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## 一、簡介
SpringBoot 最強大的功能就是把我們常用的場景抽取成了一個個starter（場景啟動器），我們透過引入springboot 為我提供的這些場景啟動器，我們再進行少量的配置就能使用相應的功能。即使是這樣，springboot也不能囊括我們所有的使用場景，往往我們需要自定義starter，來簡化我們對springboot的使用。
## 二、如何自定義starter
### 1.例項
#### 如何編寫自動配置 ？
我們參照@WebMvcAutoConfiguration為例，我們看看們需要準備哪些東西，下面是WebMvcAutoConfiguration的部分程式碼：

```java
@Configuration
@ConditionalOnWebApplication
@ConditionalOnClass({Servlet.class, DispatcherServlet.class, WebMvcConfigurerAdapter.class})
@ConditionalOnMissingBean({WebMvcConfigurationSupport.class})
@AutoConfigureOrder(-2147483638)
@AutoConfigureAfter({DispatcherServletAutoConfiguration.class, ValidationAutoConfiguration.class})
public class WebMvcAutoConfiguration {

@Import({WebMvcAutoConfiguration.EnableWebMvcConfiguration.class})
    @EnableConfigurationProperties({WebMvcProperties.class, ResourceProperties.class})
    public static class WebMvcAutoConfigurationAdapter extends WebMvcConfigurerAdapter {

@Bean
        @ConditionalOnBean({View.class})
        @ConditionalOnMissingBean
        public BeanNameViewResolver beanNameViewResolver() {
            BeanNameViewResolver resolver = new BeanNameViewResolver();
            resolver.setOrder(2147483637);
            return resolver;
        }
    }
}
```

我們可以抽取到我們自定義starter時同樣需要的一些配置。

```java
@Configuration  //指定這個類是一個配置類
@ConditionalOnXXX  //指定條件成立的情況下自動配置類生效
@AutoConfigureOrder  //指定自動配置類的順序
@Bean  //向容器中新增元件
@ConfigurationProperties  //結合相關xxxProperties來繫結相關的配置
@EnableConfigurationProperties  //讓xxxProperties生效加入到容器中

自動配置類要能載入需要將自動配置類，配置在META-INF/spring.factories中
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
```

#### 模式
我們參照 **spring-boot-starter** 我們發現其中沒有程式碼：

![](http://img.blog.itpub.net/blog/2019/05/30/06ceb7f9a128d65f.png?x-oss-process=style/bb)

我們在看它的pom中的依賴中有個 **springboot-starter**
 
```xml
<dependency>
	<groupid>org.springframework.boot</groupid>
	<artifactid>spring-boot-starter</artifactid>
</dependency>
```
我們再看看 **spring-boot-starter** 有個 **spring-boot-autoconfigure**

```xml
<dependency>
	<groupid>org.springframework.boot</groupid>
	<artifactid>spring-boot-autoconfigure</artifactid>
</dependency>
```
關於web的一些自動配置都寫在了這裡 ，所以我們有總結：

```
啟動器starter只是用來做依賴管理
需要專門寫一個類似spring-boot-autoconfigure的配置模組
用的時候只需要引入啟動器starter，就可以使用自動配置了
```

#### 命名規範
**官方名稱空間**

- 字首：spring-boot-starter-
- 模式：spring-boot-starter-模組名
- 舉例：spring-boot-starter-web、spring-boot-starter-jdbc

**自定義名稱空間**

- 字尾：-spring-boot-starter
- 模式：模組-spring-boot-starter
- 舉例：mybatis-spring-boot-starter

## 三、自定義starter例項
我們需要先建立兩個工程 **hello-spring-boot-starter** 和 **hello-spring-boot-starter-autoconfigurer**

### 1. hello-spring-boot-starter
#### 1.pom.xml
```xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelversion>4.0.0</modelversion>

<groupid>com.gf</groupid>
	<artifactid>hello-spring-boot-starter</artifactid>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

<name>hello-spring-boot-starter</name>

<dependencies>
		
		<dependency>
			<groupid>com.gf</groupid>
			<artifactid>hello-spring-boot-starter-autoconfigurer</artifactid>
			<version>0.0.1-SNAPSHOT</version>
		</dependency>
	</dependencies>

</project>

```
同時刪除 啟動類、resources下的檔案，test檔案。

### 2. hello-spring-boot-starter-autoconfigurer
#### 1. pom.xml
```xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelversion>4.0.0</modelversion>

<groupid>com.gf</groupid>
	<artifactid>hello-spring-boot-starter-autoconfigurer</artifactid>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

<name>hello-spring-boot-starter-autoconfigurer</name>
	<description>Demo project for Spring Boot</description>

<parent>
		<groupid>org.springframework.boot</groupid>
		<artifactid>spring-boot-starter-parent</artifactid>
		<version>1.5.9.RELEASE</version>
		<relativepath></relativepath> 
	</parent>

<dependencies>
		
		<dependency>
			<groupid>org.springframework.boot</groupid>
			<artifactid>spring-boot-starter</artifactid>
		</dependency>

</dependencies>

</project>

```

#### 2. HelloProperties
```java
package com.gf.service;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties(prefix = "gf.hello")
public class HelloProperties {

private String prefix;
    private String suffix;

public String getPrefix() {
        return prefix;
    }

public void setPrefix(String prefix) {
        this.prefix = prefix;
    }

public String getSuffix() {
        return suffix;
    }

public void setSuffix(String suffix) {
        this.suffix = suffix;
    }

}

```

#### 3. HelloService
```java
package com.gf.service;

public class HelloService {

HelloProperties helloProperties;

public HelloProperties getHelloProperties() {
        return helloProperties;
    }

public void setHelloProperties(HelloProperties helloProperties) {
        this.helloProperties = helloProperties;
    }

public String sayHello(String name ) {
        return helloProperties.getPrefix()+ "-" + name + helloProperties.getSuffix();
    }
}

```

#### 4. HelloServiceAutoConfiguration
```java
package com.gf.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@ConditionalOnWebApplication //web應該生效
@EnableConfigurationProperties(HelloProperties.class)
public class HelloServiceAutoConfiguration {

@Autowired
    HelloProperties helloProperties;

@Bean
    public HelloService helloService() {
        HelloService service = new HelloService();
        service.setHelloProperties( helloProperties  );
        return service;
    }

}

```
 
#### 5. spring.factories
在 **resources** 下建立資料夾 **META-INF** 並在 **META-INF** 下建立檔案 **spring.factories** ，內容如下：

```
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.gf.service.HelloServiceAutoConfiguration
```

到這兒，我們的配置自定義的starter就寫完了 ，我們hello-spring-boot-starter-autoconfigurer、hello-spring-boot-starter 安裝成本地jar包。

## 三、測試自定義starter
我們建立個專案 **hello-spring-boot-starter-test**，來測試系我們寫的stater。
### 1. pom.xml
```xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelversion>4.0.0</modelversion>

<groupid>com.gf</groupid>
	<artifactid>hello-spring-boot-starter-test</artifactid>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

<name>hello-spring-boot-starter-test</name>
	<description>Demo project for Spring Boot</description>

<parent>
		<groupid>org.springframework.boot</groupid>
		<artifactid>spring-boot-starter-parent</artifactid>
		<version>1.5.9.RELEASE</version>
		<relativepath></relativepath> 
	</parent>

<dependencies>
		<dependency>
			<groupid>org.springframework.boot</groupid>
			<artifactid>spring-boot-starter-web</artifactid>
		</dependency>

<dependency>
			<groupid>com.gf</groupid>
			<artifactid>hello-spring-boot-starter</artifactid>
			<version>0.0.1-SNAPSHOT</version>
		</dependency>

<dependency>
			<groupid>org.springframework.boot</groupid>
			<artifactid>spring-boot-starter-test</artifactid>
			<scope>test</scope>
		</dependency>
	</dependencies>

<build>
		<plugins>
			<plugin>
				<groupid>org.springframework.boot</groupid>
				<artifactid>spring-boot-maven-plugin</artifactid>
			</plugin>
		</plugins>
	</build>

</project>

```

### 2. HelloController
```java
package com.gf.controller;

import com.gf.service.HelloService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

@Autowired
    HelloService helloService;

@GetMapping("/hello/{name}")
    public String hello(@PathVariable(value = "name") String name) {
        return helloService.sayHello( name + " , " );
    }

}

```

### 3. application.properties
```
gf.hello.prefix = hi
gf.hello.suffix = what's up man ?
```
我執行專案訪問 http://127.0.0.1:8080/hello/zhangsan，結果如下：

```
hi-zhangsan , what's up man ? 
```

原始碼下載: [https://github.com/gf-huanchupk/SpringBootLearning](https://github.com/gf-huanchupk/SpringBootLearning)

Spring Boot 自定義 starter

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