f597fc1b07
* Fix languages * Missed change for version number * Add language field for presentation * Revert change in README for double buffer Co-authored-by: Jackie Nim <=>
116 lines
3.0 KiB
Markdown
116 lines
3.0 KiB
Markdown
---
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layout: pattern
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title: Layers
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folder: layers
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permalink: /patterns/layers/
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pumlformat: svg
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categories: Architectural
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language: en
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tags:
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- Decoupling
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---
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## Intent
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Layers is an architectural pattern where software responsibilities are divided among the different
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layers of the application.
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## Explanation
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Real world example
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> Consider a web site displaying decorated cakes for weddings and such. Instead of the web page
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> directly reaching into the database, it relies on a service to deliver this information. The
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> service then queries the data layer to assimilate the needed information.
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In plain words
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> With Layers architectural pattern different concerns reside on separate layers. View layer is
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> interested only in rendering, service layer assembles the requested data from various sources, and
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> data layer gets the bits from the data storage.
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Wikipedia says
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> In software engineering, multitier architecture (often referred to as n-tier architecture) or
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> multilayered architecture is a client–server architecture in which presentation, application
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> processing, and data management functions are physically separated.
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**Programmatic Example**
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On the data layer, we keep our cake building blocks. `Cake` consist of layers and topping.
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```java
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@Entity
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public class Cake {
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@Id
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@GeneratedValue
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private Long id;
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@OneToOne(cascade = CascadeType.REMOVE)
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private CakeTopping topping;
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@OneToMany(cascade = CascadeType.REMOVE, fetch = FetchType.EAGER)
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private Set<CakeLayer> layers;
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}
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```
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The service layer offers `CakeBakingService` for easy access to different aspects of cakes.
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```java
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public interface CakeBakingService {
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void bakeNewCake(CakeInfo cakeInfo) throws CakeBakingException;
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List<CakeInfo> getAllCakes();
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void saveNewTopping(CakeToppingInfo toppingInfo);
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List<CakeToppingInfo> getAvailableToppings();
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void saveNewLayer(CakeLayerInfo layerInfo);
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List<CakeLayerInfo> getAvailableLayers();
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}
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```
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On the top we have our `View` responsible of rendering the cakes.
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```java
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public interface View {
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void render();
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}
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@Slf4j
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public class CakeViewImpl implements View {
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private final CakeBakingService cakeBakingService;
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public CakeViewImpl(CakeBakingService cakeBakingService) {
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this.cakeBakingService = cakeBakingService;
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}
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public void render() {
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cakeBakingService.getAllCakes().forEach(cake -> LOGGER.info(cake.toString()));
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}
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}
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```
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## Class diagram
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## Applicability
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Use the Layers architecture when
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* You want clearly divide software responsibilities into different parts of the program.
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* You want to prevent a change from propagating throughout the application.
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* You want to make your application more maintainable and testable.
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## Credits
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* [Pattern Oriented Software Architecture Volume 1: A System of Patterns](https://www.amazon.com/gp/product/0471958697/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0471958697&linkCode=as2&tag=javadesignpat-20&linkId=e3f42d7a2a4cc8c619bbc0136b20dadb)
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