Chapter 4. Sample Applications

The Spring GemFire project includes one sample application. Named "Hello World", the sample demonstrates how to configure and use GemFire inside a Spring application. At runtime, the sample offers a shell to the user allowing him to run various commands against the grid. It provides an excellent starting point for users unfamiliar with the essential components or the Spring and GemFire concepts.

The sample is bundled with the distribution and is Maven-based. One can easily import them into any Maven-aware IDE (such as SpringSource Tool Suite) or run them from the command-line.

4.1. Hello World

The Hello World sample demonstrates the core functionality of the Spring GemFire project. It bootstraps GemFire, configures it, executes arbitrary commands against it and shuts it down when the application exits. Multiple instances can be started at the same time as they will work with each other sharing data without any user intervention.

4.1.1. Starting and stopping the sample

Hello World is designed as a stand-alone java application. It features a Main class which can be started either from your IDE of choice (in Eclipse/STS through Run As/Java Application) or from the command line through Maven using mvn exec:java. One can also use java directly on the resulting artifact if the classpath is properly set.

To stop the sample, simply type exit at the command line or press Ctrl+C to stop the VM and shutdown the Spring container.

4.1.2. Using the sample

Once started, the sample will create a shared data grid and allow the user to issue commands against it. The output will likely look as follows:

INFO: Created GemFire Cache [Spring GemFire World] v. X.Y.Z
INFO: Created new cache region [myWorld]
INFO: Member xxxxxx:50694/51611 connecting to region [myWorld]
Hello World!
Want to interact with the world ? ...
Supported commands are:

get <key> - retrieves an entry (by key) from the grid
put <key> <value> - puts a new entry into the grid
remove <key> - removes an entry (by key) from the grid

For example to add new items to the grid one can use:

-> put 1 unu
INFO: Added [1=unu] to the cache
-> put 1 one
INFO: Updated [1] from [unu] to [one]
-> size
-> put 2 two
INFO: Added [2=two] to the cache
-> size

Multiple instances can be created at the same time. Once started, the new VMs automatically see the existing region and its information:

INFO: Connected to Distributed System ['Spring GemFire World'=xxxx:56218/49320@yyyyy]
Hello World!

-> size
-> map
[2=two] [1=one]
-> query length = 3
[one, two]

Experiment with the example, start (and stop) as many instances as you want, run various commands in one instance and see how the others react. To preserve data, at least one instance needs to be alive all times - if all instances are shutdown, the grid data is completely destroyed (in this example - to preserve data between runs, see the GemFire documentations).

4.1.3. Hello World Sample Explained

Hello World uses both Spring XML and annotations for its configuration. The initial boostrapping configuration is app-context.xml which includes the cache configuration, defined under cache-context.xml file and performs classpath scanning for Spring components. The cache configuration defines the GemFire cache, region and for illustrative purposes a simple cache listener that acts as a logger.

The main beans are HelloWorld and CommandProcessor which rely on the GemfireTemplate to interact with the distributed fabric. Both classes use annotations to define their dependency and life-cycle callbacks.