geode-docs/developing/events/cache_event_handler_examples.html.md.erb

---
title:  Cache Event Handler Examples
---

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Some examples of cache event handlers.

## <a id="cache_event_handler_examples__section_F2790678E9DE4A81B73A4B6346CB210B" class="no-quick-link"></a>Declaring and Loading an Event Handler with Parameters

This declares an event handler for a region in the `cache.xml`. The handler is a cache listener designed to communicate changes to a DB2 database. The declaration includes the listener’s parameters, which are the database path, username, and password.

``` pre
<region name="exampleRegion"> 
  <region-attributes> 
  . . . 
    <cache-listener> 
      <class-name>JDBCListener</class-name> 
      <parameter name="url"> 
        <string>jdbc:db2:SAMPLE</string> 
      </parameter> 
      <parameter name="username"> 
        <string>gfeadmin</string> 
      </parameter> 
      <parameter name="password"> 
        <string>admin1</string> 
      </parameter> 
    </cache-listener> 
  </region-attributes> 
  </region>
```

This code listing shows part of the implementation of the `JDBCListener` declared in the `cache.xml`. This listener implements the `Declarable` interface. When an entry is created in the cache, this listener’s `afterCreate` callback method is triggered to update the database. Here the listener’s properties, provided in the `cache.xml`, are passed into the `Declarable.init` method and used to create a database connection.

``` pre
. . .
public class JDBCListener
extends CacheListenerAdapter
implements Declarable {
  public void afterCreate(EntryEvent e) {
  . . .
    // Initialize the database driver and connection using input parameters
    Driver driver = (Driver) Class.forName(DRIVER_NAME).newInstance();
    Connection connection =
      DriverManager.getConnection(_url, _username, _password);
      System.out.println(_connection);
        . . .
  }
    . . .
  public void init(Properties props) {
    this._url = props.getProperty("url");
    this._username = props.getProperty("username");
    this._password = props.getProperty("password");
  }
}
```

## <a id="cache_event_handler_examples__section_2B4275C1AE744794AAD22530E5ECA8CC" class="no-quick-link"></a>Installing an Event Handler Through the API

This listing defines a cache listener using the `RegionFactory` method `addCacheListener`.

``` pre
Region newReg = cache.createRegionFactory()
          .addCacheListener(new SimpleCacheListener())
          .create(name);
 
```

You can create a cache writer similarly, using the `RegionFactory` method `setCacheWriter`, like this:

``` pre
Region newReg = cache.createRegionFactory()
          .setCacheWriter(new SimpleCacheWriter())
          .create(name);
 
```

## <a id="cache_event_handler_examples__section_C62E9535C43B4BC5A7AA7B8B4125D1EB" class="no-quick-link"></a>Installing Multiple Listeners on a Region

XML:

``` pre
<region name="exampleRegion">
  <region-attributes>
    . . .
    <cache-listener>
      <class-name>myCacheListener1</class-name>
    </cache-listener>
    <cache-listener>
      <class-name>myCacheListener2</class-name>
    </cache-listener>
    <cache-listener>
      <class-name>myCacheListener3</class-name>
    </cache-listener>
  </region-attributes>
</region>
```

API:

``` pre
CacheListener listener1 = new myCacheListener1(); 
CacheListener listener2 = new myCacheListener2(); 
CacheListener listener3 = new myCacheListener3(); 

Region nr = cache.createRegionFactory()
  .initCacheListeners(new CacheListener[]
    {listener1, listener2, listener3})
  .setScope(Scope.DISTRIBUTED_NO_ACK)
  .create(name);
```

## <a id="cache_event_handler_examples__section_3AF3D7C9927F491F8BACDB72834E42AA" class="no-quick-link"></a>Installing a Write-Behind Cache Listener

``` pre
//AsyncEventQueue with listener that performs WBCL work
<cache>
   <async-event-queue id="sampleQueue" persistent="true"
    disk-store-name="exampleStore" parallel="false">
      <async-event-listener>
         <class-name>MyAsyncListener</class-name>
         <parameter name="url"> 
           <string>jdbc:db2:SAMPLE</string> 
         </parameter> 
         <parameter name="username"> 
           <string>gfeadmin</string> 
         </parameter> 
         <parameter name="password"> 
           <string>admin1</string> 
         </parameter> 
               </async-event-listener>
             </async-event-queue>

// Add the AsyncEventQueue to region(s) that use the WBCL
  <region name="data">
       <region-attributes async-event-queue-ids="sampleQueue">
    </region-attributes>
  </region>
</cache>
```