Project Spring DDD Bank

A sample project following Domain Driven Design with Spring Data JPA

                                        (C) Christoph Knabe, 2017-03-17 ... 2018-10-11

In this project I am trying to apply principles of Domain Driven Design. In contrary to full-blown DDD examples on the web I am applying here some simplifications. This sample application is used for a course on Software Engineering at Beuth University of Applied Sciences Berlin.

This project uses

• JDK 8
• Maven 3
• Spring Boot
• Spring Data + JPA + Hibernate + Derby
• AspectJ Compile Time Weaving for main sources

• springfox-swagger

  for generating documentation and user interface for the REST service
• JUnit 4
• The Exception Handling and Reporting Framework MulTEx

Detailed version indications you can find in the file

pom.xml

By

mvn clean test

After this is working you can import the Maven project into your Java IDE (Spring Tool Suite is recommended, as AspectJ weaving is needed for the compile phase).

You can run the application (a REST server) in your IDE by running class

de.beuth.knabe.spring_ddd_bank.Application

mvn package

java -jar target/spring-ddd-bank-0.1-SNAPSHOT.jar

Which DDD principles are implemented?

• Modelling the domain layer as one package, which does not depend on any other package besides standard Java SE packages as

  java.time

  and

  javax.persistence

  . The latter only for the JPA annotations.

• Avoid an anemic domain model by having relevant business logic methods in entity class

  Client

  .
  This requires the feature Domain Object Dependency Injection (DODI), which can only be implemented by using full AspectJ compile-time weaving. See §11.8.1 Using AspectJ to dependency inject domain objects with Spring.

• The Domain Layer references required services only by self-defined, minimal interfaces (in package

  domain.imports

  ).

• Implementing required services in the infrastructure layer (in package

  infrastructure

  ).

• Linking together required services and their implementations by Dependency Injection.

• Implementing an interface layer for external access to the application. This is implemented as a REST service in package

  rest_interface

  .

Other Characteristics

• It is a little bank application, where the bank can create clients and clients can create and manage accounts, e.g. deposit and transfer money.
• The analysis class diagram is in file src/doc/BankModel.pdf. Its editable source by UMLet has extension

  .uxf

  .
• An overview of the REST endpoints is given at src/doc/REST-API.md. Additionally when running the REST service, the REST endpoint documentation generated by Swagger, is accessible at http://localhost:8080/ and clicking on REST API documentation.
  
• As simplification an application layer is not implemented, but the interface layer is made transactional.
• Internationalizable, parameterizable exception message texts
• Capture of each exception message text in the reference language directly as main JavaDoc comment of the exception
• The application runs against a file-based Derby database. This is configured in file src/main/resources/application.properties
• Tests are run against an empty in-memory Derby database. This is configured in file src/test/resources/application.properties
• Generation of a test coverage report by the JaCoCo Maven plugin into target/site/jacoco-ut/index.html.
• Simple Spring Security with a fixed number of predefined users (1 bank, and 4 clients).

Where are the exception message texts?

In the file

MessageText.properties

src/main/resources/

compile

target/classes/

process-classes

src/main/java/

ExceptionMessagesDoclet

maven-javadoc-plugin

target/classes/

pom.xml

Plans

• Make

  Amount

  a better value object by freezing its attributes. Seems, that for this goal Hibernate has to be used instead of JPA.
• Nice to have: Avoid own ID of

  AccountAccess

  , because this class models an m:n association between

  Client

  and

  Account

  . There should not be a possibility for several links between a client and an account. This would require the usage of

  client.id

  and

  account.id

  as a composite ID for

  AccountAccess

  . Not so easy, see JPA: How to associate entities with relationship attributes?
• Implement another kind of persistence interface beside Spring Data JPA, e.g. JPA Criteria API, as the interface-based implementation of Spring Data is confusing to beginners.
• Implementation of real unit tests with mock implementations of the repository interfaces.

References and Sources

• Detailed example text about DDD
• The DDD Sample project, from which are taken some inspirations
• The Ports and Adapters Pattern
• Can DDD be Adequately Implemented Without DI and AOP?
• Spring Boot
• Spring Dependency Injection
• Spring Data JPA
• Spring Data JPA Query Methods
• This application implements my knowledge about layering and data access at a given point of time. Previous versions were in a 3-layer form in german under Bank3Tier - Bankanwendung in 3 Schichten.