1 自定义starter的原理

• 这个场景需要使用的依赖是什么？
• 如何编写自动配置。

@Configuration  //指定这个类是配置
@ConditionalOnXxx //在指定条件成立的情况下自动配置类生成
@AutoConfigureAfter //指定自动配置类的顺序
@Bean //给容器中添加组件
@ConfigurationProperties结合相关的XxxxProperties类来绑定相关的配置
@EnableConfigurationProperties //让XxxProperties类生效，并加入到容器中    
自动配置类要能加载，需要将其配置到META-INF/spring.factories
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
...

• 启动器（starter）是一个空的jar文件，仅仅提供辅助性依赖管理，这些依赖可能用于自动装配或其他类库。

2 自定义starter

2.1 使用IDEA新建一个空的工程spring-boot-starter

2.2 新建sunxiaping-spring-boot-starter-autoconfigurer工程

• 导入相关jar的Maven坐标：

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.3.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.sunxiaping.starter</groupId>
    <artifactId>sunxiaping-spring-boot-starter-autoconfigurer</artifactId>
    <version>0.0.1</version>
    <name>sunxiaping-spring-boot-starter-autoconfigurer</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>14</java.version>
    </properties>
    <dependencies>
        <!--    引入spring-boot-starter    -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
    </dependencies>
</project>

• 新建HelloProperties.java

package com.sunxiaping.starter;
import org.springframework.boot.context.properties.ConfigurationProperties;
@ConfigurationProperties(prefix = "sunxiaping.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;
    }
}

• 新建HelloService.java

package com.sunxiaping.starter;
public class HelloService {
    private 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();
    }
}

• 新建HelloServiceAutoConfiguration.java

package com.sunxiaping.starter;
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
@EnableConfigurationProperties(value = HelloProperties.class)
public class HelloServiceAutoConfiguration {
    @Autowired
    private HelloProperties helloProperties;
    @Bean
    public HelloService helloService(){
        HelloService helloService = new HelloService();
        helloService.setHelloProperties(helloProperties);
        return helloService;
    }
}

• 在resource目录下新建META-INF目录，并在其新建spring.factories文件

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.sunxiaping.starter.HelloServiceAutoConfiguration

2.3 新建sunxiaping-spring-boot-starter工程

• 新建相关jar包的Maven坐标：

<?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.sunxiaping.starter</groupId>
    <artifactId>sunxiaping-spring-boot-starter</artifactId>
    <version>1.0</version>
    <!--  启动器  -->
    <dependencies>
        <!--   引入自动配置模块     -->
        <dependency>
            <groupId>com.sunxiaping.starter</groupId>
            <artifactId>sunxiaping-spring-boot-starter-autoconfigurer</artifactId>
            <version>0.0.1</version>
        </dependency>
    </dependencies>
</project>