I have a support website that I would like to show some stats gathered from another Java app via JMX. We have noticed the support app sometimes cannot get the stats after the other app has been restarted. I guess this is because the support app has opening a JMX connection to the other app and keeps hold of it. Then every time you go to the page to display the JMX stats it tries to gather them using the connection and it fails.
My question is, is it better to have a single JMX connection and try and work out when we should reconnect it?
Or each time we load the page with JMX stats on it should we create a new JMX connection then close it once we have the values we need?
As per my knowledge,
JMX connections are RMI Connector objects and hence can be held in the client app. + use a heartbeat approach to reconnect.
This way we can avoid overhead of re-establishing RMI connections which are not light weight.
Refer: javax.management.remote.rmi.RMIConnector
We didn't end up using a heartbeat but after reading Girish's answer came up with the following
public class JmxMetricsRetriever {
private final JMXServiceURL jmxUrl;
private final Map<String, Object> env;
private MBeanServerConnection connection;
private JmxMetricsRetriever(JMXServiceURL jmxUrl, Map<String, Object> env) {
this.jmxUrl = jmxUrl;
this.env = env;
reconnect();
}
public synchronized Object getAttributeValue(String jmxObjectName, String attributeName) {
try {
if (connection == null) {
reconnect();
}
try {
return getAttributeValuePrivate(jmxObjectName, attributeName);
} catch (ConnectException exc) {
//This is to reconnect after the Server has been restarted.
reconnect();
return getAttributeValuePrivate(jmxObjectName, attributeName);
}
} catch (MalformedObjectNameException |
AttributeNotFoundException |
MBeanException |
ReflectionException |
InstanceNotFoundException |
IOException ex) {
throw new RuntimeException(ex);
}
}
private synchronized Object getAttributeValuePrivate(String jmxObjectName, String attributeName) throws MalformedObjectNameException, MBeanException, AttributeNotFoundException, InstanceNotFoundException, ReflectionException, IOException {
ObjectName replication = new ObjectName(jmxObjectName);
return connection.getAttribute(replication, attributeName);
}
private synchronized void reconnect() {
logger.info(String.format("Reconnecting to [%s] via JMX", jmxUrl.toString()));
try {
JMXConnector jmxConnector = JMXConnectorFactory.connect(jmxUrl, env);
this.connection = jmxConnector.getMBeanServerConnection();
jmxConnector.connect();
} catch (IOException e) {
//Log something but don't throw an exception otherwise our app will fail to start.
}
}
public static JmxMetricsRetriever build(String url, String port, String user, String password) {
try {
JMXServiceURL jmxUrl = new JMXServiceURL("service:jmx:rmi:///jndi/rmi://" + url + ":" + port + "/jmxrmi");
Map<String, Object> env = new HashMap<>();
env.put(JMXConnector.CREDENTIALS, new String[]{user, password});
return new JmxMetricsRetriever(jmxUrl, env);
} catch (MalformedURLException ex) {
throw new RuntimeException(ex);
}
}
}
When we start our app we try and create a JMX connect an hold on to it. Every time we get a JMX attribute we check the connection has been created (might not of been if the server we are connecting to was not up when we started our service). Then try and retrieve our attribute. If it failed try and reconnect and get the attribute value. We could not find a better way to test of a JMX connect was still usable so had to catch the exception.
Related
Heading ##I have problem with my java application with database in mySQL and swing GUI.
When I've used localhost everything worked properly. But now I would like to share project with my friend and we decided to use server hosting.
And here is a problem:
Now application works very slow, after pressing a button I have to wait a few seconds for the program to respond. Also the connection is lost from time to time. I have no idea where can I find reason for the problem... Do somebody now what is the reason of this problem?
private static Connection connection = null;
Boolean error = false;
private static String jdbcURL = "jdbc:mysql://host_name:3306/db_name";
private static String user = "user";
private static String password = "password";
MakeConnection(Connection connection) throws SQLException{
this.connection = connection;
try {
getConnection();
System.out.print("Connected to the data base in MakeConnection");
}
catch(Exception e) {
error = true;
System.out.print("Error in connection in MakeConnection consturctor" + e.getMessage());
}
finally{
if(connection!=null) connection.close();
if(error) System.out.print("Problem with connection");
else System.out.print("Program finished");
}
}
public Connection getConnection() throws SQLException {
try {
Class.forName("com.mysql.cj.jdbc.Driver");
connection = DriverManager.getConnection(jdbcURL,user,password);
} catch (Exception e) {
e.printStackTrace();
}
return connection;
}
}
Also sometimes application shows this error:
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
I don't see any problem in your code. The problem is probably with your server hosting. You should check the country of the host provider and measure the time required to send a request to the server. Also you should use logger instead of System.out.println so you can examine required time for actions like db access, application logic and find a bottleneck.
I'm creating an app which generates a CSV file and some PDFs. I want my app to send those files to a server via FTPS protocol.
I'm using Apache Commons Net FTP library and it was perfectly working when I had "Require TLS session resumption on data connection when using PORT P" unchecked, but since I enabled it I can't send my files.
An error appeared :
450 TLS session of data connection has not resumed or the session does not match the control connection.
After some researches on this site I have overriden _prepareDataSocket_ in order to overcome this problem but now it just creates empty files on the server.
There is my overriden function :
#Override
protected void _prepareDataSocket_(final Socket socket) throws IOException {
if (socket instanceof SSLSocket) {
// Control socket is SSL
final SSLSession session = ((SSLSocket) _socket_).getSession();
if (session.isValid()) {
final SSLSessionContext context = session.getSessionContext();
try {
final Field sessionHostPortCache = context.getClass().getDeclaredField("sessionHostPortCache");
sessionHostPortCache.setAccessible(true);
final Object cache = sessionHostPortCache.get(context);
final Method method = cache.getClass().getDeclaredMethod("put", Object.class, Object.class);
method.setAccessible(true);
method.invoke(cache, String
.format("%s:%s", socket.getInetAddress().getHostName(), String.valueOf(socket.getPort()))
.toLowerCase(Locale.ROOT), session);
method.invoke(cache, String
.format("%s:%s", socket.getInetAddress().getHostAddress(), String.valueOf(socket.getPort()))
.toLowerCase(Locale.ROOT), session);
} catch (NoSuchFieldException e) {
throw new IOException(e);
} catch (Exception e) {
throw new IOException(e);
}
} else {
throw new IOException("Invalid SSL Session");
}
}
}
and this is what FileZilla Server displays:
FileZilla Response
will this answer on another forum help?
http://forum.rebex.net/5673/450-error-connecting-to-ftp-requiring-explicit-ftp-over-tls
I'm looking for best way to check connection to Mongo DB.
Situation: client makes request (api) to server. And server returns status of all databases.
What the best way to do it?
I use this:
Builder o = MongoClientOptions.builder().connectTimeout(3000);
MongoClient mongo = new MongoClient(new ServerAddress("192.168.0.1", 3001), o.build());
try {
mongo.getAddress();
} catch (Exception e) {
System.out.println("Mongo is down");
mongo.close();
return;
}
In Java MongoDriver 3.3.0 use ServerMonitorListener to determine whether server is up and connected or not.
Here is the example code,
public class ServerConnection implements ServerMonitorListener {
private MongoClient client;
public ServerConnection(){
try {
MongoClientOptions clientOptions = new MongoClientOptions.Builder()
.addServerMonitorListener(this)
.build();
client = new MongoClient(new ServerAddress("localhost", 27017), clientOptions);
} catch (Exception ex) {
}
}
#Override
public void serverHearbeatStarted(ServerHeartbeatStartedEvent serverHeartbeatStartedEvent) {
// Ping Started
}
#Override
public void serverHeartbeatSucceeded(ServerHeartbeatSucceededEvent serverHeartbeatSucceededEvent) {
// Ping Succeed, Connected to server
}
#Override
public void serverHeartbeatFailed(ServerHeartbeatFailedEvent serverHeartbeatFailedEvent) {
// Ping failed, server down or connection lost
}
}
The ping command is a no-op used to test whether a server is responding to commands. This command will return immediately even if the server is write-locked:
try{
DBObject ping = new BasicDBObject("ping", "1");
mongoTemplate.getDb().getMongo().getDB("DATABASE NAME"").command(ping);
} catch (Exception exp){
// MongoDb is down..
}
Use MongoClient for Java, all the info you need is here...
http://docs.mongodb.org/ecosystem/tutorial/getting-started-with-java-driver/
If I understand your question correctly you want to get state returned via a web service call. You can write a function that invokes db.serverStatus() and have it return the data. Check out the documentation here:
Monitoring for MongoDB
I'm working on a webapp where i manually create my DataSource. (also see my other question why: How to use Spring to manage connection to multiple databases) because I need to connect to other databases (dev, prod, qa, test).
Now I have solved it to choose and switch between databases. But if a user logs out of my app. He wants to try to connect to an other database. He is still connected to the same datasource because at runtime the myDs is not null. How can I properly dispose of this Datasource when user logs out? I don't want the user to create the datasource every time he queries the database.
private DataSource createDataSource(Environment e) {
OracleDataSource ds = null;
String url = null;
try {
if (myDs != null) {
logger.info("myDs connection: " + etmetaDs.getConnection().getMetaData().getURL());
url = myDs.getConnection().getMetaData().getURL();
}
} catch (SQLException exc) {
// TODO Auto-generated catch block
exc.printStackTrace();
}
if (myDs == null) {
try {
ds = new OracleDataSource();
} catch (SQLException ex) {
ex.printStackTrace();
}
ds.setDriverType("oracle.jdbc.OracleDriver");
ds.setURL(e.getUrl());
try {
Cryptographer c = new Cryptographer();
ds.setUser(c.decrypt(e.getUsername()));
ds.setPassword(c.decrypt(e.getPassword()));
} catch (CryptographyException ex) {
logger.error("Failed to connect to my environment [" + e.getName() + "]");
ex.printStackTrace();
return null;
}
logger.info("Connecting to my environment [" + e.getName() + "]");
myDs = ds;
} else if (url.equals(e.getUrl())) {
} else {
}
return myDs;
}
If you read the answer of Reza in you other question you can see how to create multiple DataSource.
I think here that the problem is not the DataSource but the way you store information in your code. I suppose that your etmetaDs is shared but all your users, so dispose it when a user log out (= set it to null) is not the good option.
What you have to do, is to maintain the status of the connection for each user. And when a user log off, you can reset is status in order to obtain a new connection the next time it connects.
Update: There are many way to achieve this. I give here an example of what I imagine, but you have to adapt it to your needs. Suppose that you have a UserData object that holds information :
public class UserData
{
String id;
String name;
String database;
}
You may have in your application a dropdown with the name of the database (dev, test, ...) with an empty first item. When the user selects a database, you get the connection with createDataSource(). If it already exists you returns the DataSource else you create a new one. When your user disconnect (or when the user log on), you set the database to "" to force him to select the database in the dropdown. There is no need to reset the datasource.
The code below does NOT work:
Cause:
I assume I tracked down the cause to:
http://community.jboss.org/thread/150988
=> This article says that HornetQ uses Weak References.
My Question:
Why does the code not run? (I have this code running with a slight different implementation, but the code blow fails repeatedly). My only guess is, that the
following references:
private Connection connection = null;
private Session session = null;
private MessageProducer producer = null;
are not regarded as strong references? (And this leads to the fact that the garbage collector removes the objects... But way arent they strong references?
Or is there another problem with the code (as said the code runs fine if I copy everything into one single method. But if I use the Singleton approach below the code does not work...) Another assumption was that it might have to do with ThreadLocal stuff, but I am using only a single thread...
The Code not working (stripped down):
public class JMSMessageSenderTest {
private static final Logger logger = Logger.getLogger(JMSMessageSenderTest.class);
private static JMSMessageSenderTest instance;
private Connection connection = null;
private Session session = null;
private MessageProducer producer = null;
private JMSMessageSenderTest() {
super();
}
public static JMSMessageSenderTest getInstance() throws JMSException {
if (instance==null) {
synchronized(JMSMessageSenderTest.class) {
if (instance==null) {
JMSMessageSenderTest instanceTmp = new JMSMessageSenderTest();
instanceTmp.initializeJMSConnectionFactory();
instance = instanceTmp;
}
} }
return instance;
}
private void createConnectionSessionQueueProducer() throws Exception {
try {
Queue queue = HornetQJMSClient.createQueue("testQueue");
connection = initializeJMSConnectionFactory();
session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
producer = session.createProducer(queue);
connection.start();
} catch (Exception e) {
cleanupAfterError();
throw e;
}
}
private void cleanupAfterError() {
if (connection != null){
try{
connection.close();
}catch(JMSException jmse) {
logger.error("Closing JMS Connection Failed",jmse);
}
}
session = null;
producer = null;
}
public synchronized void sendRequest(String url) throws Exception {
if (connection==null) {
createConnectionSessionQueueProducer();
}
try {
//HERE THE EXCEPTION IS THROWN, at least when debugging
TextMessage textMessage = session.createTextMessage(url);
producer.send(textMessage);
} catch (Exception e) {
cleanupAfterError();
throw e;
}
}
private Connection initializeJMSConnectionFactory() throws JMSException{
Configuration configuration = ConfigurationFactory.getConfiguration(null, null);
Map<String, Object> connectionParams = new HashMap<String, Object>();
connectionParams.put(org.hornetq.core.remoting.impl.netty.TransportConstants.PORT_PROP_NAME, 5445);
connectionParams.put(org.hornetq.core.remoting.impl.netty.TransportConstants.HOST_PROP_NAME, "localhost");
TransportConfiguration transportConfiguration = new TransportConfiguration(NettyConnectorFactory.class.getName(), connectionParams);
ConnectionFactory connectionFactory = (ConnectionFactory) HornetQJMSClient.createConnectionFactoryWithoutHA(JMSFactoryType.CF, transportConfiguration);
// return connectionFactory.createConnection(login, password);
return connectionFactory.createConnection();
}
/**
* Orderly shutdown of all resources.
*/
public void shutdown() {
cleanupAfterError();
}
}
TestCode to run the code above
JMSMessageSenderTest jmsMessageSender = JMSMessageSenderTest.getInstance();
jmsMessageSender.sendRequest("www.example.com)");
jmsMessageSender.shutdown();
Gives the following error:
I'm closing a JMS connection you left open. Please make sure you close all JMS connections explicitly before letting them go out of scope!
The JMS connection you didn't close was created here:
java.lang.Exception
at org.hornetq.jms.client.HornetQConnection.<init>(HornetQConnection.java:152)
at org.hornetq.jms.client.HornetQConnectionFactory.createConnectionInternal(HornetQConnectionFactory.java:662)
at org.hornetq.jms.client.HornetQConnectionFactory.createConnection(HornetQConnectionFactory.java:121)
Solution:
1.) You also have to Keep a reference to the ConnectionFactory (see the answer from Clebert below)
private ConnectionFactory factory = null;
2.) AND this code contains a severe hidden bug (that is not so easy to spot):
I initialized the Connection in the Constructor as well as in the createConnectionSessionQueueProducer() method. It will therefore override the old value and (as it is a Ressource that needs to be closed) will lead to a stale connection that HornetQ then will close and will then throw the error.
Thanks very very much! Markus
HornetQ will close the connection factory when the connection factory is released.
You need to hold a reference for the connection factory.
I also have similar issues. But it is not supposed to crash . Your implementation looks good. But only thing is that you are not closing the JMS connection , which in turn is getting closed by the hornetQ gc.
One thing probably wrong with the code is that you are calling cleanupAfterError() only after an exception. You should call the same method also after you have posted a message and a JMS connection is lying idle . Since you are just opening a connection to post a message and then not closing that connection unless an exception happens , Hornetq GC is finding that object and removing it while throwing this error.
Let me know if I missed something