启动原理

@SpringBootApplication整合了3个注解：SpringBootConfiguration、EnableAutoConfiguration、ComponentScan

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

1. @SpringBootConfiguration：表明这是一个IOC容器的配置类，相当于说明该bean是一个spring中的xml文件。例如下面的Shiroconfig配置类也用了这个注解

   @Configuration public class ShiroConfig { @Bean public ShiroFilterFactoryBean shirFilter(SecurityManager securityManager) { }

2. @ComponentScan：指定了Spring中的指定MVC bean的扫描包和Spring的扫描包，扫描路径就是该类所在的所有包。SpringBoot的注解扫描所有的同路径下的类，@Controller类归位MVC类，其它类为Spring的类

   常规mvc配置指定包 <context:component-scan base-package="com.test.Action" /> Spring也要指定Spring的注解类的扫描路径 <context:component-scan base-package="com.test" />

3. @EnableAutoConfiguration：加载Spring常规相关的类，比如DataSource，核心功能有@import注解。类似的还有@EnableEurekaServer,则会自动import Eureka相关的bena

   @AutoConfigurationPackage @Import(EnableAutoConfigurationImportSelector.class) public @interface EnableAutoConfiguration {}

习惯优于配置的原理

SpringBoot的Main方法里面run的时候会引用到SpringFactoriesLoader里面的loadFactoryNames，会扫描spring-boot-autoconfigure.jar配置包里发现META-INF/spring.factories，然后加载许多默认的Configuration的全限定名，然后反射生成Configuration，类里面会引入默认的配置参数，从而实现习惯优于配置

	public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
		String factoryClassName = factoryClass.getName();
		try {
			Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
			List<String> result = new ArrayList<String>();
}

spring.factories 文件：

# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer
# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.autoconfigure.BackgroundPreinitializer
# Auto Configuration Import Listeners
org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\
org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener
# Auto Configuration Import Filters
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnClassCondition
# 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,\

示例

1. spring.factories中获取redisConfig的全限定名。

   org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\

2. 反射生成RedisAutoConfiguration，并且制定了已经默认填好的RedisProperties.class参数类

   @Configuration @ConditionalOnClass({ JedisConnection.class, RedisOperations.class, Jedis.class }) @EnableConfigurationProperties(RedisProperties.class) public class RedisAutoConfiguration { @Bean @ConditionalOnMissingBean(RedisConnectionFactory.class) public JedisConnectionFactory redisConnectionFactory() throws UnknownHostException { return applyProperties(createJedisConnectionFactory()); } } @ConfigurationProperties(prefix = "spring.redis") public class RedisProperties { private int database = 0; private String url; private String host = "localhost"; private String password; private int port = 6379;