geode-docs/basic_config/the_cache/setting_cache_initializer.html.md.erb

---
title:  Launching an Application after Initializing the Cache
---

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You can specify a callback application that is launched after the cache initialization.

By specifying an `<initializer>` element in your cache.xml file, you can trigger a callback application, which is run after the cache has been initialized. Applications that use the cacheserver script to start up a server can also use this feature to hook into a callback application. To use this feature, you need to specify the callback class within the `<initializer>` element. This element should be added to the end of your `cache.xml` file.

You can specify the `<initializer>` element for either server caches or client caches.

The callback class must implement the `Declarable` interface. When the callback class is loaded, its `init` method is called, and any parameters defined in the `<initializer>` element are passed as properties.

The following is an example specification.

In cache.xml:

``` pre
<initializer>
   <class-name>MyInitializer</class-name>
      <parameter name="members">
         <string>2</string>
      </parameter>
</initializer>
```

Here's the corresponding class definition:

``` pre
 
import org.apache.geode.cache.Declarable;

public class MyInitializer implements Declarable {
   public void init(Properties properties) {
      System.out.println(properties.getProperty("members"));
   }
}
```

The following are some additional real-world usage scenarios:

1.  Start a SystemMembershipListener

    ``` pre
    <initializer>
       <class-name>TestSystemMembershipListener</class-name>
    </initializer>
    ```

2.  Write a custom tool that monitors cache resources

    ``` pre
    <initializer>
       <class-name>ResourceMonitorCacheXmlLoader</class-name>
    </initializer>
    ```

Any singleton or timer task or thread can be instantiated and started using the initializer element.