一段时间后失去与MySQL的连接，而不是重新连接

Question

I'm developing a standalone server which uses JPA+Hibernate to access a MySQL database.

When I start the server, everything is working fine. However, after a while (usually the next morning, if I start it in the afternoon) it will stop working because apparently the connection to MySQL was closed (I see lots of SocketException s in the logs). This is probably caused by idling, the server is in development and nobody uses it at night.

I thought Hibernate, JDBC or some other layer below my app would manage the connection and reopen it if neccessary, but apparently not. Is there a configuration parameter I missed?

persistence.xml

http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd" version="2.0">

<persistence-unit name="manager">

<class>example.data.entities.User</class>
<class>example.data.entities.Player</class>

<properties>
    <property name="hibernate.dialect" value="example.data.HibernateDialect" />
    <property name="hibernate.max_fetch_depth" value="3" />
    <property name="hibernate.hbm2ddl.auto" value="update" />

    <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />

</properties>

</persistence-unit>

EntityManagerFactory creation

    log.info("Connecting to database @ " + dbUrl + " using " + dbUser + "/" + dbPass);

    emf = Persistence.createEntityManagerFactory("manager", Maps.create(
            "javax.persistence.jdbc.user", dbUser,
            "javax.persistence.jdbc.password", dbPass,
            "javax.persistence.jdbc.url", dbUrl
    ));

A query

            try
            {

                TypedQuery<User> q = em.createQuery("SELECT u FROM User u WHERE u.email = :mail", User.class);
                q.setParameter("mail", email);
                try {
                    u = q.getSingleResult();
                    log.info("Authenticating: " + u);
                } catch (NoResultException e) {
                    return false;
                }

            } finally {
                em.close();
            }

Answer 1

As you suggest, it is because mysql closes idle connections after each wait_timeout passes; you have some options to work-around your problem:

• use a connection pool manager, like c3p0 or apache DBCP . This will take care of revalidation of connections on request, eventually you can specify which query to run to test if connection is alive.
• set wait_timeout in mysql large enough for your use case (default is 8 hrs).
• setup a scheduled task (for instance using quartz ) that refreshes connections, "pinging" the mysql server.

Answer 2

mysql driver supports autoReconnect the jdbc url will look like jdbc:mysql://localhost/bms_company?autoReconnect=true

if u suspect mysql is dropping connections Try adding the following entries at the end of MySQL's my.ini file. This file is located in the MySQL installation's root folder.

#The number of seconds the mysqld server is waiting for a connect packet before responding with 'Bad handshake' connect_timeout=0

#The number of seconds the server waits for activity on an interactive connection before closing it. interactive_timeout=2000000

#The number of seconds the server waits for activity on a connection before closing it wait_timeout=2000000

--Kiran.Kumar