HTTP Status 500 - exception
javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException: could not load an entity: [net.bmo.model.BmoCalendar#2]
The root cause of this error is:
root cause:java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
Basically this means that the DB connection times out and when the app. went back to the DB to retrieve some data the connection had been lost.
Solution? Add connection pooling. Something I'd been meaning to get round to but hadn't had a chance. So I added C3P0 Connection pooling. I'm using Hibernate so I added the following dependency to the pom.xml:
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-c3p0</artifactId>
<version>3.3.2.GA</version>
</dependency>
This drops in the required jar(s)
hibernate-core-3.3.8.GA.jar and c3p0-0.9.1.jar add them to the class path if you don't already have them.Next I added the c3p0 properties to the persistence.xml file. The amendments are highlighted in blue.
<?xml version="1.0" encoding="UTF-8"?>
<persistence 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" version="1.0">
<persistence-unit name="myPersistence"
transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence
<properties>
<property name = "hibernate.connection.driver_class"
value = "com.mysql.jdbc.Driver"/>
<property name = "hibernate.connection.url"
value = "jdbc:mysql://localhost:3306/myDB"/>
<property name = "hibernate.connection.username" value = "uid"/>
<property name = "hibernate.connection.password" value = "pwd"/>
<property name = "hibernate.hbm2ddl.auto" value = "validate"/>
<property name="hibernate.connection.provider_class"
value="org.hibernate.connection.C3P0ConnectionProvider" />
<property name="hibernate.c3p0.max_size" value="100" />
<property name="hibernate.c3p0.min_size" value="0" />
<property name="hibernate.c3p0.acquire_increment" value="1" />
<property name="hibernate.c3p0.idle_test_period" value="300" />
<property name="hibernate.c3p0.max_statements" value="0" />
<property name="hibernate.c3p0.timeout" value="100" />
</properties>
</persistence-unit>
</persistence>
The effect of the lines above is to force the test of the connections in the pool at regular intervals and refresh the connection if required. This prevented the above error for my deployment. I did this without making any changes in the MySQL Database configuration
