tomcat-uidm/webapps/docs/jndi-datasource-examples-howto.html - UniIdentify/tomcat - Gitiles

 <html><head><META http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Apache Tomcat 6.0 (6.0.39) - JNDI Datasource HOW-TO</title><meta name="author" content="Les Hughes"><meta name="author" content="David Haraburda"><meta name="author" content="Glenn Nielsen"><meta name="author" content="Yoav Shapira"><style type="text/css" media="print">
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 <ul><li><a href="#Introduction">Introduction</a></li><li><a href="#DriverManager,_the_service_provider_mechanism_and_memory_leaks">DriverManager, the service provider mechanism and memory leaks</a></li><li><a href="#Database_Connection_Pool_(DBCP)_Configurations">Database Connection Pool (DBCP) Configurations</a><ol><li><a href="#Installation">Installation</a></li><li><a href="#Preventing_database_connection_pool_leaks">Preventing database connection pool leaks</a></li><li><a href="#MySQL_DBCP_Example">MySQL DBCP Example</a></li><li><a href="#Oracle_8i,_9i_&_10g">Oracle 8i, 9i &amp; 10g</a></li><li><a href="#PostgreSQL">PostgreSQL</a></li></ol></li><li><a href="#Non-DBCP_Solutions">Non-DBCP Solutions</a></li><li><a href="#Oracle_8i_with_OCI_client">Oracle 8i with OCI client</a><ol><li><a href="#Oracle_8i_with_OCI_client/Introduction">Introduction</a></li><li><a href="#Putting_it_all_together">Putting it all together</a></li></ol></li><li><a href="#Common_Problems">Common Problems</a><ol><li><a href="#Intermittent_Database_Connection_Failures">Intermittent Database Connection Failures</a></li><li><a href="#Random_Connection_Closed_Exceptions">Random Connection Closed Exceptions</a></li><li><a href="#Context_versus_GlobalNamingResources">Context versus GlobalNamingResources</a></li><li><a href="#JNDI_Resource_Naming_and_Realm_Interaction">JNDI Resource Naming and Realm Interaction</a></li></ol></li></ul>
 </blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Introduction"><strong>Introduction</strong></a></font></td></tr><tr><td><blockquote>

 <p>JNDI Datasource configuration is covered extensively in the
 JNDI-Resources-HOWTO.  However, feedback from <code>tomcat-user</code> has
 shown that specifics for individual configurations can be rather tricky.</p>

 <p>Here then are some example configurations that have been posted to
 tomcat-user for popular databases and some general tips for db usage.</p>

 <p>You should be aware that since these notes are derived from configuration
 and/or feedback posted to <code>tomcat-user</code> YMMV :-). Please let us
 know if you have any other tested configurations that you feel may be of use
 to the wider audience, or if you feel we can improve this section in anyway.</p>

 <p>
 <b>Please note that JNDI resource configuration changed somewhat between
 Tomcat 5.0.x and Tomcat 5.5.x.</b>  You will most likely need to modify older
 JNDI resource configurations to match the syntax in the example below in order
 to make them work in Tomcat 6.x.x.
 </p>

 <p>
 Also, please note that JNDI DataSource configuration in general, and this
 tutorial in particular, assumes that you have read and understood the
 <a href="config/context.html">Context</a> and
 <a href="config/host.html">Host</a> configuration references, including
 the section about Automatic Application Deployment in the latter reference.
 </p>
 </blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="DriverManager, the service provider mechanism and memory leaks"><!--()--></a><a name="DriverManager,_the_service_provider_mechanism_and_memory_leaks"><strong>DriverManager, the service provider mechanism and memory leaks</strong></a></font></td></tr><tr><td><blockquote>

 <p><code>java.sql.DriverManager</code> supports the
 <a href="http://docs.oracle.com/javase/6/docs/api/index.html?java/sql/DriverManager.html">service
 provider</a> mechanism. This feature is that all the available JDBC drivers
 that announce themselves by providing a <code>META-INF/services/java.sql.Driver</code>
 file are automatically discovered, loaded and registered,
 relieving you from the need to load the database driver explicitly before
 you create a JDBC connection.
 However, the implementation is fundamentally broken in all Java versions for
 a servlet container environment. The problem is that
 <code>java.sql.DriverManager</code> will scan for the drivers only once.</p>

 <p>The <a href="config/listeners.html">JRE Memory Leak Prevention Listener</a>
 that is included with Apache Tomcat solves this by triggering the drivers scan
 during Tomcat startup. This is enabled by default. It means that only
 libraries visible to the listener such as the ones in
 <code>$CATALINA_BASE/lib</code> will be scanned for database drivers.
 If you are considering disabling this feature, note that
 the scan would be triggered by the first web application that is
 using JDBC, leading to failures when this web application is reloaded
 and for other web applications that rely on this feature.
 </p>

 <p>Thus, the web applications that have database drivers in their
 <code>WEB-INF/lib</code> directory cannot rely on the service provider
 mechanism and should register the drivers explicitly.</p>

 <p>The list of drivers in <code>java.sql.DriverManager</code> is also
 a known source of memory leaks. Any Drivers registered
 by a web application must be deregistered when the web application stops.
 Tomcat will attempt to automatically discover and deregister any
 JDBC drivers loaded by the web application class loader when the web
 application stops.
 However, it is expected that applications do this for themselves via
 a <code>ServletContextListener</code>.
 </p>

 </blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Database Connection Pool (DBCP) Configurations"><!--()--></a><a name="Database_Connection_Pool_(DBCP)_Configurations"><strong>Database Connection Pool (DBCP) Configurations</strong></a></font></td></tr><tr><td><blockquote>

 <p>The default database connection pool implementation in Apache Tomcat
 relies on the libraries from the
 <a href="http://commons.apache.org/">Apache Commons</a> project.
 The following libraries are used:
 </p>

 <ul>
 <li>Commons DBCP</li>
 <li>Commons Pool</li>
 </ul>

 <p>
 These libraries are located in a single JAR at
 <code>$CATALINA_HOME/lib/tomcat-dbcp.jar</code>. However,
 only the classes needed for connection pooling have been included, and the
 packages have been renamed to avoid interfering with applications.
 </p>

 <p>DBCP 1.3 provides support for JDBC 3.0.</p>

 <table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Installation"><strong>Installation</strong></a></font></td></tr><tr><td><blockquote>

 <p>See the <a href="http://commons.apache.org/dbcp/configuration.html">
 DBCP documentation</a> for a complete list of configuration parameters.
 </p>

 </blockquote></td></tr></table>

 <table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Preventing database connection pool leaks"><!--()--></a><a name="Preventing_database_connection_pool_leaks"><strong>Preventing database connection pool leaks</strong></a></font></td></tr><tr><td><blockquote>

 <p>
 A database connection pool creates and manages a pool of connections
 to a database. Recycling and reusing already existing connections
 to a database is more efficient than opening a new connection.
 </p>

 <p>
 There is one problem with connection pooling.  A web application has
 to explicitly close ResultSet's, Statement's, and Connection's.
 Failure of a web application to close these resources can result in
 them never being available again for reuse, a database connection pool "leak".
 This can eventually result in your web application database connections failing
 if there are no more available connections.</p>

 <p>
 There is a solution to this problem.  The Apache Commons DBCP can be
 configured to track and recover these abandoned database connections.  Not
 only can it recover them, but also generate a stack trace for the code
 which opened these resources and never closed them.</p>

 <p>
 To configure a DBCP DataSource so that abandoned database connections are
 removed and recycled add the following attribute to the
 <code>Resource</code> configuration for your DBCP DataSource:
 </p>

 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>removeAbandoned="true"</pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>

 <p>
 When available database connections run low DBCP will recover and recycle
 any abandoned database connections it finds. The default is <code>false</code>.
 </p>

 <p>
 Use the <code>removeAbandonedTimeout</code> attribute to set the number
 of seconds a database connection has been idle before it is considered abandoned.
 </p>

 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>removeAbandonedTimeout="60"</pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>

 <p>
 The default timeout for removing abandoned connections is 300 seconds.
 </p>

 <p>
 The <code>logAbandoned</code> attribute can be set to <code>true</code>
 if you want DBCP to log a stack trace of the code which abandoned the
 database connection resources.
 </p>
 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>logAbandoned="true"</pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>
 <p>
 The default is <code>false</code>.
 </p>

 </blockquote></td></tr></table>

 <table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="MySQL DBCP Example"><!--()--></a><a name="MySQL_DBCP_Example"><strong>MySQL DBCP Example</strong></a></font></td></tr><tr><td><blockquote>

 <h3>0. Introduction</h3>
 <p>Versions of <a href="http://www.mysql.com/products/mysql/index.html">MySQL</a> and JDBC
 drivers that have been reported to work:
 </p>
 <ul>
 <li>MySQL 3.23.47, MySQL 3.23.47 using InnoDB,, MySQL 3.23.58,  MySQL 4.0.1alpha</li>
 <li><a href="http://www.mysql.com/products/connector-j">Connector/J</a> 3.0.11-stable (the official JDBC Driver)</li>
 <li><a href="http://mmmysql.sourceforge.net">mm.mysql</a> 2.0.14 (an old 3rd party JDBC Driver)</li>
 </ul>

 <p>Before you proceed, don't forget to copy the JDBC Driver's jar into <code>$CATALINA_HOME/lib</code>.</p>

 <h3>1. MySQL configuration</h3>
 <p>
 Ensure that you follow these instructions as variations can cause problems.
 </p>

 <p>Create a new test user, a new database and a single test table.
 Your MySQL user <strong>must</strong> have a password assigned. The driver
 will fail if you try to connect with an empty password.
 </p>
 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 mysql&gt; GRANT ALL PRIVILEGES ON *.* TO javauser@localhost
     -&gt;   IDENTIFIED BY 'javadude' WITH GRANT OPTION;
 mysql&gt; create database javatest;
 mysql&gt; use javatest;
 mysql&gt; create table testdata (
     -&gt;   id int not null auto_increment primary key,
     -&gt;   foo varchar(25),
     -&gt;   bar int);
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>
 <blockquote>
 <strong>Note:</strong> the above user should be removed once testing is
 complete!
 </blockquote>

 <p>Next insert some test data into the testdata table.
 </p>
 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 mysql&gt; insert into testdata values(null, 'hello', 12345);
 Query OK, 1 row affected (0.00 sec)

 mysql&gt; select * from testdata;
 +----+-------+-------+
 | ID | FOO   | BAR   |
 +----+-------+-------+
 |  1 | hello | 12345 |
 +----+-------+-------+
 1 row in set (0.00 sec)

 mysql&gt;
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>

 <h3>2. Context configuration</h3>
 <p>Configure the JNDI DataSource in Tomcat by adding a declaration for your
 resource to your <a href="config/context.html">Context</a>.</p>
 <p>For example:</p>
 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 &lt;Context&gt;

     &lt;!-- maxActive: Maximum number of database connections in pool. Make sure you
          configure your mysqld max_connections large enough to handle
          all of your db connections. Set to -1 for no limit.
          --&gt;

     &lt;!-- maxIdle: Maximum number of idle database connections to retain in pool.
          Set to -1 for no limit.  See also the DBCP documentation on this
          and the minEvictableIdleTimeMillis configuration parameter.
          --&gt;

     &lt;!-- maxWait: Maximum time to wait for a database connection to become available
          in ms, in this example 10 seconds. An Exception is thrown if
          this timeout is exceeded.  Set to -1 to wait indefinitely.
          --&gt;

     &lt;!-- username and password: MySQL username and password for database connections  --&gt;

     &lt;!-- driverClassName: Class name for the old mm.mysql JDBC driver is
          org.gjt.mm.mysql.Driver - we recommend using Connector/J though.
          Class name for the official MySQL Connector/J driver is com.mysql.jdbc.Driver.
          --&gt;

     &lt;!-- url: The JDBC connection url for connecting to your MySQL database.
          --&gt;

   &lt;Resource name="jdbc/TestDB" auth="Container" type="javax.sql.DataSource"
                maxActive="100" maxIdle="30" maxWait="10000"
                username="javauser" password="javadude" driverClassName="com.mysql.jdbc.Driver"
                url="jdbc:mysql://localhost:3306/javatest"/&gt;

 &lt;/Context&gt;
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>

 <h3>3. web.xml configuration</h3>

 <p>Now create a <code>WEB-INF/web.xml</code> for this test application.</p>
 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 &lt;web-app xmlns="http://java.sun.com/xml/ns/j2ee"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
 http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
     version="2.4"&gt;
   &lt;description&gt;MySQL Test App&lt;/description&gt;
   &lt;resource-ref&gt;
       &lt;description&gt;DB Connection&lt;/description&gt;
       &lt;res-ref-name&gt;jdbc/TestDB&lt;/res-ref-name&gt;
       &lt;res-type&gt;javax.sql.DataSource&lt;/res-type&gt;
       &lt;res-auth&gt;Container&lt;/res-auth&gt;
   &lt;/resource-ref&gt;
 &lt;/web-app&gt;
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>

 <h3>4. Test code</h3>
 <p>Now create a simple <code>test.jsp</code> page for use later.
 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 &lt;%@ taglib uri="http://java.sun.com/jsp/jstl/sql" prefix="sql" %&gt;
 &lt;%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %&gt;

 &lt;sql:query var="rs" dataSource="jdbc/TestDB"&gt;
 select id, foo, bar from testdata
 &lt;/sql:query&gt;

 &lt;html&gt;
   &lt;head&gt;
     &lt;title&gt;DB Test&lt;/title&gt;
   &lt;/head&gt;
   &lt;body&gt;

   &lt;h2&gt;Results&lt;/h2&gt;

 &lt;c:forEach var="row" items="${rs.rows}"&gt;
     Foo ${row.foo}&lt;br/&gt;
     Bar ${row.bar}&lt;br/&gt;
 &lt;/c:forEach&gt;

   &lt;/body&gt;
 &lt;/html&gt;
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>
 </p>

 <p>That JSP page makes use of <a href="http://java.sun.com/products/jsp/jstl">JSTL</a>'s
 SQL and Core taglibs. You can get it from
 <a href="http://tomcat.apache.org/taglibs/standard/">Apache Tomcat Taglibs - Standard Tag Library</a>
 project &mdash; just make sure you get a 1.1.x release. Once you have JSTL,
 copy <code>jstl.jar</code> and <code>standard.jar</code> to your web app's
 <code>WEB-INF/lib</code> directory.

 </p>

 <p>Finally deploy your web app into <code>$CATALINA_BASE/webapps</code> either
 as a warfile called <code>DBTest.war</code> or into a sub-directory called
 <code>DBTest</code></p>
 <p>Once deployed, point a browser at
 <code>http://localhost:8080/DBTest/test.jsp</code> to view the fruits of
 your hard work.</p>

 </blockquote></td></tr></table>

 <table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Oracle 8i, 9i & 10g"><!--()--></a><a name="Oracle_8i,_9i_&_10g"><strong>Oracle 8i, 9i &amp; 10g</strong></a></font></td></tr><tr><td><blockquote>
 <h3>0.    Introduction</h3>

 <p>Oracle requires minimal changes from the MySQL configuration except for the
 usual gotchas :-)</p>
 <p>Drivers for older Oracle versions may be distributed as *.zip files rather
 than *.jar files. Tomcat will only use <code>*.jar</code> files installed in
 <code>$CATALINA_HOME/lib</code>. Therefore <code>classes111.zip</code>
 or <code>classes12.zip</code> will need to be renamed with a <code>.jar</code>
 extension. Since jarfiles are zipfiles, there is no need to unzip and jar these
 files - a simple rename will suffice.</p>

 <p>For Oracle 9i onwards you should use <code>oracle.jdbc.OracleDriver</code>
 rather than <code>oracle.jdbc.driver.OracleDriver</code> as Oracle have stated
 that <code>oracle.jdbc.driver.OracleDriver</code> is deprecated and support
 for this driver class will be discontinued in the next major release.
 </p>

 <h3>1. Context configuration</h3>
 <p>In a similar manner to the mysql config above, you will need to define your
 Datasource in your <a href="config/context.html">Context</a>. Here we define a
 Datasource called myoracle using the thin driver to connect as user scott,
 password tiger to the sid called mysid. (Note: with the thin driver this sid is
 not the same as the tnsname). The schema used will be the default schema for the
 user scott.</p>

 <p>Use of the OCI driver should simply involve a changing thin to oci in the URL string.
 </p>
 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 &lt;Resource name="jdbc/myoracle" auth="Container"
               type="javax.sql.DataSource" driverClassName="oracle.jdbc.OracleDriver"
               url="jdbc:oracle:thin:@127.0.0.1:1521:mysid"
               username="scott" password="tiger" maxActive="20" maxIdle="10"
               maxWait="-1"/&gt;
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>

 <h3>2.    web.xml configuration</h3>
 <p>You should ensure that you respect the element ordering defined by the DTD when you
 create you applications web.xml file.</p>
 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 &lt;resource-ref&gt;
  &lt;description&gt;Oracle Datasource example&lt;/description&gt;
  &lt;res-ref-name&gt;jdbc/myoracle&lt;/res-ref-name&gt;
  &lt;res-type&gt;javax.sql.DataSource&lt;/res-type&gt;
  &lt;res-auth&gt;Container&lt;/res-auth&gt;
 &lt;/resource-ref&gt;
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>
 <h3>3.   Code example</h3>
 <p>You can use the same example application as above (asuming you create the required DB
 instance, tables etc.) replacing the Datasource code with something like</p>
 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 Context initContext = new InitialContext();
 Context envContext  = (Context)initContext.lookup("java:/comp/env");
 DataSource ds = (DataSource)envContext.lookup("jdbc/myoracle");
 Connection conn = ds.getConnection();
 //etc.
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>
 </blockquote></td></tr></table>


 <table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="PostgreSQL"><strong>PostgreSQL</strong></a></font></td></tr><tr><td><blockquote>
 <h3>0.    Introduction</h3>
 <p>PostgreSQL is configured in a similar manner to Oracle.</p>

 <h3>1. Required files </h3>
 <p>
 Copy the Postgres JDBC jar to $CATALINA_HOME/lib. As with Oracle, the
 jars need to be in this directory in order for DBCP's Classloader to find
 them. This has to be done regardless of which configuration step you take next.
 </p>

 <h3>2. Resource configuration</h3>

 <p>
 You have two choices here: define a datasource that is shared across all Tomcat
 applications, or define a datasource specifically for one application.
 </p>

 <h4>2a. Shared resource configuration</h4>
 <p>
 Use this option if you wish to define a datasource that is shared across
 multiple Tomcat applications, or if you just prefer defining your datasource
 in this file.
 </p>
 <p><i>This author has not had success here, although others have reported so.
 Clarification would be appreciated here.</i></p>

 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 &lt;Resource name="jdbc/postgres" auth="Container"
           type="javax.sql.DataSource" driverClassName="org.postgresql.Driver"
           url="jdbc:postgresql://127.0.0.1:5432/mydb"
           username="myuser" password="mypasswd" maxActive="20" maxIdle="10" maxWait="-1"/&gt;
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>
 <h4>2b. Application-specific resource configuration</h4>

 <p>
 Use this option if you wish to define a datasource specific to your application,
 not visible to other Tomcat applications. This method is less invasive to your
 Tomcat installation.
 </p>

 <p>
 Create a resource definition for your <a href="config/context.html">Context</a>.
 The Context element should look something like the following.
 </p>

 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 &lt;Context&gt;

 &lt;Resource name="jdbc/postgres" auth="Container"
           type="javax.sql.DataSource" driverClassName="org.postgresql.Driver"
           url="jdbc:postgresql://127.0.0.1:5432/mydb"
           username="myuser" password="mypasswd" maxActive="20" maxIdle="10"
 maxWait="-1"/&gt;
 &lt;/Context&gt;
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>

 <h3>3. web.xml configuration</h3>
 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 &lt;resource-ref&gt;
  &lt;description&gt;postgreSQL Datasource example&lt;/description&gt;
  &lt;res-ref-name&gt;jdbc/postgres&lt;/res-ref-name&gt;
  &lt;res-type&gt;javax.sql.DataSource&lt;/res-type&gt;
  &lt;res-auth&gt;Container&lt;/res-auth&gt;
 &lt;/resource-ref&gt;
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>

 <h4>4. Accessing the datasource</h4>
 <p>
 When accessing the datasource programmatically, remember to prepend
 <code>java:/comp/env</code> to your JNDI lookup, as in the following snippet of
 code. Note also that "jdbc/postgres" can be replaced with any value you prefer, provided
 you change it in the above resource definition file as well.
 </p>

 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 InitialContext cxt = new InitialContext();
 if ( cxt == null ) {
    throw new Exception("Uh oh -- no context!");
 }

 DataSource ds = (DataSource) cxt.lookup( "java:/comp/env/jdbc/postgres" );

 if ( ds == null ) {
    throw new Exception("Data source not found!");
 }
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>

 </blockquote></td></tr></table>
 </blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Non-DBCP Solutions"><!--()--></a><a name="Non-DBCP_Solutions"><strong>Non-DBCP Solutions</strong></a></font></td></tr><tr><td><blockquote>
 <p>
 These solutions either utilise a single connection to the database (not recommended for anything other
 than testing!) or some other pooling technology.
 </p>
 </blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Oracle 8i with OCI client"><!--()--></a><a name="Oracle_8i_with_OCI_client"><strong>Oracle 8i with OCI client</strong></a></font></td></tr><tr><td><blockquote>
 <table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Oracle 8i with OCI client/Introduction"><!--()--></a><a name="Oracle_8i_with_OCI_client/Introduction"><strong>Introduction</strong></a></font></td></tr><tr><td><blockquote>
 <p>Whilst not strictly addressing the creation of a JNDI DataSource using the OCI client, these notes can be combined with the
 Oracle and DBCP solution above.</p>
 <p>
 In order to use OCI driver, you should have an Oracle client installed. You should have installed
 Oracle8i(8.1.7) client from cd,  and download the suitable JDBC/OCI
 driver(Oracle8i 8.1.7.1 JDBC/OCI Driver) from <a href="http://otn.oracle.com/">otn.oracle.com</a>.
 </p>
 <p>
 After renaming <code>classes12.zip</code> file to <code>classes12.jar</code>
 for Tomcat, copy it into <code>$CATALINA_HOME/lib</code>.
 You may also have to remove the <code>javax.sql.*</code> classes
 from this file depending upon the version of Tomcat and JDK you are using.
 </p>
 </blockquote></td></tr></table>

 <table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Putting it all together"><!--()--></a><a name="Putting_it_all_together"><strong>Putting it all together</strong></a></font></td></tr><tr><td><blockquote>
 <p>
 Ensure that you have the <code>ocijdbc8.dll</code> or <code>.so</code> in your <code>$PATH</code> or <code>LD_LIBRARY_PATH</code>
  (possibly in <code>$ORAHOME\bin</code>) and also confirm that the native library can be loaded by a simple test program
 using <code>System.loadLibrary("ocijdbc8");</code>
 </p>
 <p>
 You should next create a simple test servlet or jsp that has these
 <strong>critical lines</strong>:
 </p>
 <div align="left"><table cellspacing="4" cellpadding="0" border="0"><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#ffffff" height="1"><pre>
 DriverManager.registerDriver(new
 oracle.jdbc.driver.OracleDriver());
 conn =
 DriverManager.getConnection("jdbc:oracle:oci8:@database","username","password");
 </pre></td><td bgcolor="#023264" width="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr><tr><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td><td bgcolor="#023264" width="1" height="1"><img src="./images/void.gif" alt="" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table></div>
 <p>
 where database is of the form <code>host:port:SID</code> Now if you try to access the URL of your
 test servlet/jsp and what you get is a
 <code>ServletException</code> with a root cause of <code>java.lang.UnsatisfiedLinkError:get_env_handle</code>.
 </p>
 <p>
 First, the <code>UnsatisfiedLinkError</code> indicates that you have
 <ul>
 <li>a mismatch between your JDBC classes file and
 your Oracle client version. The giveaway here is the message stating that a needed library file cannot be
 found. For example, you may be using a classes12.zip file from Oracle Version 8.1.6 with a Version 8.1.5
 Oracle client. The classeXXXs.zip file and Oracle client software versions must match.
 </li>
 <li>A <code>$PATH</code>, <code>LD_LIBRARY_PATH</code> problem.</li>
 <li>It has been reported that ignoring the driver you have downloded from otn and using
 the classes12.zip file from the directory <code>$ORAHOME\jdbc\lib</code> will also work.
 </li>
 </ul>
 </p>
 <p>
 Next you may experience the error <code>ORA-06401 NETCMN: invalid driver designator</code>
 </p>
 <p>
 The Oracle documentation says : "Cause: The login (connect) string contains an invalid
 driver designator. Action: Correct the string and re-submit."

 Change the database connect string (of the form <code>host:port:SID</code>) with this one:
 <code>(description=(address=(host=myhost)(protocol=tcp)(port=1521))(connect_data=(sid=orcl)))</code>
 </p>
 <p>
 <i>Ed. Hmm, I don't think this is really needed if you sort out your TNSNames - but I'm not an Oracle DBA :-)</i>
 </p>
 </blockquote></td></tr></table>
 </blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Common Problems"><!--()--></a><a name="Common_Problems"><strong>Common Problems</strong></a></font></td></tr><tr><td><blockquote>
 <p>Here are some common problems encountered with a web application which
 uses a database and tips for how to solve them.</p>

 <table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Intermittent Database Connection Failures"><!--()--></a><a name="Intermittent_Database_Connection_Failures"><strong>Intermittent Database Connection Failures</strong></a></font></td></tr><tr><td><blockquote>
 <p>
 Tomcat runs within a JVM.  The JVM periodically performs garbage collection
 (GC) to remove java objects which are no longer being used.  When the JVM
 performs GC execution of code within Tomcat freezes. If the maximum time
 configured for establishment of a database connection is less than the amount
 of time garbage collection took you can get a database connection failure.
 </p>

 <p>To collect data on how long garbage collection is taking add the
 <code>-verbose:gc</code> argument to your <code>CATALINA_OPTS</code>
 environment variable when starting Tomcat.  When verbose gc is enabled
 your <code>$CATALINA_BASE/logs/catalina.out</code> log file will include
 data for every garbage collection including how long it took.</p>

 <p>When your JVM is tuned correctly 99% of the time a GC will take less
 than one second.  The remainder will only take a few seconds.  Rarely,
 if ever should a GC take more than 10 seconds.</p>

 <p>Make sure that the db connection timeout is set to 10-15 seconds.
 For the DBCP you set this using the parameter <code>maxWait</code>.</p>

 </blockquote></td></tr></table>

 <table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Random Connection Closed Exceptions"><!--()--></a><a name="Random_Connection_Closed_Exceptions"><strong>Random Connection Closed Exceptions</strong></a></font></td></tr><tr><td><blockquote>
 <p>
 These can occur when one request gets a db connection from the connection
 pool and closes it twice.  When using a connection pool, closing the
 connection just returns it to the pool for reuse by another request,
 it doesn't close the connection.  And Tomcat uses multiple threads to
 handle concurrent requests. Here is an example of the sequence
 of events which could cause this error in Tomcat:
 </p>
 <pre>
   Request 1 running in Thread 1 gets a db connection.

   Request 1 closes the db connection.

   The JVM switches the running thread to Thread 2

   Request 2 running in Thread 2 gets a db connection
   (the same db connection just closed by Request 1).

   The JVM switches the running thread back to Thread 1

   Request 1 closes the db connection a second time in a finally block.

   The JVM switches the running thread back to Thread 2

   Request 2 Thread 2 tries to use the db connection but fails
   because Request 1 closed it.
 </pre>
 <p>
 Here is an example of properly written code to use a database connection
 obtained from a connection pool:
 </p>
 <pre>
   Connection conn = null;
   Statement stmt = null;  // Or PreparedStatement if needed
   ResultSet rs = null;
   try {
     conn = ... get connection from connection pool ...
     stmt = conn.createStatement("select ...");
     rs = stmt.executeQuery();
     ... iterate through the result set ...
     rs.close();
     rs = null;
     stmt.close();
     stmt = null;
     conn.close(); // Return to connection pool
     conn = null;  // Make sure we don't close it twice
   } catch (SQLException e) {
     ... deal with errors ...
   } finally {
     // Always make sure result sets and statements are closed,
     // and the connection is returned to the pool
     if (rs != null) {
       try { rs.close(); } catch (SQLException e) { ; }
       rs = null;
     }
     if (stmt != null) {
       try { stmt.close(); } catch (SQLException e) { ; }
       stmt = null;
     }
     if (conn != null) {
       try { conn.close(); } catch (SQLException e) { ; }
       conn = null;
     }
   }
 </pre>

 </blockquote></td></tr></table>

 <table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Context versus GlobalNamingResources"><!--()--></a><a name="Context_versus_GlobalNamingResources"><strong>Context versus GlobalNamingResources</strong></a></font></td></tr><tr><td><blockquote>
 <p>
   Please note that although the above instructions place the JNDI declarations in a Context
   element, it is possible and sometimes desirable to place these declarations in the
   <a href="config/globalresources.html">GlobalNamingResources</a> section of the server
   configuration file.  A resource placed in the GlobalNamingResources section will be shared
   among the Contexts of the server.
 </p>
 </blockquote></td></tr></table>

 <table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="JNDI Resource Naming and Realm Interaction"><!--()--></a><a name="JNDI_Resource_Naming_and_Realm_Interaction"><strong>JNDI Resource Naming and Realm Interaction</strong></a></font></td></tr><tr><td><blockquote>
 <p>
   In order to get Realms to work, the realm must refer to the datasource as
   defined in the &lt;GlobalNamingResources&gt; or &lt;Context&gt; section, not a datasource as renamed
   using &lt;ResourceLink&gt;.
 </p>
 </blockquote></td></tr></table>

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