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This package contains two DataSources: PerUserPoolDataSource and
SharedPoolDataSource which provide a database connection pool.
Below are a couple of usage examples. One shows deployment into a JNDI system.
The other is a simple example initializing the pool using standard java code.
JNDI
Most
J2EE containers will provide some way of deploying resources into JNDI. The
method will vary among containers, but once the resource is available via
JNDI, the application can access the resource in a container independent
manner. The following example shows deployment into tomcat (catalina).
In server.xml, the following would be added to the <Context> for your
webapp:
<Resource name="jdbc/bookstore" auth="Container"
type="org.apache.commons.dbcp.datasources.PerUserPoolPoolDataSource"/>
<ResourceParams name="jdbc/bookstore">
<parameter>
<name>factory</name>
<value>org.apache.commons.dbcp.datasources.PerUserPoolDataSourceFactory</value>
</parameter>
<parameter>
<name>dataSourceName</name><value>java:comp/env/jdbc/bookstoreCPDS</value>
</parameter>
<parameter>
<name>defaultMaxActive</name><value>30</value>
</parameter>
</ResourceParams>
In web.xml. Note that elements must be given in the order of the dtd
described in the servlet specification:
<resource-ref>
<description>
Resource reference to a factory for java.sql.Connection
instances that may be used for talking to a particular
database that is configured in the server.xml file.
</description>
<res-ref-name>
jdbc/bookstore
</res-ref-name>
<res-type>
org.apache.commons.dbcp.datasources.PerUserPoolDataSource
</res-type>
<res-auth>
Container
</res-auth>
</resource-ref>
Catalina deploys all objects configured similarly to above within the
java:comp/env namespace. So the JNDI path given for
the dataSourceName parameter is valid for a
ConnectionPoolDataSource that is deployed as given in the
cpdsadapter example
The DataSource is now available to the application as shown
below:
Context ctx = new InitialContext();
DataSource ds = (DataSource)
ctx.lookup("java:comp/env/jdbc/bookstore");
Connection con = null;
try
{
con = ds.getConnection();
...
use the connection
...
}
finally
{
if (con != null)
con.close();
}
The reference to the DataSource could be maintained, for
multiple getConnection() requests. Or the DataSource can be
looked up in different parts of the application code.
PerUserPoolDataSourceFactory and
SharedPoolDataSourceFactory will maintain the state of the pool
between different lookups. This behavior may be different in other
implementations.
Without JNDI
Connection pooling is useful in applications regardless of whether they run
in a J2EE environment and a DataSource can be used within a
simpler environment. The example below shows SharedPoolDataSource using
DriverAdapterCPDS as the backend source, though any CPDS is applicable.
public class Pool
{
private static DataSource ds;
static
{
DriverAdapterCPDS cpds = new DriverAdapterCPDS();
cpds.setDriver("org.gjt.mm.mysql.Driver");
cpds.setUrl("jdbc:mysql://localhost:3306/bookstore");
cpds.setUser("foo");
cpds.setPassword(null);
SharedPoolDataSource tds = new SharedPoolDataSource();
tds.setConnectionPoolDataSource(cpds);
tds.setMaxActive(10);
tds.setMaxWait(50);
ds = tds;
}
public static getConnection()
{
return ds.getConnection();
}
}
This class can then be used wherever a connection is needed:
Connection con = null;
try
{
con = Pool.getConnection();
...
use the connection
...
}
finally
{
if (con != null)
con.close();
}
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