I am getting the following error message:
System.InvalidOperationException: ExecuteReader requires an open and available Connection. The connection's current state is Closed.
And here is my code:
public IDataReader ExecuteReader()
{
IDataReader reader = null;
try
{
this.Open();
reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
}
catch (Exception ex)
{
if (handleErrors)
strLastError = ex.Message;
else
throw;
}
catch
{
throw;
}
return reader;
}
Does anyone know how I can resolve this?
The Connection object that your SQLCommand is attached to has not been opened. You must open the connection before you can query.
Something like this:
private static void OpenSqlConnection(string connectionString)
{
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
var cmd = connection.CreateCommand();
// Do your command access here.
}
}
Related
I am trying to connect my Android Application to Postgres but seems not to work.
The Exception Message is: Exception while Connecting
This is my Code Behind,
private void Login_Clicked(object sender, EventArgs e)
{
DBInterface<DBLogicInput, DBLogicResult> dbLoginLogic = new DBLoginLogic();
DBLogicInput userInput = new DBLogicInput();
DBLogicResult DBResult = new DBLogicResult();
LoginModel useCredentials = new LoginModel()
{
userName = txtUsername.Text,
passWord = txtPassword.Text
};
userInput[typeof(LoginModel).FullName] = useCredentials;
try
{
DBResult = dbLoginLogic.DoProcess(userInput);
bool userExisting = DBResult.ResultCode != DBLogicResult.RESULT_CODE_ERR_DATA_NOT_EXIST;
if (userExisting)
{
Application.Current.MainPage = new NavigationPage(new IndexPage());
}
else
{
_ = DisplayAlert("Login Error", "User does not exist", "Ok");
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
This is the Class I created to connect the DB.
public abstract class DBLogic : DBInterface<DBLogicInput, DBLogicResult>
{
public string connectionString = "Server=localhost;Port=5432;User Id=postgres;Password=postgres;Database=proyektoNijuan";
public DBLogicResult DoProcess(DBLogicInput inOut)
{
//throw new NotImplementedException();
DBLogicResult result = default(DBLogicResult);
NpgsqlConnection connection = null;
NpgsqlTransaction transaction = null;
try {
connection = new NpgsqlConnection(connectionString);
if (connection.State != System.Data.ConnectionState.Open)
{
connection.Open();
}
transaction = connection.BeginTransaction();
result = Process(connection, inOut);
transaction.Commit();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
transaction.Rollback();
} finally {
if (connection != null)
{
connection.Close();
}
}
return result;
}
protected abstract DBLogicResult Process(NpgsqlConnection conn, DBLogicInput InOuT);
}
The error exists after the debugger hits the code connection.Open();.
Should I add a web services to connect the postgres to my android app built in xamarin forms?
I am only a beginner in Xamarin Forms. I am just trying to create a self application. And need a little help for me to learn a new platform in programming.
Thank you and Regards,
How to fix it?
Well, I think I am doing it wrong.
Maybe the Right way to Connect the PostgreSQL is to have a WEB API.
Calling that web API to the Xamarin forms.
I really don't know if it is correct, but I will give it a try.
I will update the correct answer after I finish the development of that WEB API so that other beginners will found this answer helpful.
I've a very simple application that adds messages to a queue and reads them using a MessagerListener.
Edit: I was testing this on a single instance of Artemis that had been setup as part of a two instance cluster on docker.
I want to create the ConnectionFactory once and reuse it for all producers and consumers in the application.
I have created the ConnectionFactory and stored it in a static variable (singleton) so it can be accessed from anywhere.
The aim is that the client use this shared connection factory to create a new connection when required.
However, I have noticed that doing this causes a "Failed to create session factory" when trying to create a new connection.
javax.jms.JMSException: Failed to create session factory
at org.apache.activemq.artemis.jms.client.ActiveMQConnectionFactory.createConnectionInternal(ActiveMQConnectionFactory.java:886)
at org.apache.activemq.artemis.jms.client.ActiveMQConnectionFactory.createConnection(ActiveMQConnectionFactory.java:299)
at com.test.artemistest.jms.QueueTest2.getMessagesFromQueue(QueueTest2.java:137)
at com.test.artemistest.jms.QueueTest2.access$000(QueueTest2.java:61)
at com.test.artemistest.jms.QueueTest2$1.run(QueueTest2.java:75)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:830)
Caused by: ActiveMQNotConnectedException[errorType=NOT_CONNECTED message=AMQ219007: Cannot connect to server(s). Tried with all available servers.]
at org.apache.activemq.artemis.core.client.impl.ServerLocatorImpl.createSessionFactory(ServerLocatorImpl.java:690)
at org.apache.activemq.artemis.jms.client.ActiveMQConnectionFactory.createConnectionInternal(ActiveMQConnectionFactory.java:884)
If I create a connection factory per call this error does not occur.
Doing this seems very inefficient.
I've recreated a similar issue below.
If I create the connection factory in the main method the error occurs.
However if created just before use in a method it works as expected.
If I add two listeners the error occurs even though they are in separate threads. Could it be linked to the fact the connections are not closed in the consumers but are in the producers?
Why is this the case and do you recommend sharing the connection factory?
Thanks
public class QueueTest2 {
private static boolean shutdown = false;
private static ConnectionFactory cf;
public static void main(String[] args) {
// uncomment below for error to occur
// QueueTest2.getConnectionFactory("localhost", 61616);
ExecutorService executor = Executors.newCachedThreadPool();
executor.execute(new Runnable() {
#Override
public void run() {
getMessagesFromQueue("localhost", 61616);
while (!shutdown) {
try {
Thread.sleep(1000L);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("getMessagesFromQueue shutdown");
}
});
addMessagesToQueue("localhost", 61616);
// uncommenting below also causes the issue
// executor.execute(new Runnable() {
// #Override
// public void run() {
// getMessagesFromQueue("localhost", 61616);
// while (!shutdown) {
// try {
// Thread.sleep(1000L);
// } catch (InterruptedException e) {
// e.printStackTrace();
// }
// }
// System.out.println("getMessagesFromQueue shutdown");
// }
// });
addMessagesToQueue("localhost", 61616);
try {
Thread.sleep(1000L);
} catch (InterruptedException e) {
e.printStackTrace();
}
shutdown = true;
executor.shutdownNow();
}
private static void addMessagesToQueue(String host, int port) {
ConnectionFactory cf2 = getConnectionFactory(host, port);
Connection connection = null;
Session sessionQueue = null;
try {
connection = cf2.createConnection("artemis", "password");
connection.setClientID("Producer");
sessionQueue = connection.createSession(false, Session.CLIENT_ACKNOWLEDGE);
Queue orderQueue = sessionQueue.createQueue("exampleQueue");
MessageProducer producerQueue = sessionQueue.createProducer(orderQueue);
connection.start();
// send 100 messages
for (int i = 0; i < 100; i++) {
TextMessage message = sessionQueue.createTextMessage("This is an order: " + i);
producerQueue.send(message);
}
} catch (JMSException ex) {
Logger.getLogger(QueueTest2.class.getName()).log(Level.SEVERE, null, ex);
} finally {
try {
if (sessionQueue != null) {
sessionQueue.close();
}
} catch (JMSException ex) {
Logger.getLogger(QueueTest2.class.getName()).log(Level.SEVERE, null, ex);
}
try {
if (connection != null) {
connection.close();
}
} catch (JMSException ex) {
Logger.getLogger(QueueTest2.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
private static void getMessagesFromQueue(String host, int port) {
ConnectionFactory cf2 = getConnectionFactory(host, port);
Connection connection2 = null;
Session sessionQueue2;
try {
connection2 = cf2.createConnection("artemis", "password");
connection2.setClientID("Consumer2");
sessionQueue2 = connection2.createSession(false, Session.CLIENT_ACKNOWLEDGE);
Queue orderQueue = sessionQueue2.createQueue("exampleQueue");
MessageConsumer consumerQueue = sessionQueue2.createConsumer(orderQueue);
consumerQueue.setMessageListener(new MessageHandlerTest2());
connection2.start();
Thread.sleep(5000);
} catch (JMSException ex) {
Logger.getLogger(QueueTest2.class.getName()).log(Level.SEVERE, null, ex);
} catch (InterruptedException ex) {
Logger.getLogger(QueueTest2.class.getName()).log(Level.SEVERE, null, ex);
}
}
private static ConnectionFactory getConnectionFactory(String host, int port) {
if (cf == null) {
Map<String, Object> connectionParams2 = new HashMap<String, Object>();
connectionParams2.put(TransportConstants.PORT_PROP_NAME, port);
connectionParams2.put(TransportConstants.HOST_PROP_NAME, host);
TransportConfiguration transportConfiguration = new TransportConfiguration(NettyConnectorFactory.class
.getName(), connectionParams2);
cf = ActiveMQJMSClient.createConnectionFactoryWithoutHA(JMSFactoryType.CF, transportConfiguration);
}
return cf;
}
}
class MessageHandlerTest2 implements MessageListener {
#Override
public void onMessage(Message message) {
try {
System.out.println("new message: " + ((TextMessage) message).getText());
message.acknowledge();
} catch (JMSException ex) {
Logger.getLogger(MessageHandlerTest2.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
I've run your code, but I don't see any errors. My guess is that there may be a timing issue related to concurrency. Try adding synchronized to your getConnectionFactory method since it can theoretically be called concurrently by multiple threads in your application, e.g.:
private synchronized static ConnectionFactory getConnectionFactory(String host, int port)
I have found a solution that works on a clustered environment and docker.
It involves using the "pooled-jms" connection pool. Something I had planned to use anyway.
Although it does not explain the issues I was seeing above, it is at least a work around until I can investigate further.
The "WARN: AMQ212064: Unable to receive cluster topology " mentioned above appears to have been a red herring as it went away as quickly as it appeared.
Is there a way to test below code.Here I am connecting to database with JNDI.I am new to mockito and not getting a way to test the same.
#SuppressWarnings("unused")
public Connection getJNDIConnection() {
Connection result = null;
try {
InitialContext initialContext = new InitialContext();
if (initialContext == null) {
LOGGER.info("JNDI problem. Cannot get InitialContext.");
}
DataSource datasource = (DataSource) initialContext.lookup(jndiName);
if (datasource != null) {
result = datasource.getConnection();
} else {
LOGGER.info("Failed to lookup datasource.");
}
} catch (NamingException ex) {
LOGGER.error("Cannot get connection: " + ex);
} catch (SQLException ex) {
LOGGER.error("Cannot get connection: " + ex);
}
return result;
}
Of course, you can to do it, but I think you should read the documentation yourself. The main points here is:
InitialContext initialContext = mock(InitialContext.class);
DataSource dataSource = mock(DataSource.class);
Connection expected = mock(Connection.class);
whenNew(InitialContext.class).withNoArguments().thenReturn(initialContext);
when(initialContext.lookup(jndiName)).thenReturn(dataSource);
when(initialContext.getConnection()).thenReturn(connection);
Connection result = intatnceOfCalss.getJNDIConnection();
assertSame("Should be equals", expected, result);
Also you should use PowerMock to mock constructors and static methods. To have deal with Logger, just add this code:
#BeforeClass
public static void setUpClass() {
mockStatic(LoggerFactory.class);
Logger logger = mock(Logger.class);
when(LoggerFactory.getLogger(ApplySqlFileIfExistsChange.class)).thenReturn(logger);
}
Don't forget about annotations:
#RunWith(PowerMockRunner.class)
#PrepareForTest({LoggerFactory.class})
Try to read this doc http://site.mockito.org/mockito/docs/current/org/mockito/Mockito.html
When /api/upload REST endpoint is accessed I have a UploadController that uses a service UploadService to upload a file to an ftp server with org.apache.commons.net.ftp.FTPClient. I would like to be able to send information back to the user if the ftp client was unable to connect or timed out, or successfully sent the file. I have some IOException handling, but I don't know how to turn that around and send it back to the front-end. Any help appreciated, thanks!
public void upload(InputStream inputStream) {
String filename = "file.txt"
client = new FTPClient();
try {
client.connect("ftpsite");
client.login("username", "password");
client.storeFile(filename, inputStream);
} catch (IOException ioe) {
ioe.printStackTrace();
} finally {
try {
if (inputStream!= null) {
inputStream.close();
}
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
return null;
}
You should throw a new Exception in your catch statement.
For example, you could create a RequestTimeoutException class:
#ResponseStatus(HttpStatus.REQUEST_TIMEOUT)
public class RequestTimeoutException extends RuntimeException { }
and then throw it when need be:
catch (IOException ioe) {
//do some logging while you're at it
throw new RequestTimeoutException();
}
This is the error which arises when I tried to debug an application under Visual C# 2010
I write that code to retrieve some rows from a database table, I already attached the two well known databases Pubs and Northwind to the db explorer, but the error remains
class Author
{
SqlConnection _pubConnection;
string _connString;
public Author()
{
_connString = "Data Source=./INSTANCE2;Initial Catalog=pubs;Integrated Security=True";
_pubConnection = new SqlConnection();
_pubConnection.ConnectionString = _connString;
}
public int CountAuthors()
{
try
{
SqlCommand pubCommand = new SqlCommand();
pubCommand.Connection = _pubConnection;
pubCommand.CommandText = "Select Count(au_id) from authors";
_pubConnection.Open();
return (int)pubCommand.ExecuteScalar();
}
catch (SqlException ex)
{
throw ex;
}
finally
{
if (_pubConnection != null)
{
_pubConnection.Close();
}
}
}
}
static void Main(string[] args)
{
try
{
Author author = new Author();
Console.WriteLine(author.CountAuthors());
Console.ReadLine();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
Console.ReadLine();
}
}
the Connection string isn't ok , i correct it and it works fine