（2）SpringBoot学习——芋道源码

本文介绍: 内容来自芋道源码（https://www.iocoder.cn/Spring-Boot/autoconfigure/?self）

EmbeddedWebServerFactoryCustomizerAutoConfiguration 类

@Configuration // <1.1>
@ConditionalOnWebApplication // <2.1>
@EnableConfigurationProperties(ServerProperties.class) // <3.1>
public class  EmbeddedWebServerFactoryCustomizerAutoConfiguration {

	/**
	 * Nested configuration if Tomcat is being used.
	 */
	@Configuration // <1.2>
	@ConditionalOnClass({ Tomcat.class, UpgradeProtocol.class })
	public static class TomcatWebServerFactoryCustomizerConfiguration {

		@Bean
		public TomcatWebServerFactoryCustomizer tomcatWebServerFactoryCustomizer(
				Environment environment, ServerProperties serverProperties) {
			// <3.2>
			return new TomcatWebServerFactoryCustomizer(environment, serverProperties);
		}

	}

	/**
	 * Nested configuration if Jetty is being used.
	 */
	@Configuration // <1.3>
	@ConditionalOnClass({ Server.class, Loader.class, WebAppContext.class })
	public static class JettyWebServerFactoryCustomizerConfiguration {

		@Bean
		public JettyWebServerFactoryCustomizer jettyWebServerFactoryCustomizer(
				Environment environment, ServerProperties serverProperties) {
			 // <3.3>
			return new JettyWebServerFactoryCustomizer(environment, serverProperties);
		}

	}

	/**
	 * Nested configuration if Undertow is being used.
	 */
	// ... 省略 UndertowWebServerFactoryCustomizerConfiguration 代码

	/**
	 * Nested configuration if Netty is being used.
	 */
	// ... 省略 NettyWebServerFactoryCustomizerConfiguration 代码

}

① 配置类
<1.1> 处，在类上添加了 @Configuration 注解，声明这是一个配置类。因为它的目的是自动配置，所以类名以 AutoConfiguration 作为后缀。

<1.2>、<1.3> 处，分别是用于初始化 Tomcat、Jetty 相关 Bean 的配置类。

结论一：通过 @Configuration 注解的配置类，可以解决“创建哪些 Bean”的问题。

② 条件注解
<2> 处，在类上添加了 @ConditionalOnWebApplication 条件注解，表示当前配置类需要在当前项目是 Web 项目的条件下，才能生效。在 Spring Boot 项目中，会将项目类型分成 Web 项目（使用 SpringMVC 或者 WebFlux）和非 Web 项目。这样我们就很容易理解，为什么 EmbeddedWebServerFactoryCustomizerAutoConfiguration 配置类会要求在项目类型是 Web 项目，只有 Web 项目才有必要创建内嵌的 Web 服务器呀。
<2.1>、<2.2> 处，在类上添加了 @ConditionalOnClass 条件注解，表示当前配置类需要在当前项目有指定类的条件下，才能生效。

③ 配置属性
< 3.1> 处，使用 @EnableConfigurationProperties 注解，让 ServerProperties 配置属性类生效。在 Spring Boot 定义了 @ConfigurationProperties 注解，用于声明配置属性类，将指定前缀的配置项批量注入到该类中。例如 ServerProperties 代码如下：

@ConfigurationProperties(prefix = "server", ignoreUnknownFields = true)
public class ServerProperties
		implements EmbeddedServletContainerCustomizer, EnvironmentAware, Ordered {

	/**
	 * Server HTTP port.
	 */
	private Integer port;

	/**
	 * Context path of the application.
	 */
	private String contextPath;
	
	// ... 省略其它属性
	
}

@Configuration
public class DataSourceConfiguration {

    @Bean
    @Profile("DEV")
    public DataSource devDataSource() {
        // ... 单机 MySQL
    }

    @Bean
    @Profile("PROD")
    public DataSource prodDataSource() {
        // ... 集群 MySQL
    }
    
}

@Configuration
public class TestConfiguration {
    @Bean
    @Conditional(XXXCondition.class) // XXXCondition： 实现Condition 接口，提供具体的条件实现。
    public Object xxxObject() {
        return new Object();
    }
}

<?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">
    <parent>
        <artifactId>lab-47</artifactId>
        <groupId>cn.iocoder.springboot.labs</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>yunai-server-spring-boot-starter</artifactId>

    <dependencies>
        <!-- 引入 Spring Boot Starter 基础库 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
            <version>2.2.2.RELEASE</version>
        </dependency>
    </dependencies>

</project>

@ConfigurationProperties(prefix = "yunai.server")
public class YunaiServerProperties {

    /**
     * 默认端口
     */
    private static final Integer DEFAULT_PORT = 8000;

    /**
     * 端口
     */
    private Integer port = DEFAULT_PORT;

    public static Integer getDefaultPort() {
        return DEFAULT_PORT;
    }

    public Integer getPort() {
        return port;
    }

    public YunaiServerProperties setPort(Integer port) {
        this.port = port;
        return this;
    }

}

@Configuration // 声明配置类
@EnableConfigurationProperties(YunaiServerProperties.class) // 使 YunaiServerProperties 配置属性类生效
public class YunaiServerAutoConfiguration {

    private Logger logger = LoggerFactory.getLogger(YunaiServerAutoConfiguration.class);

    @Bean // 声明创建 Bean
    @ConditionalOnClass(HttpServer.class) // 需要项目中存在 com.sun.net.httpserver.HttpServer 类。该类为 JDK 自带，所以一定成立。
    public HttpServer httpServer(YunaiServerProperties serverProperties) throws IOException {
        // 创建 HttpServer 对象，并启动
        HttpServer server = HttpServer.create(new InetSocketAddress(serverProperties.getPort()), 0);
        server.start();
        logger.info("[httpServer][启动服务器成功，端口为:{}]", serverProperties.getPort());

        // 返回
        return server;
    }
}

rg.springframework.boot.autoconfigure.EnableAutoConfiguration=
cn.iocoder.springboot.lab47.yunaiserver.autoconfigure.YunaiServerAutoConfiguration

<?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">
    <parent>
        <artifactId>lab-47</artifactId>
        <groupId>cn.iocoder.springboot.labs</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>lab-47-demo</artifactId>

    <dependencies>
        <!-- 引入自定义 Starter -->
        <dependency>
            <groupId>cn.iocoder.springboot.labs</groupId>
            <artifactId>yunai-server-spring-boot-starter</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
    </dependencies>

</project>

yunai:
  server:
    port: 8888 # 自定义 HttpServer 端口

@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

2020-02-02 13:03:12.156  INFO 76469 --- [           main] c.i.s.lab47.demo.DemoApplication         : Starting DemoApplication on MacBook-Pro-8 with PID 76469 (/Users/yunai/Java/SpringBoot-Labs/lab-47/lab-47-demo/target/classes started by yunai in /Users/yunai/Java/SpringBoot-Labs)
2020-02-02 13:03:12.158  INFO 76469 --- [           main] c.i.s.lab47.demo.DemoApplication         : No active profile set, falling back to default profiles: default
2020-02-02 13:03:12.873  INFO 76469 --- [           main] c.i.s.l.y.a.YunaiServerAutoConfiguration : [httpServer][启动服务器成功，端口为:8888]
2020-02-02 13:03:12.927  INFO 76469 --- [           main] c.i.s.lab47.demo.DemoApplication         : Started DemoApplication in 1.053 seconds (JVM running for 1.47)