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Tomcat doesn't sync with the mysql database

I'm currently working on a college project, and I'm creating a very simple e-commerce style website.
I'm using JDBC driver manager and connection pool for the connection to the db, while using Tomcat 9.0 as the container.
The problem is: when I modify some product through the website (let's say the amount available for example), the website doesn't always reflect the changes, while I can always see the data correctly in MySql Workbench.
It actually works one time out of two on the same query:
I run the query for the first time after the changes -> it shows the old value
I run the query for the second time after the changes -> it shows the new value
I run the query for the third time after the changes -> it shows the old value
And so on.
I've already tried to set caching off (from the query, using the SQL_NO_CACHE), but it didn't seem to solve the problem, I've tried to use Datasource instead, but it causes other problems that most likely I won't have the time to solve.
This is the connection pool file, which I think might be problem, I'm not that sure tho:
public class DriverManagerConnectionPool {
private static List<Connection> freeDbConnections;
static {
freeDbConnections = new LinkedList<Connection>();
try {
Class.forName("com.mysql.cj.jdbc.Driver");
} catch (ClassNotFoundException e) {
System.out.println("DB driver not found:"+ e.getMessage());
}
}
private static synchronized Connection createDBConnection() throws SQLException {
Connection newConnection = null;
String ip = "localhost";
String port = "3306";
String db = "storage";
String username = "root";
String password = "1234";
newConnection = DriverManager.getConnection("jdbc:mysql://"+ ip+":"+ port+"/"+db+"?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC", username, password);
newConnection.setAutoCommit(false);
return newConnection;
}
public static synchronized Connection getConnection() throws SQLException {
Connection connection;
if (!freeDbConnections.isEmpty()) {
connection = (Connection) freeDbConnections.get(0);
freeDbConnections.remove(0);
try {
if (connection.isClosed())
connection = getConnection();
} catch (SQLException e) {
connection.close();
connection = getConnection();
}
} else {
connection = createDBConnection();
}
return connection;
}
public static synchronized void releaseConnection(Connection connection) throws SQLException {
if(connection != null) freeDbConnections.add(connection);
}
}
I really hope you can help me, I haven't found any solution online!

I guess it is because of auto-commit is disabled. Please try using #Transactional or set auto-commit to true. You can also try to use db.commit after each statement.

As per your connection pool implementation, all connection in your pool seems to be auto committed false.
Please check you have properly committed the connection after executing the query or not.
So it might be the case that, when executing the query after changes with same connection it reflects those changes, done earlier and on other connections, old values are might get returned.

OrientDB. Connection leaks or just not closing connections

We have a large multithreaded Java EE application running on Wildfly 8.
We are using OrientDB 2.1.19.
And we have some problems with the connection leaks. At some point orient server stops responding and all threads working with db stuck on retrieving new connection.
Configuration is following:
OGlobalConfiguration.CLIENT_CONNECT_POOL_WAIT_TIMEOUT.setValue(5000);
OGlobalConfiguration.CLIENT_DB_RELEASE_WAIT_TIMEOUT.setValue(5000);
OGlobalConfiguration.CLIENT_CHANNEL_MAX_POOL.setValue(1000);
OGlobalConfiguration.DB_POOL_MIN.setValue(100);
OGlobalConfiguration.DB_POOL_MAX.setValue(5000);
OGlobalConfiguration.STORAGE_LOCK_TIMEOUT.setValue(5000);
OGlobalConfiguration.DB_POOL_IDLE_TIMEOUT.setValue(5000);
OGlobalConfiguration.DB_POOL_IDLE_CHECK_DELAY.setValue(1000);
OPartitionedDatabasePool we're getting thru OPartitionedDatabasePoolFactory
poolFactory = new OPartitionedDatabasePoolFactory();
documentPool = poolFactory.get(orientDBPath, username, password);
Then depending on our needs we are using ODatabaseDocumentTx or OObjectDatabaseTx using
documentPool.acquire();
Acquired ODatabaseDocumentTx or OObjectDatabaseTx we are passing to so called executor, which executes Runnable or Callable.
public void run(ORunnable<DB> oRunnable) {
// db is the private member of executor containing acquired db.
try {
//...
oRunnable.run(db);
//...
} catch (Exception e) {
} finally {
if(!db.isClosed()) {
db.close();
}
}
}
As you can see we are closing db in finally section, also we are fully detaching all documents recieved from db. But in some cases number of connections to DB is not dropping and after that we're getting following exception
2016-07-28 23:10:45,957 FINE [com.orientechnologies.orient.client.remote.ORemoteConnectionManager] (default task-46) Network connection pool is receiving a closed connection to reuse: discard it
2016-07-28 23:10:45,957 FINE [com.orientechnologies.orient.client.remote.ORemoteConnectionManager] (default task-46) Cannot unlock connection lock: java.lang.IllegalMonitorStateException
at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:155) [rt.jar:1.7.0_13]
at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1260) [rt.jar:1.7.0_13]
at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:460) [rt.jar:1.7.0_13]
at com.orientechnologies.common.concur.lock.OAdaptiveLock.unlock(OAdaptiveLock.java:123) [orientdb-core-2.1.19.jar:2.1.19]
at com.orientechnologies.orient.enterprise.channel.binary.OChannelBinaryAsynchClient.unlock(OChannelBinaryAsynchClient.java:371) [orientdb-enterprise-2.1.19.jar:2.1.19]
at com.orientechnologies.orient.client.remote.ORemoteConnectionManager.remove(ORemoteConnectionManager.java:128) [orientdb-client-2.1.19.jar:2.1.19]
at com.orientechnologies.orient.client.remote.ORemoteConnectionManager.release(ORemoteConnectionManager.java:119) [orientdb-client-2.1.19.jar:2.1.19]
at com.orientechnologies.orient.client.remote.OStorageRemote.endResponse(OStorageRemote.java:1643) [orientdb-client-2.1.19.jar:2.1.19]
at com.orientechnologies.orient.client.remote.OStorageRemote.command(OStorageRemote.java:1240) [orientdb-client-2.1.19.jar:2.1.19]
at com.orientechnologies.orient.client.remote.OStorageRemoteThread.command(OStorageRemoteThread.java:453) [orientdb-client-2.1.19.jar:2.1.19]
at com.orientechnologies.orient.core.sql.query.OSQLQuery.run(OSQLQuery.java:72) [orientdb-core-2.1.19.jar:2.1.19]
at com.orientechnologies.orient.core.sql.query.OSQLSynchQuery.run(OSQLSynchQuery.java:85) [orientdb-core-2.1.19.jar:2.1.19]
at com.orientechnologies.orient.core.query.OQueryAbstract.execute(OQueryAbstract.java:33) [orientdb-core-2.1.19.jar:2.1.19]
at com.orientechnologies.orient.core.db.document.ODatabaseDocumentTx.query(ODatabaseDocumentTx.java:717) [orientdb-core-2.1.19.jar:2.1.19]
Here is the piece of code for the exception above
ODocument storedSession = orient.onDocuments().call(new ODocCallable<ODocument>() {
#Override
public ODocument call(ODatabaseDocumentTx db) {
try {
List<ODocument> list = db.query(new OSQLSynchQuery<ODocument>("select from " + CLAZZ + " where storedSession_sessionID = ?"), sessionId);
if (list.isEmpty()){
return null;
}
return documentUnpin(list.get(0));
} catch (Exception e) {
// PersistentSession may not be in DB on request (for example in workspaces)
}
return null;
}
});
Any suggestions how to improve the situation with connections?
Thanks.

How to tell when there is a connection database issue?

I need to make a special treatment when a connection problem to the database is occurring like database server down and not an sql problem.
In the source code we can get various exceptions but which ones are belonging to the connection ones ?
We would like if this kind of problem occurs to make less logs.
EDITED
I have many methods that perform connection to the database but all get the session from the same method (initSession):
Here an example:
private Session initSession(HibernateUtil hibernateUtil) {
Session oSession = null;
try {
oSession = hibernateUtil.getSession();
} catch (Exception e) {
log.error("unable to log, Please check the details of your database");
}
return oSession;
}
public List findAlerts(int pFirstLine, int pNbElement) throws AnalyzerException {
List oAlerts = new ArrayList();
Session oSession = initSession(lHibernateUtil);
try {
oAlerts = AlertFinders.instance().findAlertByStatus(oSession, false, pFirstLine, pNbElement);
Iterator iterAlerts = oAlerts.iterator();
while (iterAlerts.hasNext()) {
...
}
} catch (UnableToLocateObjectException eU) {
throw new AnalyzerException(eU.getMessageSource(), eU.getClassNameSource(), eU.getMethodSource(), eU);
} finally {
oSession.close();
}
return oAlerts;
}

Multiple possible ways.
Use Java Connection isValid method.
Use connection pool - All major connection
pools support this functionality (including c3p0 and dbcp).They can
throw SQLException has getErrorCode() and getSQLState() methods
Write Java code & poll frequently - sample code below
Run arguments sample: jdbc:oracle:thin:#localhost:1521:XE system mypassword123 oracle.jdbc.driver.OracleDriver
public class DbConnCheck {
public static void main(String[] args) throws Exception {
String url = args[0];
String username = args[1];
String password = args[2];
String driver = args[3];
Class.forName(driver);
Connection conn = DriverManager.getConnection(url, username, password);
try {
Statement statement = conn.createStatement();
ResultSet rs = statement.executeQuery("SELECT SYSDATE FROM DUAL");
while(rs.next()) {
System.out.println(rs.getObject(1));
}
} finally {
conn.close();
}
}
}
Edit : Adding details on hibernate part
Not done in Hibernate but to be precise you can check in connection pool configuration.
If using c3p0 then check how you can best use setting like idle_test_period, preferredTestQuery and testConnectionOnCheckout;
If using dbcp then validationQuery can do the job.
If you want to use c3p0 with Hibernate and Spring check this link

Lock wait timeout exceeded with Hibernate and MySQL (using play framework)

In my web application I'm using Stateless sessions with Hibernate to have better performances on my inserts and updates.
It was working fine with H2 database (the one used in play framework in dev mode).
But when I test it with MySQL I get the following exception :
ERROR ~ Lock wait timeout exceeded; try restarting transaction
ERROR ~ HHH000315: Exception executing batch [Lock wait timeout exceeded; try restarting transaction]
Here is the code :
public static void update() {
Session session = (Session) JPA.em().getDelegate();
StatelessSession stateless = this.session.getSessionFactory().openStatelessSession();
try {
stateless.beginTransaction();
// Fetch all products
{
List<ProductType> list = ProductType.retrieveAllWithHistory();
for (ProductType pt : list) {
updatePrice(pt, stateless);
}
}
// Fetch all raw materials
{
List<RawMaterialType> list = RawMaterialType.retrieveAllWithHistory();
for (RawMaterialType rm : list) {
updatePrice(rm, stateless);
}
}
} catch (Exception ex) {
play.Logger.error(ex.getMessage());
ExceptionLog.log(ex, Thread.currentThread());
} finally {
stateless.getTransaction().commit();
stateless.close();
}
}
private static void updatePrice(ProductType pt, StatelessSession stateless) {
pt.priceDelta = computeDelta();
pt.unitPrice = computePrice();
stateless.update(pt);
PriceHistory ph = new PriceHistory(pt, price);
stateless.insert(ph);
}
private static void updatePrice(RawMaterialType rm, StatelessSession stateless) {
rm.priceDelta = computeDelta();
rm.unitPrice = computePrice();
stateless.update(rm);
PriceHistory ph = new GoodPriceHistory(rm, price);
stateless.insert(ph);
}
In this example I have 3 simple Entities (ProductType, RawMaterialType and PriceHistory).
computeDelta and computePrice are just algorithm functions with no DB stuff.
retrieveAllWithHistory functions are functions that fetch some data from the database using Play framework model functions.
So, this code retrieves some data, edit some, create new one and finally save everything.
Why have I a lock exception with MySQL and no exception with H2 ?

I'm not sure why you have a commit in a finally block. Give this structure a try:
try {
factory.getCurrentSession().beginTransaction();
factory.getCurrentSession().getTransaction().commit();
} catch (RuntimeException e) {
factory.getCurrentSession().getTransaction().rollback();
throw e; // or display error message
}
Also, it might be helpful for you to check this documentation.

Java connecting to multiple databases

I am creating a java application that connects to multiple databases. A user will be able to select the database they want to connect to from a drop down box.
The program then connects to the database by passing the name to a method that creates an initial context so it can talk with an oracle web logic data source.
public class dbMainConnection {
private static dbMainConnection conn = null;
private static java.sql.Connection dbConn = null;
private static javax.sql.DataSource ds = null;
private static Logger log = LoggerUtil.getLogger();
private dbMainConnection(String database) {
try {
Context ctx = new InitialContext();
if (ctx == null) {
log.info("JDNI Problem, cannot get InitialContext");
}
database = "jdbc/" + database;
log.info("This is the database string in DBMainConnection" + database);
ds = (javax.sql.DataSource) ctx.lookup (database);
} catch (Exception ex) {
log.error("eMTSLogin: Error in dbMainConnection while connecting to the database : " + database, ex);
}
}
public Connection getConnection() {
try {
return ds.getConnection();
} catch (Exception ex) {
log.error("Error in main getConnection while connecting to the database : ", ex);
return null;
}
}
public static dbMainConnection getInstance(String database) {
if (dbConn == null) {
conn = new dbMainConnection(database);
}
return conn;
}
public void freeConnection(Connection c) {
try {
c.close();
log.info(c + " is now closed");
} catch (SQLException sqle) {
log.error("Error in main freeConnection : ", sqle);
}
}
}
My problem is what happens if say someone forgets to create the data source for the database but they still add it to the drop down box? Right now what happens is if I try and connect to a database that doesn't have a data source it errors saying it cannot get a connection. Which is what I want but if I connect to a database that does have a data source first, which works, then try and connect to the database that doesn't have a data source, again it errors with
javax.naming.NameNotFoundException: Unable to resolve 'jdbc.peterson'. Resolved 'jdbc'; remaining name 'peterson'.
Which again I would expect but what is confusing me is it then grabs the last good connection which is for a different database and process everything as if nothing happened.
Anyone know why that is? Is weblogic caching the connection or something as a fail safe? Is it a bad idea to create connections this way?

You're storing a unique datasource (and connection, and dbMainConnection) in a static variable of your class. Each time someone asks for a datasource, you replace the previous one by the new one. If an exception occurs while getting a datasource from JNDI, the static datasource stays as it is. You should not store anything in a static variable. Since your dbMainConnection class is constructed with the name of a database, and there are several database names, it makes no sense to make it a singleton.
Just use the following code to access the datasource:
public final class DataSourceUtil {
/**
* Private constructor to prevent unnecessary instantiations
*/
private DataSourceUtil() {
}
public static DataSource getDataSource(String name) {
try {
Context ctx = new InitialContext();
String database = "jdbc/" + name;
return (javax.sql.DataSource) ctx.lookup (database);
}
catch (NamingException e) {
throw new IllegalStateException("Error accessing JNDI and getting the database named " + name);
}
}
}
And let the callers get a connection from the datasource and close it when they have finished using it.

You're catching JNDI exception upon lookup of the nonexistent datasource but your singleton still keeps the reference to previously looked up datasource. As A.B. Cade says, null reference to ds upon exception, or even before that.
On a more general note, perhaps using Singleton is not the best idea.