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[SpringBoot] Project Source Tree Structure

SpringBoot 應用程式開發依靠 Spring Framework Annotation 自動找尋載入各個功能元件與定義設定.

Application.java
@SpringBootApplication
public class Application {
	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}
}

Spring 的進入點就如上面這段 code @SpringBootApplication 這個 annotation 是一堆 annotation 的綜合體. 預設所有的 Controller, Model, Service 等等 Spring 相關的 annotation 只能使用在與__進入點同目錄或子目錄__下, 才能被 Spring 給掃描到.

因為 Spring 框架會自動掃描, 所以專案目錄結構反而沒有特別規定或制式結構. 而專案開發管理上, 通常有兩種方式:

By feature​

In this approach, all classes pertaining to a certain feature are placed in the same package. The structure by feature looks is shown in below example:

com
 +- gfg
     +- demo
         +- MyApplication.java
         |
         +- customer
         |   +- Customer.java
         |   +- CustomerController.java
         |   +- CustomerService.java
         |   +- CustomerRepository.java
         |
         +- order
             +- Order.java
             +- OrderController.java
             +- OrderService.java
             +- OrderRepository.java

The advantages of this structure is as follows:

  • Find a class to be modified is easy.
  • By deleting a particular sub-package, all the classes related to a certain feature can be deleted.
  • Testing and Refactoring is easy.
  • Features can be shipped separately.

By Layer​

Another way to place the classes is by layer i.e; all controllers can be placed in controllers package and services under services package and all entities under domain or model etc.

com
 +- gfg
     +- demo
         +- MyApplication.java
         |
         +- domain
         |   +- Customer.java
         |   +- Order.java
         |
         +- controllers
         |     +- OrderController.java
         |   +- CustomerController.java
         |
         +- services
         |    +- CustomerService.java
         |    +- OrderService.java
         |
         +- repositories
              +- CustomerRepository.java
              +- OrderRepository.java

Though the above structure looks feasible and easy to locate classes by a layer. It has few disadvantages when compared to Structure by Feature.

  • Features or Modules cannot be shipped separately.
  • Hard to locate a class pertaining to a certain feature.
  • Code Refactoring on a certain feature is difficult since the feature classes located in every layer.

Summary​

相對於其他框架常見會用 controller / model / middleware / ... 等來設計專案目錄結構, 在 Spring Boot 下, 若功能耦合性低, 依各功能需求來設計專案目錄結構, 似乎是更適合的方式.

See Also​