Hibernate loses connection

Question

I am using hibernate to connect my mysql database and perform transactions.

I am using a single SessionFactory throughout the application and i don't have other connections to the database, yet, i am receiving the exception below:

java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
    at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:3008)
    at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3466)
    ... 21 common frames omitted
Wrapped by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 526 milliseconds ago.  The last packet sent successfully to the server was 1 milliseconds ago.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:989)
    at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3556)
    at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3456)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3897)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2524)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2677)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2545)
    at com.mysql.jdbc.ConnectionImpl.setAutoCommit(ConnectionImpl.java:4842)
    at org.hibernate.engine.jdbc.connections.internal.PooledConnections.poll(PooledConnections.java:84)
    at org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl.getConnection(DriverManagerConnectionProviderImpl.java:186)
    at org.hibernate.internal.NonContextualJdbcConnectionAccess.obtainConnection(NonContextualJdbcConnectionAccess.java:35)
    at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.acquireConnectionIfNeeded(LogicalConnectionManagedImpl.java:99)
    ... 11 common frames omitted
Wrapped by: org.hibernate.exception.JDBCConnectionException: Unable to acquire JDBC Connection
    at org.hibernate.exception.internal.SQLStateConversionDelegate.convert(SQLStateConversionDelegate.java:115)
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:111)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:97)
    at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.acquireConnectionIfNeeded(LogicalConnectionManagedImpl.java:102)
    at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.getPhysicalConnection(LogicalConnectionManagedImpl.java:129)
    at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.getConnectionForTransactionManagement(LogicalConnectionManagedImpl.java:247)
    at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.begin(LogicalConnectionManagedImpl.java:254)
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl$TransactionDriverControlImpl.begin(JdbcResourceLocalTransactionCoordinatorImpl.java:203)
    at org.hibernate.engine.transaction.internal.TransactionImpl.begin(TransactionImpl.java:56)
    at org.hibernate.internal.AbstractSharedSessionContract.beginTransaction(AbstractSharedSessionContract.java:387)
    at com.kitaplist.common.book.dao.HibernateBookDao.find(HibernateBookDao.java:56)
    at com.kitaplist.common.Collector.lambda$collectMetaBooksAndNewBooks$1(Collector.java:137)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

This is how i create my SessionFactory:

public static SessionFactory getSessionFactory() {

    if (sessionFactory == null) {
        sessionFactory = new Configuration()
                .configure()
                .addAnnotatedClass(Seller.class)
                .addAnnotatedClass(Book.class)
                .buildSessionFactory();
    }

    return sessionFactory;
}

and here is the function that I use in my BookDao:

@Override
public void save(Book book) {
    Session session = sessionFactory.openSession();
    Transaction tx = session.beginTransaction();
    try {
        session.save(book);
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try {
            tx.commit();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            session.close();
        }

    }
}

my application is a crawler crawls a book object from web and saves the object to the database through the above save function. I couldn't find the reason behind this exception.

on the command console, i can see that the connection is re-established after it is lost, here :

SLF4J: A number (289) of logging calls during the initialization phase have been intercepted and are
SLF4J: now being replayed. These are subject to the filtering rules of the underlying logging system.
SLF4J: See also http://www.slf4j.org/codes.html#replay
Wed Mar 14 16:36:29 UTC 2018 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Wed Mar 14 16:36:29 UTC 2018 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Wed Mar 14 16:36:30 UTC 2018 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Wed Mar 14 16:36:29 UTC 2018 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.


Wed Mar 14 16:47:14 UTC 2018 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.

Wed Mar 14 16:47:17 UTC 2018 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.

I would appreciate any help.

Answer 1

You can use

sessionFactory.isClosed();

to determine if the connection is still open. Replace your getSessionFactory() method like this.

public static SessionFactory getSessionFactory() {

    if (sessionFactory == null || sessionFactory.isClosed()) {
        sessionFactory = new Configuration()
                .configure()
                .addAnnotatedClass(Seller.class)
                .addAnnotatedClass(Book.class)
                .buildSessionFactory();
    }

    return sessionFactory;
}

Answer 2

   at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:989)
    at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3556)
    at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3456)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3897)

From your stacktrace it seems hibernate is not able to obtain connections from database as db server has gone away

    // Check return value, if we get a java.io.EOFException, the server has gone away. We'll pass it on up the exception chain and let someone higher up
   // decide what to do (barf, reconnect, etc).

Check source here:
http://grepcode.com/file/repo1.maven.org/maven2/mysql/mysql-connector-java/5.1.36/com/mysql/jdbc/MysqlIO.java#3774

Possible explaination :
The problem seems at database server side not in your code. You may need to tweak your mysql server settings and problem will be solved. The data you are sending is larger than the packet that is sent over the network to the database.

Causes and solutions :
https://dev.mysql.com/doc/refman/5.7/en/gone-away.html
http://befused.com/mysql/server-has-gone-away

Other Solutions:
in my.cnf file of mysql add following settings

[mysqld]
max_allowed_packet=256M