Applied Domain-Driven Design Blueprints for Java EE
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Cargo Tracker - Domain-Driven Design Blueprints for Java EE

Overview

The project demonstrates how you can develop applications with the Java EE platform using widely adopted architectural best practices like Domain-Driven Design (DDD). The project is directly based on the well known original Java DDD sample application developed by DDD pioneer Eric Evans' company Domain Language and the Swedish software consulting company Citerus. The cargo example actually comes from Eric Evans' seminal book on DDD. The original application is written in Spring, Hibernate and Jetty whereas this application is build entirely on Java EE 8.

The application is an end-to-end system for keeping track of shipping cargo. It has several interfaces described in the following sections.

For further details on the project, please visit: https://m-reza-rahman.github.io/cargo-tracker/

Getting Started

The project site has detailed information on how to get started, especially with NetBeans.

The simplest steps are the following (no IDE required):

To set up in NetBeans, follow these steps:

  • Set up JDK 8+, NetBeans 8.2+ and Payara 5+.
  • Open the source code directory in NetBeans - it's just a Maven project, NetBeans will do the rest for you. As noted in the site instructions on NetBeans, you may get a few spurious errors due to reported NetBeans bugs. Just ignore them and proceed with clean/building the application.
  • After the project is built (which will take a while the very first time as Maven downloads dependencies), simply run it via Payara 5.

It's best to use Chrome for the application since it has the best support for HTML 5 forms, but any HTML 5 capable browser is fine.

Exploring the Application

After the application runs, it will be available at: http://localhost:8080/cargo-tracker/. Under the hood, the application uses a number of Java EE (and Java EE 7) features including JSF 2.2, CDI, EJB 3.2, JPA 2.1, JAX-RS 2, WebSocket, JSON-P, Bean Validation 1.1 and JMS 2.

There are several web interfaces, REST interfaces and a file system scanning interface. It's probably best to start exploring the interfaces in the rough order below.

The tracking interface let's you track the status of cargo and is intended for the general public. Try entering a tracking ID like ABC123 (the application is pre-populated with some sample data).

The administrative interface is intended for the shipping company that manages cargo. The landing page of the interface is a dashboard providing an overall view of registered cargo. You can book cargo using the booking interface. One cargo is booked, you can route it. When you initiate a routing request, the system will determine routes that might work for the cargo. Once you select a route, the cargo will be ready to process handling events at the port. The administrative interface also includes a live map that updates itself as cargo data is updated.

The event logging interface is intended for port personnel registering what happened to cargo. The interface is primarily intended for mobile devices, but you can use it via a desktop browser. The interface is accessible at: http://localhost:8080/cargo-tracker/mobile.xhtml. For convenience, you could use a mobile emulator instead of an actual mobile device. On Windows, you can use Microsoft WebMatrix for device emulation. Generally speaking cargo goes though these events:

  • It's received at the origin port.
  • It's loaded and unloaded onto voyages on it's itinerary.
  • It's claimed at it's destination port.
  • It may go through customs at arbitrary points.

While filling out the event registration form, it's best to have the itinerary handy. You can access the itinerary for registered cargo via the admin interface. The cargo handling is done via JMS for scalability and the event notification to the system happens via the CDI event bus and WebSocket, so you will see a visible delay of a few milliseconds after registering the event for the dashboard and live map to update. While using the event logger, note that only the load and unload events require as associated voyage.

You should also explore the file system based bulk event registration interface. It reads files under /tmp/uploads. The files are just CSV files. A sample CSV file is available under /src/test/resources/handling_events.csv. You will need to update the sample to match a registered cargo with a commited itinerary (should be fairly easy to do if you pick cargo ABC123). Sucessfully processed entries are archived under /tmp/archive. Any failed records are archived under /tmp/failed.

Don't worry about making mistakes. The application is intended to be fairly error tolerant. If you do come across issues, you should report them. Please see the Getting Involved section on how to do so.

Note: All data entered is wiped upon application restart, so you can start from a blank slate easily if needed.

You can also use the soapUI scripts included in the source code to explore the REST interfaces as well as the numerous unit tests covering the code base generally.

Exploring the Code

As mentioned earlier, the real point of the application is demonstrating how to create well architected, effective Java EE applications. To that end, once you have gotten some familiarity with the application functionality the next thing to do is to dig right into the code.

DDD is a key aspect of the architecture, so it's important to get at least a working understanding of DDD. As the name implies, Domain-Driven Design is an approach to software design and development that focuses on the core domain and domain logic.

We have a brief overview of DDD specifically as it relates to Java EE on the project site. There's also a resources section in the documentation that you should take a look at. The documentation has sections dedicated to explaining the core constructs of DDD and how they are implemented in the application using Java EE as well as the DDD layers in the application.

For the most part, it's fine if you are new to Java EE. As long as you have a basic understanding of server-side applications, the resources referenced above and the code should be good enough to get started. For learning Java EE further, we have recommended a few links in the resources section of the documentation. Of course, the ideal user of the project is someone who has a basic working understanding both Java EE and DDD. Though it's not our goal to become a kitchen sink example for demonstrating the vast amount of APIs and features in Java EE, we do use a very representative set. You'll find that you'll learn a fair amount by simply digging into the code to see how things are implemented.

Getting Involved

Cargo Tracker is an open source project hosted on GitHub. We would welcome any and all contributions.

You can also send an email to reza_rahman at lycos dot com with any questions, concerns or suggestions.