# 手写一个Spring Boot Starter

* [官方文档](https://docs.spring.io/spring-boot/docs/current/reference/html/features.html#features.developing-auto-configuration)
* [完整代码GitHub](https://github.com/icankeep/hello-spring-boot-starter)

***

1. 创建一个maven项目 hello-spring-boot-starter
2. 添加依赖

   ```xml
   <dependency>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-autoconfigure</artifactId>
   </dependency>

   <dependency>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-configuration-processor</artifactId>
   </dependency>
   ```
3. 创建 `HelloProperties`， `HelloService`, `HelloAutoConfiguration`

   ```java
   // HelloProperties.java
   // ConfigurationProperties只有在EnableConfigurationProperties显示开启时才生效

   @ConfigurationProperties(prefix = "hello")
   public class HelloProperties {
       private String name;

       public String getName() {
           return name;
       }

       public void setName(String name) {
           this.name = name;
       }
   }
   ```

   ```java
   // HelloService的实现类 HelloServiceImpl.java

   public class HelloServiceImpl implements HelloService {

       @Resource
       private HelloProperties helloProperties;

       public String sayHello() {
           System.out.println("hello, " + helloProperties.getName());
           return "";
       }
   } 
   ```

   ```java
   // HelloAutoConfiguration.java

   @Configuration
   @ConditionalOnProperty(prefix = "hello", value = "enable", matchIfMissing = true)
   @EnableConfigurationProperties(HelloProperties.class)
   @ConditionalOnClass(HelloService.class)
   public class HelloAutoConfiguration {

       @Bean
       @ConditionalOnMissingBean(HelloService.class)
       public HelloService helloService() {
           return new HelloServiceImpl();
       }
   } 
   ```
4. 在resources目录下添加 `spring.factories`

   ```properties
   org.springframework.boot.autoconfigure.EnableAutoConfiguration=org.example.HelloAutoConfiguration
   ```
5. 整体目录结构如下，已完成基本的开发工作

   ```bash
   ├── pom.xml
   ├── src
   │   ├── main
   │   │   ├── java
   │   │   │   └── org
   │   │   │       └── example
   │   │   │           ├── HelloAutoConfiguration.java
   │   │   │           ├── HelloProperties.java
   │   │   │           └── service
   │   │   │               ├── HelloService.java
   │   │   │               └── impl
   │   │   │                   └── HelloServiceImpl.java
   │   │   └── resources
   │   │       └── META-INF
   │   │           └── spring.factories
   ```
6. mvn install 安装到本地maven仓库进行测试
7. spring-boot-web 测试模块引入依赖

   ```xml
   <dependency>
       <groupId>org.example</groupId>
       <artifactId>hello-spring-boot-starter</artifactId>
       <version>0.0.1-SNAPSHOT</version>
   </dependency>
   ```