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translated the business delegate pattern into Chinese (iluwatar#1728)
Co-authored-by: Subhrodip Mohanta <hello@subho.xyz>
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‎zh/business-delegate/README.md

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---
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layout: pattern
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title: Business Delegate
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folder: business-delegate
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permalink: /patterns/business-delegate/
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categories: Structural
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tags:
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- Decoupling
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---
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## 作用
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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。
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## 解释
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真实世界的案例
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> 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。
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简而言之
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> 业务委托模式在表现层和业务层之间增加了一个抽象层。
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维基百科的解释
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> Business delegate is a Java EE design pattern. This pattern is directing to reduce the coupling
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> in between business services and the connected presentation tier, and to hide the implementation
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> details of services (including lookup and accessibility of EJB architecture). Business delegates
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> acts as an adaptor to invoke business objects from the presentation tier.
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>
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> 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。
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**编程示例**
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首先，我们实现了一个视频流服务的抽象，和几个具体实现。
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```java
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public interface VideoStreamingService {
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void doProcessing();
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}
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@Slf4j
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public class NetflixService implements VideoStreamingService {
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@Override
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public void doProcessing() {
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LOGGER.info("NetflixService is now processing");
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}
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}
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@Slf4j
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public class YouTubeService implements VideoStreamingService {
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@Override
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public void doProcessing() {
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LOGGER.info("YouTubeService is now processing");
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}
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}
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```
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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。
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```java
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@Setter
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public class BusinessLookup {
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private NetflixService netflixService;
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private YouTubeService youTubeService;
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public VideoStreamingService getBusinessService(String movie) {
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if (movie.toLowerCase(Locale.ROOT).contains("die hard")) {
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return netflixService;
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} else {
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return youTubeService;
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}
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}
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}
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```
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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。
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```java
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@Setter
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public class BusinessDelegate {
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private BusinessLookup lookupService;
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public void playbackMovie(String movie) {
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VideoStreamingService videoStreamingService = lookupService.getBusinessService(movie);
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videoStreamingService.doProcessing();
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}
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}
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```
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移动客户端利用业务委托来调用业务层。
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```java
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public class MobileClient {
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private final BusinessDelegate businessDelegate;
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public MobileClient(BusinessDelegate businessDelegate) {
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this.businessDelegate = businessDelegate;
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}
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public void playbackMovie(String movie) {
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businessDelegate.playbackMovie(movie);
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}
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}
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```
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最后，我们展示一下这个示例完整的操作。
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```java
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public static void main(String[] args) {
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// prepare the objects
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var businessDelegate = new BusinessDelegate();
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var businessLookup = new BusinessLookup();
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businessLookup.setNetflixService(new NetflixService());
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businessLookup.setYouTubeService(new YouTubeService());
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businessDelegate.setLookupService(businessLookup);
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// create the client and use the business delegate
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var client = new MobileClient(businessDelegate);
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client.playbackMovie("Die Hard 2");
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client.playbackMovie("Maradona: The Greatest Ever");
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}
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```
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以下是终端输出的内容。
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```
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21:15:33.790 [main] INFO com.iluwatar.business.delegate.NetflixService - NetflixService is now processing
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21:15:33.794 [main] INFO com.iluwatar.business.delegate.YouTubeService - YouTubeService is now processing
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```
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## 类图
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![alt text](../../business-delegate/etc/business-delegate.urm.png "Business Delegate")
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## 相关模式
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* [Service locator pattern](https://java-design-patterns.com/patterns/service-locator/)
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## 适用场景
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业务委托模式的适用场景：
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* 你希望表现层和业务层之间是松耦合的。
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* 你想要协调对多个业务服务的调用。
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* 你想要对服务查询、服务调用进行封装。
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## 教程
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* [Business Delegate Pattern at TutorialsPoint](https://www.tutorialspoint.com/design_pattern/business_delegate_pattern.htm)
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## 鸣谢
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* [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)
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* [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)

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