What are java three-tier architecture and DDD hierarchical architecture?

Three-tier architecture

The traditional three-tier architecture is mainly divided into business interface layer, business logic layer, and data access layer

• Business interface layer: Mainly the definition of API, including resource path definition, request message acceptance, response message return, request encoding, etc.;

• Business logic layer: Mainly doing business logic processing, this layer includes data mapping DTO to VO, writing core business logic, combining different data warehouses, and doing business logic;

• # Data access layer: mainly doing data storage , including data mapping VO to PO, definition of data interface, and writing of mapping XML.

DDD layered architecture

The DDD layered architecture can also be called a four-layer architecture, which mainly consists of the user interface layer, application layer, domain layer, and basic layer;

• User interface layer: Responsible for displaying information to users and interpreting user instructions, such as users, programs, automation scripts, batch scripts, etc.;

• Application layer: Mainly used to coordinate multiple aggregated services and domain objects to complete service orchestration and combination. It can adjust local or remote services, including authority verification, transaction control, anti-duplication, etc. , don’t put the core business logic here;

• Domain layer: implements the core logic, including aggregate roots, entities, value objects, domain services, including business extension points and verification rules , combined aggregation services and other related functions;

• Basic layer: Provides common technologies and basic services, including some third-party tools, caches, databases, files, etc., using a dependency inversion design , decoupled from other layers.

Evolution

The evolution of the three-tier architecture to the DDD architecture mainly occurs in the logic layer and database access layer

• ##New DTO is added to provide higher availability and flexibility of front-end data;

• The business logic layer of the three-tier architecture is changed to the application layer and domain layer, making the business The logic is not confusing, and the application responds quickly to changes in the front end;

• The design changes of the base layer and data access layer realize the decoupling of basic resources from the basic settings through dependency inversion to cope with the changes of mainstream technologies. Variety.

Project structure

User interface layer

• Assembler: DTO and entity objects Mutual conversion and data exchange appear at the same time as DTO;

• Dto: data transmission carrier, DTO can isolate domain objects from the outside world;

• Facade: Coarse interface granularity definition, which handles requests to multiple application services;

Application layer

• event: mainly stores event-related codes. It includes two subdirectories, publish and subscribe, where publish and subscribe related codes are placed. Here you can get service subscriptions in different fields or subscriptions between microservices;

• service: application service, mainly for External services are encapsulated, orchestrated and encapsulated to provide coarse-grained services and an independent business logic

Domain layer

• Aggregate: The root directory of the aggregate software package, named according to the name of the aggregate, can define entities, aggregate roots, entities, value objects and domain services, and can be independently split into microservices;

• Entity : Stores aggregate roots, entities, value objects, factory mode related codes, and unified entity related logic, all are placed in this class, using congestion mode;

• Event: stores event entities and Logic code related to event activities;

• Service: Domain service, business logic based on different entity combinations;

• Repository: Stores aggregate queries and persistence domain object code;

Basic layer

• Config: mainly stores configuration-related code, such as springboot automatic configuration and integration Configuration of third-party components;

• Util: mainly stores basic codes such as platforms, development frameworks, messages, databases, caches, files, buses, gateways, third-party libraries, and general algorithms. You Different subdirectories can be created for different resource categories;

Sample code

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