Mike Liu
c5a4068e84
* add state and callback pattern * add command and template-method pattern * add iterator pattern * add bridege and DI pattern * fix issue #1600 * add converter,proxy,visitor pattern * add caching,composite,delegation,dirty-flag,interpreter patterns * add dao and producer-consumer * add dto and provate class data pattern * fix #1646 png path problems * fix #1646 composite png path case problem * add abstract document pattern and version-number pattern * add ambassador pattern * add acyclic-visitor and api-gateway pattern * add abstract-factory pattern * add active-object pattern * add aggregator-microservices and arrange-act-assert pattern * update async-method-invocation pattern * add balking and business-delegate pattern * add bytecode and circuit-break pattern * update arrange/act/assert pattern problems * add csch pattern * add language code, correct pic path * #1805 update permalink Co-authored-by: Subhrodip Mohanta <subhrodipmohanta@gmail.com> Co-authored-by: Mike <admin@xiaod.info> Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com>
157 lines
4.5 KiB
Markdown
157 lines
4.5 KiB
Markdown
---
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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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language: zh
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tags:
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- Decoupling
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---
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## 意图
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业务委托模式在表示层和业务层之间添加了一个抽象层。 通过使用该模式，我们获得了各层之间的松散耦合，并封装了有关如何定位，连接到组成应用程序的业务对象以及与之交互的逻辑。
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## 解释
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真实世界例子
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> 手机应用程序承诺将现有的任何电影流式传输到您的手机。它捕获用户的搜索字符串，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，然后从那里播放视频。
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通俗的说
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> 业务委托模式在表示层和业务层之间添加了一个抽象层。
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维基百科说
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> 业务委托是一种Java EE设计模式。 该模式旨在减少业务服务与连接的表示层之间的耦合，并隐藏服务的实现细节（包括EJB体系结构的查找和可访问性）。 业务代表充当适配器，以从表示层调用业务对象。
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**程序示例**
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首先，我们有视频流服务的抽象类和一些它的实现。
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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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然后我们有一个查找服务来决定我们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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业务委托类使用业务查找服务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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最后我们展示完整示例。
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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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这是控制台的输出。
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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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## 相关模式
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* [服务定位器模式](https://java-design-patterns.com/patterns/service-locator/)
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## 适用性
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使用业务委托模式当
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* 你希望表示层和业务层之间的松散耦合
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* 你想编排对多个业务服务的调用
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* 你希望封装查找服务和服务调用
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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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