Spring Boot 入门 - 进阶篇（7）- 自动配置(AutoConfigure)

自动配置是Spring Boot的最大亮点，完美的展示了CoC约定由于配置。Spring Boot能自动配置Spring各种子项目（Spring MVC, Spring Security, Spring Data, Spring Cloud, Spring Integration, Spring Batch等）以及第三方开源框架所需要定义的各种Bean。 

Spring Boot内部定义了各种各样的XxxxAutoConfiguration配置类，预先定义好了各种所需的Bean。只有在特定的情况下这些配置类才会被起效。 

（1）如何导入的自动配置类  
查看源码可以看看自动配置类是如何被引入的。 

a） 应用入口 

 @SpringBootApplication
 public class SpringBootDemoApplication {

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

 }

b） 类注解 @SpringBootApplication = @EnableAutoConfiguration + @ComponentScan + @Configuration 

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

 @Configuration
 public @interface SpringBootConfiguration {
     // ...
 }

c）开启自动配置注解 @EnableAutoConfiguration 

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

d）导入配置类 EnableAutoConfigurationImportSelector extends AutoConfigurationImportSelector 

在AutoConfigurationImportSelector类中可以看到通过 SpringFactoriesLoader.loadFactoryNames() 
把 spring-boot-autoconfigure-1.5.1.RELEASE.jar/META-INF/spring.factories 下 

引用

# 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.web.WebClientAutoConfiguration,\ 
org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\ 
org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration,\ 
org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration,\ 
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration

应用启动后是如何加载这些类的呢？ 
通过执行SpringApplication.run()方法，会把当前的SpringBootDemoApplication作为source传入而在SpringApplication类中还会读取spring.factories中的设置一并构建应用的Context。 

spring-boot-1.5.1.RELEASE.jar/META-INF/spring.factories 

引用

# Application Context Initializers 
org.springframework.context.ApplicationContextInitializer=\ 
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\ 
org.springframework.boot.context.ContextIdApplicationContextInitializer,\ 
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\ 
org.springframework.boot.context.embedded.ServerPortInfoApplicationContextInitializer

spring-boot-autoconfigure-1.5.1.RELEASE.jar/META-INF/spring.factories 

引用

# Initializers 
org.springframework.context.ApplicationContextInitializer=\ 
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\ 
org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer

相应在做war时也是把当前的SpringBootDemoApplication作为source传给了ServletInitializer。 

 public class ServletInitializer extends SpringBootServletInitializer {
     @Override
     protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
         return application.sources(SpringBootDemoApplication.class);
     }
 }

配置类也可自行导入 

 @Configuration
 @Import({
         DispatcherServletAutoConfiguration.class,
         EmbeddedServletContainerAutoConfiguration.class,
         ErrorMvcAutoConfiguration.class,
         HttpEncodingAutoConfiguration.class,
         HttpMessageConvertersAutoConfiguration.class,
         JacksonAutoConfiguration.class,
         MultipartAutoConfiguration.class,
         ServerPropertiesAutoConfiguration.class,
         WebMvcAutoConfiguration.class
 })
 @ComponentScan
 public class SpringBootDemoApplication {
     public static void main(String[] args) {
         SpringApplication.run(SpringBootDemoApplication.class, args);
     }
 }

（2）自动配置类内部构成  

举例查看 org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration 

 @Configuration
 @ConditionalOnWebApplication(type = Type.SERVLET)
 @ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurerAdapter.class })
 @ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
 @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
 @AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, ValidationAutoConfiguration.class })
 public class WebMvcAutoConfiguration {

     @Bean
     @ConditionalOnMissingBean(HiddenHttpMethodFilter.class)
     public OrderedHiddenHttpMethodFilter hiddenHttpMethodFilter() {
         return new OrderedHiddenHttpMethodFilter();
     }

     // ...

 }

条件配置  基于Spring的@Conditional，SpringBoot提供了丰富的条件配置： 

引用

@ConditionalOnClass ： classpath中存在该类时起效 
@ConditionalOnMissingClass ： classpath中不存在该类时起效 
@ConditionalOnBean ： DI容器中存在该类型Bean时起效 
@ConditionalOnMissingBean ： DI容器中不存在该类型Bean时起效 
@ConditionalOnSingleCandidate ： DI容器中该类型Bean只有一个或@Primary的只有一个时起效 
@ConditionalOnExpression ： SpEL表达式结果为true时 
@ConditionalOnProperty ： 参数设置或者值一致时起效 
@ConditionalOnResource ： 指定的文件存在时起效 
@ConditionalOnJndi ： 指定的JNDI存在时起效 
@ConditionalOnJava ： 指定的Java版本存在时起效 
@ConditionalOnWebApplication ： Web应用环境下起效 
@ConditionalOnNotWebApplication ： 非Web应用环境下起效

 @Conditional({OnClassCondition.class})
 public @interface ConditionalOnClass {
     // ...
 }

 public class OnClassCondition extends SpringBootCondition implements ... {
     // ...
     // MatchType.PRESENT 判断classpath里是否存在指定类
 }

 public abstract class SpringBootCondition implements Condition {
     // ...
 }

执行顺序  

引用

@AutoConfigureAfter：在指定的配置类初始化后再加载 
@AutoConfigureBefore：在指定的配置类初始化前加载 
@AutoConfigureOrder：数越小越先初始化

（3）查看项目实际配置了什么  
运行时开启DEBUG模式后即可在控制台看到具体的自动配置结果。 

/src/main/resources/application.properties 

引用

debug=true

引用

========================= 
AUTO-CONFIGURATION REPORT 
========================= 


Positive matches: 
----------------- 

   DispatcherServletAutoConfiguration matched: 
      - @ConditionalOnClass found required class 'org.springframework.web.servlet.DispatcherServlet'; @ConditionalOnMissingClass did not find unwanted class 

(OnClassCondition) 
      - @ConditionalOnWebApplication (required) found StandardServletEnvironment (OnWebApplicationCondition) 

   DispatcherServletAutoConfiguration.DispatcherServletConfiguration matched: 
      - @ConditionalOnClass found required class 'javax.servlet.ServletRegistration'; @ConditionalOnMissingClass did not find unwanted class 

(OnClassCondition) 
      - Default DispatcherServlet did not find dispatcher servlet beans (DispatcherServletAutoConfiguration.DefaultDispatcherServletCondition) 

....... 

Negative matches: 
----------------- 

   ActiveMQAutoConfiguration: 
      Did not match: 
         - @ConditionalOnClass did not find required classes 'javax.jms.ConnectionFactory', 'org.apache.activemq.ActiveMQConnectionFactory' 

(OnClassCondition) 

   AopAutoConfiguration: 
      Did not match: 
         - @ConditionalOnClass did not find required classes 'org.aspectj.lang.annotation.Aspect', 'org.aspectj.lang.reflect.Advice' (OnClassCondition) 

....... 

Exclusions: 
----------- 

    None 


Unconditional classes: 
---------------------- 

    org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration 

    org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration 

    org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration 

    org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration

比如可以看到SpringBoot默认开启了： 

引用

DispatcherServletAutoConfiguration 注册DispatcherServlet 
EmbeddedServletContainerAutoConfiguration.EmbeddedTomcat 注册Tomcat容器 
ErrorMvcAutoConfiguration 注册异常处理器 
HttpEncodingAutoConfiguration 注册编码过滤器CharacterEncodingFilter 
HttpMessageConvertersAutoConfiguration 注册json或者xml处理器 
JacksonAutoConfiguration 注册json对象解析器 
MultipartAutoConfiguration 注册文件传输处理器 
TransactionAutoConfiguration 注册事物管理处理器 
ValidationAutoConfiguration 注册数据校验处理器 
WebMvcAutoConfiguration 注册SpringMvc相关处理器

（4）关闭自动配置  

全体无效化  

a）使用@Configuration @ComponentScan 代替 @SpringBootApplication。 

b）参数设置 
src/main/resources/application.properties 

引用

spring.boot.enableautoconfiguration=false

部分无效化 

 @SpringBootApplication(exclude=HibernateJpaAutoConfiguration.class)

或 
src/main/resources/application.properties 

引用

spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration

 @SpringBootApplication(exclude={DataSourceAutoConfiguration.class, DataSourceTransactionManagerAutoConfiguration.class, HibernateJpaAutoConfiguration.class})

或 
src/main/resources/application.properties 

引用

spring.autoconfigure.exclude[0]=org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration
spring.autoconfigure.exclude[1]=org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration
spring.autoconfigure.exclude[2]=org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration
spring.autoconfigure.exclude[3]=org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration

参考： 
http://qiita.com/kazuki43zoo/items/8645d9765edd11c6f1dd 
http://d.hatena.ne.jp/Kazuhira/20170219/1487513127