How to invoke init method when Gemfire region gets created via Spring Data Gemfire?

Question

I am successfully able to create a Gemfire region using Spring Data Gemfire like below -

<gfe:replicated-region id="myRegion" name="regionName"/>

I now want to load data automatically into my region as soon as it gets created. So, I thought maybe I can define a init method in the region's spring settings. But it is not allowing me to do so.

<gfe:replicated-region id="myRegion" name="regionName">
    <gfe:init-method>
        <ref bean="initLoader"/>
    </gfe:init-method>
</gfe:replicated-region>

Can you please tell me how can I achieve this? Thanks!

Answer 1

Right, the SDG core XML namespace (source here) is not going to allow you to do that. However, you do have several options.

1. First, you can use GemFire's Snapshot Service, for which Spring Data GemFire provides support.

2. Second, you could create a Spring BeanPostProcessor (relevant docs here) to process the desired Region after initialization to load up some data.

I have an example of such a BeanPostProcessor here, configured here, and used in this test class. This is a pretty simplistic example as it is only using another Map to populate the Region (i.e. RegionTwo), but you could image the "regionData" being any source you prefer, such as your initLoader.

WARNING: You do have to be careful about injecting other beans into a Spring BeanPostProcessors as mentioned in the docs (3rd note down) as you could possibly cause a series of premature bean instantiations that are not subject to the Spring container post processing activities, such as proxying for concerns like Transaction Management. So be careful.

3. It is also possible to implement and register a Spring ApplicationListener in the Spring application context that is autowired with the Region to load, the data source to load the Region with, that then performs the Region data hydrating actions on the ContextRefreshedEvent.

Something like...

<bean class="org.example.app.event.MyContextRefreshedEventListener"/>

Where MyContextRefreshedEventListener is defined like so...

package org.example.app.event;

import ...;

class MyContextRefreshedEventListener 
    extends ApplicationListener<ContextRefreshedEvent> {

  @Resource(name = "RegionToLoad")
  Region<?, ?> regionToLoad;

  // Data Source used to hydrate/load the Region on startup
  @Autowired
 DataSource dataSource;

 public void onApplicationEvent(ContextRefreshedEvent event) {
    // load the Region using DataSource
  }
}

When the Spring container startups and is refreshed, after all the beans have been initialized, this ApplicationListener, when registered as a "bean" in the Spring ApplicationContext, will get fired by Spring specifically for the ContextRefreshedEvent, which will then load your Region.

There are other options too, if you do not need to load your Region in advance, like using read-through, on-demand cache Region loading with GemFire's CacheLoader functionality (docs here). Though, as I mentioned, a CacheLoader is only fired when a cache miss occurs, still, you could code your CacheLoader as to load a block of data based on some heuristics (application data access patterns) in addition to returning the single entry miss.

Anyway, you will find that there really is not shortage of ways to do what you are asking.

If you have more specific questions with the information above, let me know.

Hope this helps!

Cheers, John