Understanding Application Architecture

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Project File Structure

After the source codes is imported into IDEs, the project file structure looks like the following:

├── .github
│   ├── ISSUE_TEMPLATE
│   │   └── bug_report.md
│   └── workflows
│       └── maven.yml
├── src
│   ├── main
│   │   ├── java
│   │   │   └── com
│   │   │       └── example
│   │   │           ├── GreetingMessage.java
│   │   │           ├── GreetingResource.java
│   │   │           ├── GreetingService.java
│   │   │           └── JaxrsActivator.java
│   │   └── resources
│   │       └── META-INF
│   │           └── beans.xml
│   └── test
│       ├── java
│       │   └── com
│       │       └── example
│       │           ├── it
│       │           │   ├── GreetingResourceTest.java
│       │           │   └── GreetingServiceTest.java
│       │           └── GreetingMessageTest.java
│       └── resources
│           └── arquillian.xml
├── .gitignore
├── LICENSE
├── pom.xml
└── README.md

The .github folder holds the Github specific configurations, eg, issue templates, Github Actions workflows.

The src/main/java includes some sample codes:

• GreetingMessage is a simple POJO to present a greeting message.
• GreetingService is a simple CDI managed bean used to building a greeting message.
• GreetingResource is a simple JAX-RS resource to produce RESTful APIs.
• JaxrsActivator is the JAX-RS application class which is used to activate JAX-RS in Jakarta EE applications.

The src/main/java/resources/META-INF/beans.xml is a CDI configuration file. CDI is activated by default since Java EE 7, so beans.xml file is optional if you do not have any extra CDI configuration.

The src/test/java includes some ample codes for testing purpose. Especially, the tests under com.example.it package is JBoss Arquillian Integration Tests , which means it will deploy into application servers and run the tests.

The src/test/java/resources/arquillian.xml is a JBoss Arquillian sample configuration file.

Application Architecture

A traditional 3-tier application architecture is a modular client-server architecture that consists of a presentation tier, an application tier and a data tier. The three tiers are logical, not physical, and may or may not run on the same physical server.

In our sample application, the presentation tier is not the web pages in traditional web applications, but consists of a collection of RESTful APIs.