spring boot实战(第十三篇)自动配置原理分析

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前言

Spring Boot中引入了自动配置,让开发者利用起来更加的简便、快捷,本篇讲利用RabbitMQ的自动配置为例讲分析下Spring Boot中的自动配置原理。

在上一篇末尾讲述了Spring Boot 默认情况下会为ConnectionFactory、RabbitTemplate等bean,在前面的文章中也讲到嵌入的Tomcat默认配置为8080端口

这些都属于Spring Boot自动配置的范畴,当然其自动配置相当多。

EnableAutoConfiguration注解

在创建Application时我们使用了SpringBootApplication注解,在
spring boot实战(第九篇)Application创建源码分析
中曾有所分析,再来看下其定义:

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  1. @Target(ElementType.TYPE)
  2. @Retention(RetentionPolicy.RUNTIME)
  3. @Documented
  4. @Inherited
  5. @Configuration
  6. @EnableAutoConfiguration
  7. @ComponentScan
  8. public @interface SpringBootApplication {  
  9. Class<?**>**[] exclude() default {};
  10. }

该注解上存在元注解@EnableAutoConfiguration,这就是Spring Boot自动配置实现的核心入口;其定义为:

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  1. @Target(ElementType.TYPE)
  2. @Retention(RetentionPolicy.RUNTIME)
  3. @Documented
  4. @Inherited
  5. @Import({ EnableAutoConfigurationImportSelector.class,
  6. AutoConfigurationPackages.Registrar.class })
  7. public @interface EnableAutoConfiguration {
  8. /**
  9. * Exclude specific auto-configuration classes such that they will never be applied.
  10. * @return the classes to exclude
  11. */
  12. Class<?**>**[] exclude() default {};
  13. }

很显然能看出有一特殊的注解
@Import,该注解在spring boot实战(第十篇)Spring boot Bean加载源码分析中有讲解到,加载bean时会解析Import注解,因此需要讲目光聚集在这段代码

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  1. @Import({ EnableAutoConfigurationImportSelector.class,
  2. AutoConfigurationPackages.Registrar.class })

EnableAutoConfigurationImportSelector

来看EnableAutoConfigurationImportSelector类

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  1. public String[] selectImports(AnnotationMetadata metadata) {
  2. try {
  3. AnnotationAttributes attributes = AnnotationAttributes.fromMap(metadata
  4. .getAnnotationAttributes(EnableAutoConfiguration.class.getName(),
  5. true));
  6. Assert.notNull(attributes, “No auto-configuration attributes found. Is ”
  7. + metadata.getClassName()
  8. + ” annotated with @EnableAutoConfiguration?”);
  9. // Find all possible auto configuration classes, filtering duplicates
  10. List<**String**>factories = new ArrayList<**String**>(new LinkedHashSet<**String**>(
  11. SpringFactoriesLoader.loadFactoryNames(EnableAutoConfiguration.class,
  12. this.beanClassLoader)));
  13. // Remove those specifically disabled
  14. factories.removeAll(Arrays.asList(attributes.getStringArray(“exclude”)));
  15. // Sort
  16. factories = new AutoConfigurationSorter(this.resourceLoader)
  17. .getInPriorityOrder(factories);
  18. return factories.toArray(new String[factories.size()]);
  19. }
  20. catch (IOException ex) {
  21. throw new IllegalStateException(ex);
  22. }
  23. }

看如下代码,获取类路径下spring.factories下key为EnableAutoConfiguration全限定名对应值

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  1. SpringFactoriesLoader.loadFactoryNames(EnableAutoConfiguration.class,
  2. this.beanClassLoader))

其结果为:

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  1. # Auto Configure
  2. org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  3. org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
  4. org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
  5. org.springframework.boot.autoconfigure.MessageSourceAutoConfiguration,\
  6. org.springframework.boot.autoconfigure.PropertyPlaceholderAutoConfiguration,\
  7. org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
  8. org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\
  9. org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\
  10. org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
  11. org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
  12. org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\
  13. org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\
  14. org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\
  15. org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\
  16. org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
  17. org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\
  18. org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\
  19. org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\
  20. org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\
  21. org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
  22. org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\
  23. org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\
  24. org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\
  25. org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\
  26. org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\
  27. org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\
  28. org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\
  29. org.springframework.boot.autoconfigure.jms.hornetq.HornetQAutoConfiguration,\
  30. org.springframework.boot.autoconfigure.jta.JtaAutoConfiguration,\
  31. org.springframework.boot.autoconfigure.elasticsearch.ElasticsearchAutoConfiguration,\
  32. org.springframework.boot.autoconfigure.elasticsearch.ElasticsearchDataAutoConfiguration,\
  33. org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
  34. org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
  35. org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
  36. org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\
  37. org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\
  38. org.springframework.boot.autoconfigure.mobile.DeviceResolverAutoConfiguration,\
  39. org.springframework.boot.autoconfigure.mobile.DeviceDelegatingViewResolverAutoConfiguration,\
  40. org.springframework.boot.autoconfigure.mobile.SitePreferenceAutoConfiguration,\
  41. org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
  42. org.springframework.boot.autoconfigure.mongo.MongoDataAutoConfiguration,\
  43. org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
  44. org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
  45. org.springframework.boot.autoconfigure.reactor.ReactorAutoConfiguration,\
  46. org.springframework.boot.autoconfigure.redis.RedisAutoConfiguration,\
  47. org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration,\
  48. org.springframework.boot.autoconfigure.security.FallbackWebSecurityAutoConfiguration,\
  49. org.springframework.boot.autoconfigure.social.SocialWebAutoConfiguration,\
  50. org.springframework.boot.autoconfigure.social.FacebookAutoConfiguration,\
  51. org.springframework.boot.autoconfigure.social.LinkedInAutoConfiguration,\
  52. org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration,\
  53. org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
  54. org.springframework.boot.autoconfigure.velocity.VelocityAutoConfiguration,\
  55. org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
  56. org.springframework.boot.autoconfigure.web.DispatcherServletAutoConfiguration,\
  57. org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration,\
  58. org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,\
  59. org.springframework.boot.autoconfigure.web.GzipFilterAutoConfiguration,\
  60. org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\
  61. org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\
  62. org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\
  63. org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,\
  64. org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\
  65. org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration

以上为Spring Boot中所有的自动配置相关类;在启动过程中会解析对应类配置信息,以RabbitMQ为例,则会去解析RabbitAutoConfiguration

RabbitAutoConfiguration

首先来看RabbitAutoConfiguration类上的注解:

 

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  1. @Configuration
  2. @ConditionalOnClass({ RabbitTemplate.class, Channel.class })
  3. @EnableConfigurationProperties(RabbitProperties.class)
  4. @Import(RabbitAnnotationDrivenConfiguration.class)
  5. public class RabbitAutoConfiguration {

    • @Configuration: 应该不需要解释
    • @ConditionalOnClass:表示存在对应的Class文件时才会去解析RabbitAutoConfiguration,否则直接跳过不解析,这也是为什么在不导入RabbitMQ依赖Jar时工程能正常启动的原因
    • @EnableConfigurationProperties:表示对@ConfigurationProperties的内嵌支持,默认会将对应Class这是为bean,例如这里值为RabbitProperties.class,其定义为:

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  1. @ConfigurationProperties(prefix = “spring.rabbitmq”)
  2. public class RabbitProperties {
  3. /**
  4. * RabbitMQ host.
  5. */
  6. private String host = “localhost”;
  7. /**
  8. * RabbitMQ port.
  9. */
  10. private int port = 5672; …. //省略部分代码}

RabbitProperties提供对RabbitMQ的配置信息,其前缀为spring.rabbitmq,因此在上篇中配置的host、port等信息会配置到该类上,随后@
EnableConfigurationProperties会将RabbitProperties注册为一个bean。

  • @Import为导入配置,RabbitAnnotationDrivenConfiguration具体实现如下:

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  1. @Configuration
  2. @ConditionalOnClass(EnableRabbit.class)
  3. class RabbitAnnotationDrivenConfiguration {
  4. @Autowired(required = false)
  5. private PlatformTransactionManager transactionManager;
  6. @Bean
  7. @ConditionalOnMissingBean(name = “rabbitListenerContainerFactory”)
  8. public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory(
  9. ConnectionFactory connectionFactory) {
  10. SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
  11. factory.setConnectionFactory(connectionFactory);
  12. if (this.transactionManager != null) {
  13. factory.setTransactionManager(this.transactionManager);
  14. }
  15. return factory;
  16. }
  17. @EnableRabbit
  18. @ConditionalOnMissingBean(name = RabbitListenerConfigUtils.RABBIT_LISTENER_ANNOTATION_PROCESSOR_BEAN_NAME)
  19. protected static class EnableRabbitConfiguration {
  20. }
  21. }

这里又涉及到一个重要的注解:@ConditionalOnMissingBean,其功能为如果存在指定name的bean,则该注解标注的bean不创建,
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  1. @ConditionalOnMissingBean(name = “rabbitListenerContainerFactory”)

表示的意思为:如果存在名称为rabbitListenerContainerFactory的bean,则该部分代码直接忽略,这是Spring Boot人性化体现之一,开发者申明的bean会放在第一位,实在是太懂礼貌了~~

本篇中涉及到的注解比较多,其具体实现原理在以后有时间再具体分析。

再回到RabbitAutoConfiguration类的具体实现

首先来看:
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  1. @Configuration
  2. @ConditionalOnMissingBean(ConnectionFactory.class)
  3. protected static class RabbitConnectionFactoryCreator {
  4. @Bean
  5. public ConnectionFactory rabbitConnectionFactory(RabbitProperties config) {
  6. CachingConnectionFactory factory = new CachingConnectionFactory();
  7. String addresses = config.getAddresses();
  8. factory.setAddresses(addresses);
  9. if (config.getHost() != null) {
  10. factory.setHost(config.getHost());
  11. factory.setPort(config.getPort());
  12. }
  13. if (config.getUsername() != null) {
  14. factory.setUsername(config.getUsername());
  15. }
  16. if (config.getPassword() != null) {
  17. factory.setPassword(config.getPassword());
  18. }
  19. if (config.getVirtualHost() != null) {
  20. factory.setVirtualHost(config.getVirtualHost());
  21. }
  22. return factory;
  23. }
  24. }

创建了默认的ConnectionFactory,需要注意的时,这里的ConnectionFactory无回调的设置(解答了上篇中的疑问)

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  1. @Bean
  2. @ConditionalOnMissingBean(RabbitTemplate.class)
  3. public RabbitTemplate rabbitTemplate() {
  4. return new RabbitTemplate(this.connectionFactory);
  5. }

创建了默认的RabbitTemplate;下面创建的RabbitMessagingTemplate实现对
RabbitTemplate的包装。

在RabbitAutoConfiguration类中还剩AmqpAdmin的创建没有讲解,这部分就留到后面的文章再来讲述…

本文转自 http://blog.csdn.net/liaokailin/article/details/49559951


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