The Command Pattern Example

Prerequisites

To run this example the Oracle Coherence Incubator must be built and installed locally. Instructions on how to achieve this are located here: Building the Oracle Coherence Incubator.

Source Code

The source code for this example is located in the coherence-commandpattern-examples module of the Oracle Coherence Incubator.

Overview

The Command Pattern example demonstrates how to use the Command Pattern to set the value of an attribute on a Command Context asynchronously. It illustrates the three main elements of the Command Pattern, A Context, the CommandSubmitter and a Command.

There are four classes in the example:

1. CommandPatternExample - The main application class.

2. GenericContext - An mutable implementation of the Context interface that will hold a specific type of object.

3. LoggingCommand - A Command that will write a log message to the Coherence logs.

4. SetValueCommand - A Command that will call the setValue() method on the GenericContext.

The CommandPatternExample creates a new GenericContext (that holds a Long) which is registered with the ContextsManager. The example then submits a LoggingCommand stating that the application has commenced. In a tight loop, the value of the Long is set 10000 times using the SetValueCommand. After each 1000th iteration a PriorityCommand is submitted to log what number the iteration is at.

There are two approaches to running the example. First is using a simple entirely encapuslated approach. The second is using a client-server mode in which an Coherence Extend-based Client runs the actual CommandPatternExample, backed by a Coherence Proxy-enabled Server the hosts the GenericContext.

The following instructions assume that $COHERENCE_INCUBATOR is the directory in which the Oracle Coherence Incubator source code has been downloaded, unpacked and built according to the prerequisites outlined above.

Running the Simple Example

Execute the following shell commands to run the Simple Example.

In a new Terminal / Shell Console for the "Example"

1. Change to the Command Pattern Examples directory.

   cd $COHERENCE_INCUBATOR/coherence-commandpattern-examples/target

2. Run the Simple Example

   java -jar coherence-commandpattern-examples-11.0.0.jar simple.properties

You will notice that the application will output logs showing the iteration and logging of priority commands.

Running in Client-Server Mode

Execute the following shell commands to run the example in Client-Server Mode.

In a new Terminal / Shell Console for the "Server"

1. Change to the Command Pattern Examples directory.

   cd $COHERENCE_INCUBATOR/coherence-commandpattern-examples/target

2. Start the Coherence Server (and Proxy) Process/

   java -jar coherence-commandpattern-examples-11.0.0.jar server.properties

In a new Terminal / Shell Console for the "Client"

1. Change to the Command Pattern Examples directory.

   cd $COHERENCE_INCUBATOR/coherence-commandpattern-examples/target

2. Start the Coherence Extend-based Client Application (example)

   java -jar coherence-commandpattern-examples-11.0.0.jar client.properties

You will notice the "Server" console that the logging commands are executing in the server, where are the "Client" console displays no such logging. This is because the Commands are executed at the Context, that of which is hosted by the "Server".

After this you may kill the "Server" application and close the consoles.