandler.getConnection(MainActivity.this);
        return null;

    }


    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        progressDialog.dismiss();

        if (connection == null)
            Snackbar.make(layout, R.string.could_not_connect, Snackbar.LENGTH_LONG).show();

        else {
            try {
                updateUI();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

这是数据库代码，但我知道问题不在于这段代码......

 static Connection getConnection(Context context)
{
    SharedPreferences sharedPreferences = context.getSharedPreferences("ip",MODE_PRIVATE);
    //ip = sharedPreferences.getString("ip","");

    ip = "PC-HASSANSHOUMA"; //database ip
    db = "***"; //database name
    un = "***"; //username to connect to db
    pass = "***"; //password to connect to db
    connectionURL = null;
    port = "1433";

    Log.i("jsbnkjnbsjkdjk","dfdfdfdfdfd");

    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);

    Log.i("bjhbdjs","dfdfdfdfdfd");
    if(connection == null)
    {
        try
        {
            Class.forName("net.sourceforge.jtds.jdbc.Driver");
            Log.i("nbkjnjk","dfdfdfdfdfd");
            connectionURL = "jdbc:jtds:sqlserver://"+"192.168.0.112"+"/"+db+";instance=SQL2014;user="+un+";"+"password="+pass+";";
            Log.i("kjhknklnkl","dfdfdfdfdfd");
            connection =  DriverManager.getConnection(connectionURL);
            Log.i("njknjknj","dfdfdfdfdfd");
            statement = connection.createStatement();
            Log.i("klklllk","dfdfdfdfdfd");

        } catch (ClassNotFoundException | SQLException e) {
            Log.i("nklnkl54564","dfdfdfdfdfd");
            e.printStackTrace();
        }
    }



    return connection;

}

Answer 1

protected String doInBackground(String... params) {
        final String SERVICE_URL = params[0]  ;
        ConnectivityManager connMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
        if (networkInfo != null && networkInfo.isConnected()) {
            try {
                String result = downloadUrl(SERVICE_URL,params[1],params[2]); 
                z= result;
            } catch (Exception e) {
                z = "error";
                onPostExecute(z);
            }
        }
        return z;
    }

并且在async的downloadUrl方法中:这是一个自定义方法

private String downloadUrl(String urlString,String iOutputFile,String iOutputPath) throws IOException {
        InputStream inStream = null;
        int len = 1000000; //Is not used
        try {
            URL url = new URL(urlString);
            HttpsURLConnection conn = (HttpsURLConnection) url.openConnection();
            conn.setReadTimeout(10000);  // milliseconds
            conn.setConnectTimeout(15000);  // milliseconds
            conn.setRequestMethod("GET");
            conn.setDoInput(true);

            conn.connect();
            int response = conn.getResponseCode();

            long lenghtOfFile = conn.getContentLength();
            inStream = conn.getInputStream();
            return saveIt(inStream,iOutputFile,iOutputPath,lenghtOfFile);

        }
        catch (IOException e)
        {

            return e.getMessage();
        }
        finally {
            if (inStream != null) {
                inStream.close();
            }
        }
    }

saveit 也是执行任务后的自定义方法...saveit 是异步类的私有(private)方法(用于下载后处理...)。在此示例中，我从服务器获取了一个文件，然后将其保存在手机中。

在调用 asynctask 实例时:

new GetGedFileFromServer().execute(file_url4Download,file_Name4Save,file_Path4Save);

我的 asyncTask 的名称是 GetGedFileFromServer()

您唯一要做的就是创建一个字符串呈现 file_url4Download ...最后，这只是您想要发送文件或从服务器上分配的 sql 服务器获取数据的示例代码或...。您可以自定义处理对话框的 pre 和 post 方法...