WebSphere eXtreme Scale Best Practices for Operation and Management

106 WebSphere eXtreme Scale Best Practices for Operation and Management

throws IOException {

Date date = (Date)value;

out.writeLong(date.getTime());

}

}

The final step is to configure our ExampleOptimisticCallbackImpl class so that WebSphere

eXtreme Scale knows to use it. Example 5-18 shows how we can change an objectgrid.xml

to achieve this configuration (the parts in italics are the changes).

Example 5-18 ExampleOptimisticCallbackImpl class

…

<objectGrids>

<objectGrid name="MyGrid">

<backingMap name="MyBackingMap" readOnly="false" lockStrategy="OPTIMISTIC"

pluginCollectionRef="MyBackingMapPlugins"/>

…

</objectGrids>

<backingMapPluginCollections>

<backingMapPluginCollection id="MyBackingMapPlugins">

<bean id="OptimisticCallback"

className="com.mycorp.myapp.ExampleOptimisticCallbackImpl"/>

…

5.4.3 MapEventListener plug-ins

A MapEventListener is a plug-in that allows you to execute custom logic when certain events

happen. If you want to be notified whenever an entry is evicted (for whatever reason, such as

if the time-to-live value that you configured has expired), you can write a MapEventListener

implementation that will be called when an entry is evicted.

Example 5-19 shows an example of a simple MapEventListener, which logs to SystemOut.log

when various methods are called.

Example 5-19 Example MapEventListener

import java.util.Date;

import com.ibm.websphere.objectgrid.plugins.MapEventListener;

public class ExampleMapEventListener implements MapEventListener {

public void entryEvicted(Object key, Object value) {

System.out.println("ExampleMapEventListener: At " + new Date() + " an entry

with key " + key + " and value " + value + " has been evicted.");

}

public void preloadCompleted(Throwable arg0) {

// Not much interesting to do here

}

}

To configure your grid so that this MapEventListener is used, you must modify your

ObjectGrid descriptor XML file (the deployment XML file does not have to be modified) to

resemble Example 5-20 on page 107 (the changes are in italics).