3.12 Using Connector/J with Tomcat

The following instructions are based on the instructions for Tomcat-5.x, available at http://tomcat.apache.org/tomcat-5.5-doc/jndi-datasource-examples-howto.html which is current at the time this document was written.

First, install the .jar file that comes with Connector/J in $CATALINA_HOME/common/lib so that it is available to all applications installed in the container.

Next, configure the JNDI DataSource by adding a declaration resource to $CATALINA_HOME/conf/server.xml in the context that defines your web application:

  <Context ....>
  ...
  <Resource name="jdbc/MySQLDB"
               auth="Container"
               type="javax.sql.DataSource"/>
  <ResourceParams name="jdbc/MySQLDB">
    <parameter>
      <name>factory</name>
      <value>org.apache.commons.dbcp.BasicDataSourceFactory</value>
    </parameter>
    <parameter>
      <name>maxActive</name>
      <value>10</value>
    </parameter>
    <parameter>
      <name>maxIdle</name>
      <value>5</value>
    </parameter>
    <parameter>
      <name>validationQuery</name>
      <value>SELECT 1</value>
    </parameter>
    <parameter>
      <name>testOnBorrow</name>
      <value>true</value>
    </parameter>
    <parameter>
      <name>testWhileIdle</name>
      <value>true</value>
    </parameter>
    <parameter>
      <name>timeBetweenEvictionRunsMillis</name>
      <value>10000</value>
    </parameter>
    <parameter>
      <name>minEvictableIdleTimeMillis</name>
      <value>60000</value>
    </parameter>
    <parameter>
     <name>username</name>
     <value>someuser</value>
    </parameter>
    <parameter>
     <name>password</name>
     <value>somepass</value>
    </parameter>
    <parameter>
       <name>driverClassName</name>
       <value>com.mysql.cj.jdbc.Driver</value>
    </parameter>
    <parameter>
      <name>url</name>
      <value>jdbc:mysql://localhost:3306/test</value>
    </parameter>
  </ResourceParams>
</Context>

Connector/J introduces a facility whereby, rather than use a validationQuery value of SELECT 1, it is possible to use validationQuery with a value set to /* ping */. This sends a ping to the server which then returns a fake result set. This is a lighter weight solution. It also has the advantage that if using ReplicationConnection or LoadBalancedConnection type connections, the ping will be sent across all active connections. The following XML snippet illustrates how to select this option:

<parameter>
 <name>validationQuery</name>
 <value>/* ping */</value>
</parameter>

Note that /* ping */ has to be specified exactly.

In general, follow the installation instructions that come with your version of Tomcat, as the way you configure datasources in Tomcat changes from time to time, and if you use the wrong syntax in your XML file, you will most likely end up with an exception similar to the following:

Error: java.sql.SQLException: Cannot load JDBC driver class 'null ' SQL
state: null

Note that the auto-loading of drivers having the META-INF/service/java.sql.Driver class in JDBC 4.0 and later causes an improper undeployment of the Connector/J driver in Tomcat on Windows. Namely, the Connector/J jar remains locked. This is an initialization problem that is not related to the driver. The possible workarounds, if viable, are as follows: use "antiResourceLocking=true" as a Tomcat Context attribute, or remove the META-INF/ directory.