Word Count Example Program

Author: Robert Brewer October 2021

Hello! Welcome to my word counter example program!

The project is divided into the following Gradle sub-modules:

• lib - This is the core WordCounter jar
• config - This is some common config e.g. location of chronicles
• common - This defines the common Chronicle message structure
• micro-service - This wraps the WordCounter jar in an event sourced chronicle micro-service
• web-service - This is the REST api to add words and query the count

The web-service submits commands via the command Chronicle queue. The micro-service reads the command, performs the operation and emits a single event. A command always results in an event whether the operation is successful or not.

When the micro-service starts up it reads all commands in the command queue to rebuild its state. Therefore, the count of words will persist until the queues found under ./DATA are deleted or moved.

To test out the web-service & micro-service interaction simply start the applications by running their respective main methods and submit REST commands via curl on the command line as described in the examples below.

Example: Adding a word

rbrewer@wordcount$ curl -i -X POST localhost:7000/add/foo
HTTP/1.1 200 OK
Date: Mon, 18 Oct 2021 16:34:33 GMT
Content-Type: text/plain
Content-Length: 65

!com.alphaedge.wordcount.common.events.WordAdded {
  word: foo
}

Example: Querying a word count

rbrewer@wordcount$ curl -i -X GET localhost:7000/get/foo
HTTP/1.1 200 OK
Date: Mon, 18 Oct 2021 16:35:15 GMT
Content-Type: text/plain
Content-Length: 84

!com.alphaedge.wordcount.common.events.WordCountQueried {
  count: 3,
  word: foo
}

Example: Error on adding word with non-alpha character

rbrewer@wordcount$ curl -i -X POST localhost:7000/add/hello!
HTTP/1.1 200 OK
Date: Mon, 18 Oct 2021 16:44:03 GMT
Content-Type: text/plain
Content-Length: 100

!com.alphaedge.wordcount.common.events.WordAddError {
  error: Unable to add word,
  word: hello!
}