The Carbon Java Framework  

The Carbon Core Component Subsytem

Programmatic Reconfiguration

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Author: Jordan Reed (jreed at
Version: $Revision: 1.1 $($Author: dvoet $ / $Date: 2003/09/23 16:49:49 $)
Created: August 2003


This document details the steps the process of changing a component's configuration at runtime using the Carbon APIs.

Manual configuration changes should be done using JMX with Management Module of Carbon.

Retrieving a Component's Configuration

When a component starts up, it gets its own copy of its configuration object. That copy is managed by the config interceptor. This means that altering a config object by looking it up with the Config API and calling setters on it will not affect the copy of configuration used by the component.

The proper mechanism for altering the settings of a running component are by utilizing the features of its config interceptor. Through the magic of the ConfigurationInterceptor , you can directly cast a component to its specific configuration implementation and make updates to its configuration. Then you can make cast the component to the ConfigurationInterceptor and make calls to apply the configuration.

Just setting the values of a component configuration will not immediately alter the behavior of the component. Internally, once you start altering the configuration of a component, it actually creates a working copy, rather than directly altering the settings of the live component. The ConfigurationInterceptor.applyConfiguration() method then causes the lifecycle action to pause calls to the component while it reconfigures with the new settings. This allows you to set many different properties that may be interdependent as an atomic operation.

StatementFactory Example

Here is an example of reconfiguring the ConnectionFactory associated with a StatementFactory. This could be used to swap between a test and live databases during runtime, for database failover, etc.

StatementFactory Example

// Lookup the component to reconfigure
StatementFactory statementFactory =
  (StatementFactory) Lookup.getInstance().fetchComponent("/sql/MyStatementFactory");

// Lookup the service you would like to set as the value
ConnectionFactory namedConnectionFactory =
  (ConnectionFactory) Lookup.getInstance().fetchComponent("/sql/NamedConnectionFactory");

// Register the new service with the component
((StatementFactoryConfiguration) statementFactory).setConnectionFactory(namedConnectionFactory);

// Have the component reconfigure itself to start using the new settings
((ConfigurationInterceptor) statementFactory).applyConfiguration();

You'll also notice the ConfigurationInterceptor.persistConfiguration method on the ConfigurationInterceptor . When called, that method will take the current settings for the component and write them out to the configuration service. This would be used to store the configurations for later use (after restart). If not called, the file on disk will not be altered and the component will revert to the original configuration after restart.

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