（一）springboot原理—

（一）springboot原理——自动装配

1.spring配置方式

1.1XML方式

package com.mine.boot.version1;

public class InstA {

    public InstA() {
        System.out.println("InstA实例化");
    }

}

package com.mine.boot.version1;

public class InstB {
    public InstB() {
        System.out.println("InstB实例化");
    }
}

spring-bean.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context.xsd
    http://www.springframework.org/schema/mvc
    http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd">


    <bean id="instA" class="com.mine.boot.version1.InstA"></bean>

    <bean id="instB" class="com.mine.boot.version1.InstB"></bean>
</beans>

获取IOC容器中的Bean

    public static void main(String[] args) {
        ClassPathXmlApplicationContext classPathXmlApplicationContext = new ClassPathXmlApplicationContext("spring-bean.xml");
        InstA instA = classPathXmlApplicationContext.getBean(InstA.class);
        System.out.println(instA);
    }

运行结果：

16:35:49.334 [main] DEBUG org.springframework.beans.factory.xml.XmlBeanDefinitionReader - Loaded 2 bean definitions from class path resource [spring-bean.xml]
16:35:49.386 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'instA'
InstA实例化
16:35:49.402 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'instB'
InstB实例化
com.mine.boot.version1.InstA@33c7e1bb

1.2JavaConfig方式

package com.mine.boot.version2;

public class InstA {

    public InstA() {
        System.out.println("InstA实例化");
    }

}


package com.mine.boot.version2;

public class InstB {
    public InstB() {
        System.out.println("InstB实例化");
    }
}

package com.mine.boot.version2;

BeanConfig

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class BeanConfig {

    @Bean
    public InstA instA() {
        return new InstA();
    }

    @Bean
    public InstB instB() {
        return new InstB();
    }
}

获取IOC容器中的Bean

    public static void main(String[] args) {
        AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(BeanConfig.class);
        InstA instA = annotationConfigApplicationContext.getBean(InstA.class);
        System.out.println(instA);
    }

运行结果：

16:39:34.677 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'instA'
InstA实例化
16:39:34.693 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'instB'
InstB实例化
com.mine.boot.version2.InstA@4f638935

2.SpringBoot介绍

来自：百度百科
Spring Boot是由Pivotal团队提供的全新框架，其设计目的是用来简化新Spring应用的初始搭建以及开发过程。该框架使用了特定的方式来进行配置，从而使开发人员不再需要定义样板化的配置。通过这种方式，Spring Boot致力于在蓬勃发展的快速应用开发领域(rapid application development)成为领导者。

SpringBoot所具备的特征有：

可以创建独立的Spring应用程序，并且基于其Maven或Gradle插件，可以创建可执行的JARs和WARs；
内嵌Tomcat或Jetty等Servlet容器；
提供自动配置的“starter”项目对象模型（POMS）以简化Maven配置；
尽可能自动配置Spring容器；
提供准备好的特性，如指标、健康检查和外部化配置；
绝对没有代码生成，不需要XML配置。

自我理解：
springboot 简化了传统项目中组件依赖的配置方式如：
1.若项目中需要mcv组件，需要手动添加mvc相关的各个jar包（maven依赖或手动导入），而springboot只需要添加一个spring-boot-starter-web依赖就可以把spring核心，spring-web，spring-webmvc,tomcat容器相关的包加载进来，减少了资源包的配置过程。
2.自动配置，通过springboot定义好的配置类，完成各个组件所需要的配置基本过程，减少了整合第三方组件的配置过程，如redisTemplate。

3.springBoot自动装配

springboot启动的入口：SpringApplication.run(BootApplication.class, args)方法

@RestController
@SpringBootApplication
public class BootApplication {

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

    @RequestMapping("hi")
    public String hi() {
        return "hi boot";
    }

}

@SpringBootApplication注解：

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
		@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM,
				classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {

@SpringBootApplication注解中比较重要的有三个：

@SpringBootConfiguration：==》里面其实是@Configuration，说明BootApplication类也是一个JavaConfig配置类（等同于bean.xml）,可以在BootApplication类里面定义@Bean等配置信息。
@ComponentScan：包扫描，扫描当前类所在包，以及子包下的注解类（@Controller，@Service，@Repository，@Component）加入到IOC容器中。
@EnableAutoConfiguration：重点是@Import(AutoConfigurationImportSelector.class)自动配置导入选择，它帮我们导入AutoConfigurationImportSelector类。

springboot启动调用SpringApplication.run()方法，在run()方法中有一个refreshContext(context)方法，刷新spring的容器，在这个过程中，spring会解析当前类的@SpringBootApplication的注解，会调用AutoConfigurationImportSelector类中的selectImports(AnnotationMetadata annotationMetadata)方法，该方法下有个getCandidateConfigurations()方法（获取候选配置）

        /*
        所有的配置都存放在configurations中，
        而这些配置都从getCandidateConfiguration中获取，
        这个方法是用来获取候选的配置。
        */
	protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
			AnnotationAttributes attributes) {
		List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
				getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
		Assert.notEmpty(configurations,
				"No auto configuration classes found in META-INF/spring.factories. If you "
						+ "are using a custom packaging, make sure that file is correct.");
		return configurations;
	}

loadSpringFactories()方法加载类路径下的（FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories"）的spring.factories文件

	private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
		MultiValueMap<String, String> result = cache.get(classLoader);
		if (result != null) {
			return result;
		}

		try {
			Enumeration<URL> urls = (classLoader != null ?
					classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
			...
		}
	}

spring.factories文件下Auto Configure：也就是会获取可能依赖的组件的配置类的全路径，也不是全部XXXAutoConfiguration都会加载，也会根据@ConditionalOnXXX条件注解选择性加载配置类，加载的配置类中定义的Bean会加入到IOC容器中，从而实现自动装配。

# Auto Configure
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,
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,
org.springframework.boot.autoconfigure.cloud.CloudServiceConnectorsAutoConfiguration,
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,
org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,
org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration,
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,
org.springframework.boot.autoconfigure.reactor.core.ReactorCoreAutoConfiguration,
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,
org.springframework.boot.autoconfigure.security.servlet.SecurityRequestMatcherProviderAutoConfiguration,
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,
org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,
org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,
org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,
org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,
org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,
org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,
org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration

案例：redis自动配置
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,

@Configuration
@ConditionalOnClass(RedisOperations.class)
@EnableConfigurationProperties(RedisProperties.class)
@Import({ LettuceConnectionConfiguration.class, JedisConnectionConfiguration.class })
public class RedisAutoConfiguration {

	@Bean
	@ConditionalOnMissingBean(name = "redisTemplate")
	public RedisTemplate<Object, Object> redisTemplate(
			RedisConnectionFactory redisConnectionFactory) throws UnknownHostException {
		RedisTemplate<Object, Object> template = new RedisTemplate<>();
		template.setConnectionFactory(redisConnectionFactory);
		return template;
	}

	@Bean
	@ConditionalOnMissingBean
	public StringRedisTemplate stringRedisTemplate(
			RedisConnectionFactory redisConnectionFactory) throws UnknownHostException {
		StringRedisTemplate template = new StringRedisTemplate();
		template.setConnectionFactory(redisConnectionFactory);
		return template;
	}

}

RedisProperties:

@ConfigurationProperties(prefix = "spring.redis")
public class RedisProperties {

	/**
	 * Database index used by the connection factory.
	 */
	private int database = 0;

	/**
	 * Connection URL. Overrides host, port, and password. User is ignored. Example:
	 * redis://user:password@example.com:6379
	 */
	private String url;

	/**
	 * Redis server host.
	 */
	private String host = "localhost";

	/**
	 * Login password of the redis server.
	 */
	private String password;

	/**
	 * Redis server port.
	 */
	private int port = 6379;

	/**
	 * Whether to enable SSL support.
	 */
	private boolean ssl;

	/**
	 * Connection timeout.
	 */
	private Duration timeout;

	private Sentinel sentinel;

	private Cluster cluster;

	private final Jedis jedis = new Jedis();

	private final Lettuce lettuce = new Lettuce();

        ......

流程：

结论：
SpringBoot所有自动配置类都是在启动的时候进行扫描并加载，通过spring.factories可以找到自动配置类的路径，但是不是所有存在于spring,factories中的配置都进行加载，而是通过@ConditionalOnClass注解进行判断条件是否成立（只要导入相应的stater，条件就能成立），如果条件成立则加载配置类，否则不加载该配置类。

在这里贴一个我认为的比较容易理解的过程：

SpringBoot在启动的时候从类路径下的META-INF/spring.factories中获取EnableAutoConfiguration指定的值
将这些值作为自动配置类导入容器，自动配置类就生效，帮我们进行自动配置工作；
以前我们需要自己配置的东西，自动配置类都帮我们解决了
整个J2EE的整体解决方案和自动配置都在springboot-autoconfigure的jar包中；
它将所有需要导入的组件以全类名的方式返回，这些组件就会被添加到容器中；
它会给容器中导入非常多的自动配置类（xxxAutoConfiguration）, 就是给容器中导入这个场景需要的所有组件，并配置好这些组件；
有了自动配置类，免去了我们手动编写配置注入功能组件等的工作；

参考：https://zhuanlan.zhihu.com/p/95217578