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---
layout: pattern
title: Business Delegate
folder: business-delegate
permalink: /patterns/business-delegate/
categories: Structural
tags:
- Decoupling
---
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## 含义
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业务委托模式（译者：国内也有翻译成业务代表模式）在表现层和业务层之间增加了一个抽象层。通过使用该模式，我们获得了各层之间的松散耦合，并封装了关于如何定位、连接和与构成应用程序的业务对象进行交互的知识。
## 解释
真实世界的案例
> 一个手机应用程序承诺将现有的任何电影传输到你的手机上。它捕获了用户的搜索关键字内容，并将其传递给业务委托层。业务委托层选择最合适的视频流服务，并从该服务进行视频播放。
简而言之
> 业务委托模式在表现层和业务层之间增加了一个抽象层。
维基百科的解释
> Business delegate is a Java EE design pattern. This pattern is directing to reduce the coupling
> in between business services and the connected presentation tier, and to hide the implementation
> details of services (including lookup and accessibility of EJB architecture). Business delegates
> acts as an adaptor to invoke business objects from the presentation tier.
>
> 业务委托模式是一种 Java EE 设计模式。这种模式旨在减少业务服务和所连接的表现层之间的耦合度，并隐藏服务的实现细节（包括 EJB 架构的查询和可访问性）。业务代表作为一个适配器，从表现层调用业务对象。
**编程示例**
首先，我们实现了一个视频流服务的抽象，和几个具体实现。
```java
public interface VideoStreamingService {
void doProcessing();
}
@Slf4j
public class NetflixService implements VideoStreamingService {
@Override
public void doProcessing() {
LOGGER.info("NetflixService is now processing");
}
}
@Slf4j
public class YouTubeService implements VideoStreamingService {
@Override
public void doProcessing() {
LOGGER.info("YouTubeService is now processing");
}
}
```
接下来，我们实现一个查询服务，用于决定使用哪个视频流服务。
```java
@Setter
public class BusinessLookup {
private NetflixService netflixService;
private YouTubeService youTubeService;
public VideoStreamingService getBusinessService(String movie) {
if (movie.toLowerCase(Locale.ROOT).contains("die hard")) {
return netflixService;
} else {
return youTubeService;
}
}
}
```
业务委托层使用业务查询，将电影播放请求路由到合适的视频流服务。
```java
@Setter
public class BusinessDelegate {
private BusinessLookup lookupService;
public void playbackMovie(String movie) {
VideoStreamingService videoStreamingService = lookupService.getBusinessService(movie);
videoStreamingService.doProcessing();
}
}
```
移动客户端利用业务委托来调用业务层。
```java
public class MobileClient {
private final BusinessDelegate businessDelegate;
public MobileClient(BusinessDelegate businessDelegate) {
this.businessDelegate = businessDelegate;
}
public void playbackMovie(String movie) {
businessDelegate.playbackMovie(movie);
}
}
```
最后，我们展示一下这个示例完整的操作。
```java
public static void main(String[] args) {
// prepare the objects
var businessDelegate = new BusinessDelegate();
var businessLookup = new BusinessLookup();
businessLookup.setNetflixService(new NetflixService());
businessLookup.setYouTubeService(new YouTubeService());
businessDelegate.setLookupService(businessLookup);
// create the client and use the business delegate
var client = new MobileClient(businessDelegate);
client.playbackMovie("Die Hard 2");
client.playbackMovie("Maradona: The Greatest Ever");
}
```
以下是终端输出的内容。
```
21:15:33.790 [main] INFO com.iluwatar.business.delegate.NetflixService - NetflixService is now processing
21:15:33.794 [main] INFO com.iluwatar.business.delegate.YouTubeService - YouTubeService is now processing
```
## 类图
## 相关模式
* [Service locator pattern ](https://java-design-patterns.com/patterns/service-locator/ )
## 适用场景
业务委托模式的适用场景：
* 你希望表现层和业务层之间是松耦合的。
* 你想要协调对多个业务服务的调用。
* 你想要对服务查询、服务调用进行封装。
## 教程
* [Business Delegate Pattern at TutorialsPoint ](https://www.tutorialspoint.com/design_pattern/business_delegate_pattern.htm )
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## 引用
2021-04-29 21:17:40 +08:00
* [J2EE Design Patterns ](https://www.amazon.com/gp/product/0596004273/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596004273&linkCode=as2&tag=javadesignpat-20&linkId=48d37c67fb3d845b802fa9b619ad8f31 )
* [Core J2EE Patterns: Best Practices and Design Strategies ](https://www.amazon.com/gp/product/0130648841/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=0130648841&linkId=a0100de2b28c71ede8db1757fb2b5947 )
