oracle.toplink.essentials.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Oracle TopLink Essentials - 2.0.1

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
  <persistence-unit name="FrTreePU2" transaction-type="RESOURCE_LOCAL">
    <provider>oracle.toplink.essentials.PersistenceProvider</provider>
    <class>frtree.City</class>
    <class>frtree.Company</class>
    <class>frtree.Contacts</class>
    <class>frtree.Groupcontact</class>
    <class>frtree.Grouptovar</class>
    <properties>
      <property name="toplink.jdbc.user" value="zzzz"/>
      <property name="toplink.jdbc.password" value="zzzz"/>
      <property name="toplink.jdbc.url" value="jdbc:mysql://zzzzzz:3306/zzzzz"/>
      <property name="toplink.jdbc.driver" value="com.mysql.jdbc.Driver"/>
    </properties>
  </persistence-unit>
</persistence>

autoReconnect=true

<property name="toplink.jdbc.url" value="jdbc:mysql://ip:3306/nameDB?autoReconnect=true"/>

ComboPooledDataSource cpds = new ComboPooledDataSource();
cpds.setDriverClass( "com.mysql.jdbc.Driver" );             
cpds.setJdbcUrl( "jdbc:mysql://ip:3306/nameDB" );
cpds.setUser("user");                                  
cpds.setPassword("pass");                                  
	
cpds.setMinPoolSize(5);                                     
cpds.setAcquireIncrement(5);
cpds.setMaxPoolSize(20);

oracle.toplink.essentials.PersistenceProvider

package my.desktop.app;
class SessionCustomizer implements oracle.toplink.essentials.tools.sessionconfiguration.SessionCustomizer

<property name="toplink.session.customizer" value="my.desktop.app.SessionCustomizer" />

DataSource ds = DataSources.unpooledDataSource("myServerURL", "login", "pwd"); 
DataSource pooled = DataSources.pooledDataSource(ds); 
JNDIConnector conn = (JNDIConnector)sn.getLogin().getConnector(); 
conn.setDataSource(pooled); 
conn.setLookupType(JNDIConnector.STRING_LOOKUP); 

log4j:WARN No appenders could be found for logger (com.mchange.v2.log.MLog).
log4j:WARN Please initialize the log4j system properly.
java.lang.ClassCastException: oracle.toplink.essentials.sessions.DefaultConnector cannot be cast to oracle.toplink.essentials.jndi.JNDIConnector

JNDIConnector conn = (JNDIConnector)sn.getLogin().getConnector(); 

public void customize(Session sn) {
       
System.setProperty("com.mchange.v2.log.MLog", "com.mchange.v2.log.FallbackMLog");
System.setProperty("com.mchange.v2.log.FallbackMLog.DEFAULT_CUTOFF_LEVEL", "WARNING");