http://tomcat.apache.org/tomcat-6.0-doc/jndi-datasource-examples-howto.html
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.
See the DBCP documentation for a complete list of configuration parameters.
| Installation |
DBCP uses the Commons Database Connection Pool. It relies on number of Commons components:
- Commons DBCP
- Commons Pool
These libraries are located in a single JAR at $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.
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| Preventing dB connection pool leaks |
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.
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 db connection pool "leak". This can eventually result in your web application db connections failing if there are no more available connections.
There is a solution to this problem. 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.
To configure a DBCP DataSource so that abandoned dB connections are removed and recycled add the following attribute to the Resource configuration for your DBCP DataSource:
When available db connections run low DBCP will recover and recycle any abandoned dB connections it finds. The default is false.
Use the removeAbandonedTimeout attribute to set the number of seconds a dB connection has been idle before it is considered abandoned.
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removeAbandonedTimeout="60"
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The default timeout for removing abandoned connections is 300 seconds.
The 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.
The default is false.
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| MySQL DBCP Example |
0. Introduction
Versions of MySQL and JDBC drivers that have been reported to work:
- MySQL 3.23.47, MySQL 3.23.47 using InnoDB,, MySQL 3.23.58, MySQL 4.0.1alpha
- Connector/J 3.0.11-stable (the official JDBC Driver)
- mm.mysql 2.0.14 (an old 3rd party JDBC Driver)
Before you proceed, don't forget to copy the JDBC Driver's jar into $CATALINA_HOME/lib.
1. MySQL configuration
Ensure that you follow these instructions as variations can cause problems.
Create a new test user, a new database and a single test table. Your MySQL user must have a password assigned. The driver will fail if you try to connect with an empty password.
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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);
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Note: the above user should be removed once testing is complete!
Next insert some test data into the testdata table.
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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>
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2. Context configuration
Configure the JNDI DataSource in Tomcat by adding a declaration for your resource to your Context.
For example:
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<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 -1 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.
-->
<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"/>
</Context>
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3. web.xml configuration
Now create a WEB-INF/web.xml for this test application.
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<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>
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4. Test code
Now create a simple test.jsp page for use later.
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<%@ 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>
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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.
Finally deploy your web app into $CATALINA_BASE/webapps either as a warfile called DBTest.war or into a sub-directory called DBTest
Once deployed, point a browser at http://localhost:8080/DBTest/test.jsp to view the fruits of your hard work.
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