org.apache.avalon.excalibur.datasource
Class ResourceLimitingJdbcDataSource

java.lang.Object
  org.apache.avalon.framework.logger.AbstractLogEnabled
      org.apache.excalibur.instrument.AbstractLogEnabledInstrumentable
          org.apache.avalon.excalibur.datasource.ResourceLimitingJdbcDataSource

All Implemented Interfaces:

Component, Configurable, DataSourceComponent, Disposable, Instrumentable, LogEnabled, ThreadSafe

public class ResourceLimitingJdbcDataSource

extends AbstractLogEnabledInstrumentable

implements DataSourceComponent, Disposable

The ResourceLimiting implementation for DataSources in Avalon. This uses the normal java.sql.Connection object and java.sql.DriverManager.

This datasource pool implementation is designed to make as many database connections as are needed available without placing undo load on the database server.

If an application under normal load needs 3 database connections for example, then the max pool size should be set to a value like 10. This will allow the pool to grow to accomodate a sudden spike in load without allowing the pool to grow to such a large size as to place undo load on the database server. The pool's trimming features will keep track of how many connections are actually needed and close those connections which are no longer required.

Configuration Example:

   <rl-jdbc>
     <pool-controller max="10" max-strict="true"
       blocking="true" timeout="-1"
       trim-interval="60000" auto-commit="true"
       connection-class="my.overrided.ConnectionClass">
       <keep-alive disable="false" age="5000">select 1</keep-alive>
     </pool-controller>
     <driver>com.database.jdbc.JdbcDriver</driver>
     <dburl>jdbc:driver://host/mydb</dburl>
     <user>username</user>
     <password>password</password>
   </rl-jdbc>
 

Roles Example:

   <role name="org.apache.avalon.excalibur.datasource.DataSourceComponentSelector"
     shorthand="datasources"
     default-class="org.apache.avalon.excalibur.component.ExcaliburComponentSelector">
     <hint shorthand="rl-jdbc"
       class="org.apache.avalon.excalibur.datasource.ResourceLimitingJdbcDataSource"/>
   </role>
 

Configuration Attributes:

• The max attribute is used to set the maximum number of connections which will be opened. See the blocking attribute. (Defaults to "3")
• The max-strict attribute is used to determine whether or not the maximum number of connections can be exceeded. If true, then an exception will be thrown if more than max connections are requested and blocking is false. (Defaults to "true")
  WARNING: In most cases, this value should always be set to true. Setting it to false means that under heavy load, your application may open a very large number of connections to the database. Some database servers behave very poorly under large connection loads and can even crash.
• The blocking attributes is used to specify the behavior of the DataSource pool when an attempt is made to allocate more than max concurrent connections. If true, the request will block until a connection is released, otherwise, a NoAvailableConnectionException will be thrown. Ignored if max-strict is false. (Defaults to "true")
• The timeout attribute is used to specify the maximum amount of time in milliseconds that a request for a connection will be allowed to block before a NoAvailableConnectionException is thrown. A value of "0" specifies that the block will never timeout. (Defaults to "0")
• The trim-interval attribute is used to specify how long idle connections will be maintained in the pool before being closed. For a complete explanation on how this works, see ResourceLimitingPool.trim() (Defaults to "60000", 1 minute)
• The auto-commit attribute is used to determine the default auto-commit mode for the Connections returned by this DataSource.
• The connection-class attribute is used to override the Connection class returned by the DataSource from calls to getConnection(). Set this to "org.apache.avalon.excalibur.datasource.Jdbc3Connection" to gain access to JDBC3 features. Jdbc3Connection does not exist if your JVM does not support JDBC3. (Defaults to "org.apache.avalon.excalibur.datasource.JdbcConnection")
• The keep-alive element is used to override the query used to monitor the health of connections. If a connection has not been used for 5 seconds then before returning the connection from a call to getConnection(), the connection is first used to ping the database to make sure that it is still alive. Setting the disable attribute to true will disable this feature. Setting the age allows the 5 second age to be overridden. (Defaults to a query of "SELECT 1" and being enabled)
• The driver element is used to specify the driver to use when connecting to the database. The specified class must be in the classpath. (Required)
• The dburl element is the JDBC connection string which will be used to connect to the database. (Required)
• The user and password attributes are used to specify the user and password for connections to the database. (Required)

Since:

4.1

Version:

CVS $Revision: 1.5 $ $Date: 2004/03/30 15:58:50 $

Author:

Avalon Development Team

Field Summary

protected InstrumentedResourceLimitingPool

m_pool

Fields inherited from interface org.apache.avalon.excalibur.datasource.DataSourceComponent

ROLE

Fields inherited from interface org.apache.excalibur.instrument.Instrumentable

EMPTY_INSTRUMENT_ARRAY, EMPTY_INSTRUMENTABLE_ARRAY

Constructor Summary

ResourceLimitingJdbcDataSource()

Method Summary

void	configure(Configuration configuration) Pass the Configuration to the Configurable class.
void	dispose() The dispose operation is called at the end of a components lifecycle.
java.sql.Connection	getConnection() Gets the Connection to the database

Methods inherited from class org.apache.excalibur.instrument.AbstractLogEnabledInstrumentable

addChildInstrumentable, addInstrument, getChildInstrumentables, getInstrumentableName, getInstruments, setInstrumentableName

Methods inherited from class org.apache.avalon.framework.logger.AbstractLogEnabled

enableLogging, getLogger, setupLogger, setupLogger, setupLogger

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

m_pool

protected InstrumentedResourceLimitingPool m_pool

Constructor Detail

ResourceLimitingJdbcDataSource

public ResourceLimitingJdbcDataSource()

Method Detail

getConnection

public java.sql.Connection getConnection()
                                  throws java.sql.SQLException

Gets the Connection to the database

Specified by:

getConnection in interface DataSourceComponent

Returns:

Connection a valid connection for you to use

Throws:

NoValidConnectionException - when there is no valid Connection wrapper available in the classloader.

NoAvailableConnectionException - when there are no more available Connections in the pool.

java.sql.SQLException

configure

public void configure(Configuration configuration)
               throws ConfigurationException

Pass the Configuration to the Configurable class. This method must always be called after the constructor and before any other method.

Specified by:

configure in interface Configurable

Parameters:

configuration - the class configurations.

Throws:

ConfigurationException - if an error occurs

dispose

public void dispose()

The dispose operation is called at the end of a components lifecycle. This method will be called after Startable.stop() method (if implemented by component). Components use this method to release and destroy any resources that the Component owns.

Specified by:

dispose in interface Disposable