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Tomcat example source code file (jndi-datasource-examples-howto.xml)
This example Tomcat source code file (jndi-datasource-examples-howto.xml) is included in the DevDaily.com
"Java Source Code
Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.
The Tomcat jndi-datasource-examples-howto.xml source code
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<!DOCTYPE document [
<!ENTITY project SYSTEM "project.xml">
]>
<document url="jndi-datasource-examples-howto.html">
&project;
<properties>
<author email="leslie.hughes@rubus.com">Les Hughes
<author email="david-tomcat@haraburda.com">David Haraburda
<author>Glenn Nielsen
<author email="yoavs@apache.org">Yoav Shapira
<title>JNDI Datasource HOW-TO
</properties>
<body>
<section name="Table of Contents">
<p>
<a href="#Introduction">Introduction
<a href="#Database Connection Pool (DBCP) Configurations">
Database Connection Pool (DBCP) Configurations</a>
<a href="#Non DBCP Solutions">Non DBCP Solutions
<a href="#Oracle 8i with OCI client">Oracle 8i with OCI client
<a href="#Common Problems">Common Problems
</p>
</section>
<section name="Introduction">
<p>JNDI Datasource configuration is covered extensively in the
JNDI-Resources-HOWTO. However, feedback from <code>tomcat-user 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 useage.</p>
<p>You should be aware that since these notes are derived from configuration
and/or feedback posted to <code>tomcat-user 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 and
<a href="config/host.html">Host configuration references, including
the section about Automatic Application Deployment in the latter reference.
</p>
</section>
<section name="Database Connection Pool (DBCP) Configurations">
<p>DBCP provides support for JDBC 2.0. On systems using a 1.4 JVM DBCP
will support JDBC 3.0. Please let us know if you have used DBCP and its
JDBC 3.0 features with a 1.4 JVM.
</p>
<p>See the
DBCP documentation</a> for a complete list of configuration parameters.
</p>
<subsection name="Installation">
<p>DBCP uses the Jakarta-Commons Database Connection Pool. It relies on
number of Jakarta-Commons components:
<ul>
<li>Jakarta-Commons DBCP
<li>Jakarta-Commons Collections
<li>Jakarta-Commons Pool
</ul>
These libraries are located in a single JAR at
<code>$CATALINA_HOME/lib/tomcat-dbcp.jar. However,
only the classes needed for connection pooling have been included, and the
packages have been renamed to avoid interfering with applications.
</p>
</subsection>
<subsection name="Preventing dB connection pool leaks">
<p>
A database connection pool creates and manages a pool of connections
to a database. Recycling and reusing already existing connections
to a dB is more efficient than opening a new connection.
</p>
<p>
There is one problem with connection pooling. A web application has
to explicetely 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 db connection pool "leak".
This can eventually result in your web application db connections failing
if there are no more available connections.</p>
<p>
There is a solution to this problem. The Jakarta-Commons DBCP can be
configured to track and recover these abandoned dB 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 dB connections are
removed and recycled add the following attribute to the
<code>Resource configuration for your DBCP DataSource:
<source>
removeAbandoned="true"
</source>
When available db connections run low DBCP will recover and recyle
any abandoned dB connections it finds. The default is <code>false.
</p>
<p>
Use the <code>removeAbandonedTimeout attribute to set the number
of seconds a dB connection has been idle before it is considered abandoned.
<source>
removeAbandonedTimeout="60"
</source>
The default timeout for removing abandoned connections is 300 seconds.
</p>
<p>
The <code>logAbandoned attribute can be set to true
if you want DBCP to log a stack trace of the code which abandoned the
dB connection resources.
<source>
logAbandoned="true"
</source>
The default is <code>false.
</p>
</subsection>
<subsection name="MySQL DBCP Example">
<h3>0. Introduction
<p>Versions of MySQL and JDBC drivers that have been reported to work:
<ul>
<li>MySQL 3.23.47, MySQL 3.23.47 using InnoDB,, MySQL 3.23.58, MySQL 4.0.1alpha
<li>Connector/J 3.0.11-stable (the official JDBC Driver)
<li>mm.mysql 2.0.14 (an old 3rd party JDBC Driver)
</ul>
</p>
<p>Before you proceed, don't forget to copy the JDBC Driver's jar into $CATALINA_HOME/lib.
<h3>1. MySQL configuration
<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 have a password assigned. The driver
will fail if you try to connect with an empty password.
<source>
mysql> GRANT ALL PRIVILEGES ON *.* TO javauser@localhost
-> IDENTIFIED BY 'javadude' WITH GRANT OPTION;
mysql> create database javatest;
mysql> use javatest;
mysql> create table testdata (
-> id int not null auto_increment primary key,
-> foo varchar(25),
-> bar int);
</source>
<blockquote>
<strong>Note: the above user should be removed once testing is
complete!
</blockquote>
</p>
<p>Next insert some test data into the testdata table.
<source>
mysql> insert into testdata values(null, 'hello', 12345);
Query OK, 1 row affected (0.00 sec)
mysql> select * from testdata;
+----+-------+-------+
| ID | FOO | BAR |
+----+-------+-------+
| 1 | hello | 12345 |
+----+-------+-------+
1 row in set (0.00 sec)
mysql>
</source>
</p>
<h3>2. Context configuration
<p>Configure the JNDI DataSource in Tomcat by adding a declaration for your
resource to your <a href="config/context.html">Context.
<p>For example:
<source>
<Context path="/DBTest" docBase="DBTest"
debug="5" reloadable="true" crossContext="true">
<!-- maxActive: Maximum number of dB connections in pool. Make sure you
configure your mysqld max_connections large enough to handle
all of your db connections. Set to 0 for no limit.
-->
<!-- maxIdle: Maximum number of idle dB connections to retain in pool.
Set to -1 for no limit. See also the DBCP documentation on this
and the minEvictableIdleTimeMillis configuration parameter.
-->
<!-- maxWait: Maximum time to wait for a dB 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.
-->
<!-- username and password: MySQL dB username and password for dB connections -->
<!-- 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.
-->
<!-- url: The JDBC connection url for connecting to your MySQL dB.
The autoReconnect=true argument to the url makes sure that the
mm.mysql JDBC Driver will automatically reconnect if mysqld closed the
connection. mysqld by default closes idle connections after 8 hours.
-->
<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?autoReconnect=true"/>
</Context>
</source>
</p>
<h3>3. web.xml configuration
<p>Now create a WEB-INF/web.xml for this test application.
<source>
<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">
<description>MySQL Test App</description>
<resource-ref>
<description>DB Connection</description>
<res-ref-name>jdbc/TestDB</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
</resource-ref>
</web-app>
</source>
</p>
<h3>4. Test code
<p>Now create a simple test.jsp page for use later.
<source>
<%@ taglib uri="http://java.sun.com/jsp/jstl/sql" prefix="sql" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<sql:query var="rs" dataSource="jdbc/TestDB">
select id, foo, bar from testdata
</sql:query>
<html>
<head>
<title>DB Test</title>
</head>
<body>
<h2>Results</h2>
<c:forEach var="row" items="${rs.rows}">
Foo ${row.foo}<br/>
Bar ${row.bar}<br/>
</c:forEach>
</body>
</html>
</source>
</p>
<p>That JSP page makes use of JSTL's SQL and Core taglibs. You can get it from Sun's Java Web Services Developer Pack or Jakarta Taglib Standard 1.1 project - just make sure you get a 1.1.x release. Once you have JSTL, copy jstl.jar and standard.jar to your web app's WEB-INF/lib directory.
</p>
<p>Finally deploy your web app into $CATALINA_HOME/webapps either
as a warfile called <code>DBTest.war or into a sub-directory called
<code>DBTest
<p>Once deployed, point a browser at
<code>http://localhost:8080/DBTest/test.jsp to view the fruits of
your hard work.</p>
</subsection>
<subsection name="Oracle 8i, 9i & 10g">
<h3>0. Introduction
<p>Oracle requires minimal changes from the MySQL configuration except for the
usual gotchas :-)</p>
<p>Drivers for older Oracle versions may be distributed as *.zip files rather
than *.jar files. Tomcat will only use <code>*.jar files installed in
<code>$CATALINA_HOME/lib. Therefore classes111.zip
or <code>classes12.zip will need to be renamed with a .jar
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 oracle.jdbc.OracleDriver
rather than <code>oracle.jdbc.driver.OracleDriver as Oracle have stated
that <code>oracle.jdbc.driver.OracleDriver is deprecated and support
for this driver class will be discontinued in the next major release.
</p>
<h3>1. Context configuration
<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. 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.
<source>
<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"/>
</source>
</p>
<h3>2. web.xml configuration
<p>You should ensure that you respect the element ordering defined by the DTD when you
create you applications web.xml file.</p>
<source>
<resource-ref>
<description>Oracle Datasource example</description>
<res-ref-name>jdbc/myoracle</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
</resource-ref>
</source>
<h3>3. Code example
<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>
<source>
Context initContext = new InitialContext();
Context envContext = (Context)initContext.lookup("java:/comp/env");
DataSource ds = (DataSource)envContext.lookup("jdbc/myoracle");
Connection conn = ds.getConnection();
//etc.
</source>
</subsection>
<subsection name="PostgreSQL">
<h3>0. Introduction
<p>PostgreSQL is configured in a similar manner to Oracle.
<h3>1. Required files
<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
<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
<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>This author has not had success here, although others have reported so.
Clarification would be appreciated here.</i>
<source>
<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"/>
</source>
<h4>2b. Application-specific resource configuration
<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.
The Context element should look something like the following.
</p>
<source>
<Context path="/someApp" docBase="someApp"
crossContext="true" reloadable="true" debug="1">
<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"/>
</Context>
</source>
<h3>3. web.xml configuration
<source>
<resource-ref>
<description>postgreSQL Datasource example</description>
<res-ref-name>jdbc/postgres</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
</resource-ref>
</source>
<h4>4. Accessing the datasource
<p>
When accessing the datasource programmatically, remember to prepend
<code>java:/comp/env 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>
<source>
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!");
}
</source>
</subsection>
</section>
<section name="Non-DBCP Solutions">
<p>
These solutions either utilise a single connection to the database (not recommended for anything other
than testing!) or some other pooling technology.
</p>
</section>
<section name="Oracle 8i with OCI client">
<subsection name="Introduction">
<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.
</p>
<p>
After renaming <code>classes12.zip file to classes12.jar
for Tomcat, copy it into <code>$CATALINA_HOME/lib.
You may also have to remove the <code>javax.sql.* classes
from this file depending upon the version of Tomcat and JDK you are using.
</p>
</subsection>
<subsection name="Putting it all together">
<p>
Ensure that you have the <code>ocijdbc8.dll or .so in your $PATH or LD_LIBRARY_PATH
(possibly in <code>$ORAHOME\bin) and also confirm that the native library can be loaded by a simple test program
using <code>System.loadLibrary("ocijdbc8");
</p>
<p>
You should next create a simple test servlet or jsp that has these
<strong>critical lines:
</p>
<source>
DriverManager.registerDriver(new
oracle.jdbc.driver.OracleDriver());
conn =
DriverManager.getConnection("jdbc:oracle:oci8:@database","username","password");
</source>
<p>
where database is of the form <code>host:port:SID Now if you try to access the URL of your
test servlet/jsp and what you get is a
<code>ServletException with a root cause of java.lang.UnsatisfiedLinkError:get_env_handle.
</p>
<p>
First, the <code>UnsatisfiedLinkError 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 $PATH, LD_LIBRARY_PATH problem.
<li>It has been reported that ignoring the driver you have downloded from otn and using
the classes12.zip file from the directory <code>$ORAHOME\jdbc\lib will also work.
</li>
</ul>
</p>
<p>
Next you may experience the error <code>ORA-06401 NETCMN: invalid driver designator
</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) with this one:
<code>(description=(address=(host=myhost)(protocol=tcp)(port=1521))(connect_data=(sid=orcl)))
</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 :-)
</p>
</subsection>
</section>
<section name="Common Problems">
<p>Here are some common problems encountered with a web application which
uses a database and tips for how to solve them.</p>
<subsection name="Intermittent dB Connection Failures">
<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 dB connection is less than the amount
of time garbage collection took you can get a db conneciton failure.
</p>
<p>To collect data on how long garbage collection is taking add the
<code>-verbose:gc argument to your CATALINA_OPTS
environment variable when starting Tomcat. When verbose gc is enabled
your <code>$CATALINA_BASE/logs/catalina.out 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.
</subsection>
<subsection name="Random Connection Closed Exceptions">
<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:
<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>
Here is an example of properly written code to use a db connection
obtained from a connection pool:
<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>
</p>
</subsection>
<subsection name="Context versus GlobalNamingResources">
<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 section of the server
configuration file. A resource placed in the GlobalNamingResources section will be shared
among the Contexts of the server.
</p>
</subsection>
<subsection name="JNDI Resource Naming and Realm Interaction">
<p>
In order to get Realms to work, the realm must refer to the datasource as
defined in the <GlobalNamingResources> or <Context> section, not a datasource as renamed
using <ResourceLink>.
</p>
</subsection>
</section>
</body>
</document>
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