102 lines
3.2 KiB
Markdown
102 lines
3.2 KiB
Markdown
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---
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layout: pattern
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title: Dependency Injection
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folder: dependency-injection
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permalink: /patterns/dependency-injection/
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categories: Creational
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tags:
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- Decoupling
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---
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## 目的
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依赖注入是一种软件设计模式，其中一个或多个依赖项（或服务）被注入或通过引用传递到一个依赖对象（或客户端）中，并成为客户端状态的一部分。该模式将客户的依赖关系的创建与其自身的行为分开，这使程序设计可以松散耦合，并遵循控制反转和单一职责原则。
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## 解释
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真实世界例子
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> 老巫师喜欢不时地装满烟斗抽烟。 但是，他不想只依赖一个烟草品牌，而是希望能够互换使用它们。
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通俗的说
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> 依赖注入将客户端依赖的创建与其自身行为分开。
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维基百科说
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> 在软件工程中，依赖注入是一种对象接收其依赖的其他对象的技术。 这些其他对象称为依赖项。
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**程序示例**
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先介绍一下烟草接口和具体的品牌。
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```java
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public abstract class Tobacco {
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private static final Logger LOGGER = LoggerFactory.getLogger(Tobacco.class);
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public void smoke(Wizard wizard) {
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LOGGER.info("{} smoking {}", wizard.getClass().getSimpleName(),
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this.getClass().getSimpleName());
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}
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}
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public class SecondBreakfastTobacco extends Tobacco {
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}
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public class RivendellTobacco extends Tobacco {
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}
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public class OldTobyTobacco extends Tobacco {
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}
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```
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下面是老巫师的类的层次结构。
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```java
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public interface Wizard {
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void smoke();
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}
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public class AdvancedWizard implements Wizard {
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private final Tobacco tobacco;
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public AdvancedWizard(Tobacco tobacco) {
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this.tobacco = tobacco;
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}
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@Override
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public void smoke() {
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tobacco.smoke(this);
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}
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}
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```
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最后我们可以看到给老巫师任意品牌的烟草是多么的简单。
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```java
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var advancedWizard = new AdvancedWizard(new SecondBreakfastTobacco());
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advancedWizard.smoke();
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```
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## 类图
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## 适用性
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使用依赖注入当：
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- 当你需要从对象中移除掉具体的实现内容时
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* 使用模拟对象或存根隔离地启用类的单元测试
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## 鸣谢
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* [Dependency Injection Principles, Practices, and Patterns](https://www.amazon.com/gp/product/161729473X/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=161729473X&linkId=57079257a5c7d33755493802f3b884bd)
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* [Clean Code: A Handbook of Agile Software Craftsmanship](https://www.amazon.com/gp/product/0132350882/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0132350882&linkCode=as2&tag=javadesignpat-20&linkId=2c390d89cc9e61c01b9e7005c7842871)
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* [Java 9 Dependency Injection: Write loosely coupled code with Spring 5 and Guice](https://www.amazon.com/gp/product/1788296257/ref=as_li_tl?ie=UTF8&tag=javadesignpat-20&camp=1789&creative=9325&linkCode=as2&creativeASIN=1788296257&linkId=4e9137a3bf722a8b5b156cce1eec0fc1)
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* [Google Guice Tutorial: Open source Java based dependency injection framework](https://www.amazon.com/gp/product/B083P7DZ8M/ref=as_li_tl?ie=UTF8&tag=javadesignpat-20&camp=1789&creative=9325&linkCode=as2&creativeASIN=B083P7DZ8M&linkId=04f0f902c877921e45215b624a124bfe)
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