Spring Boot启动原理解析（注解篇）

SpringBoot内置的自动配置使开发变得很方便，所以这次就来看看它的启动源码和它的自动化配置的实现原理。

    启动类：

1. @SpringBootApplication

2. public class DemoApplication {

3.  

4. public static void main(String[] args) {

5. SpringApplication.run(DemoApplication.class, args);

6. }

7. }

    可以看到这个启动类中有两部分：@SpringBootApplication和SpringApplication.run(DemoApplication.class, args)两部分。每个Spring Boot项目都包含这两部分。

@SpringBootApplication

1. @Target(ElementType.TYPE) // 注解的适用范围，TYPE用于描述类、接口、enum声明

2. @Retention(RetentionPolicy.RUNTIME) // 注解的生命周期

3. @Documented // 表明这个注解应该被javadoc记录

4. @Inherited // 子类可以继承该注解

5. @SpringBootConfiguration // 继承了Configuration，表示当前是注解类

6. @EnableAutoConfiguration // 开启SpringBoot的注解功能，借助@import的帮助

7. @ComponentScan(excludeFilters = { // 包扫描路径设置

8. @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),

9. @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })

10. public @interface SpringBootApplication {

11. ……

12. }

这块最重要的三个注解是：

• @Configuration：IoC容器的配置类（@SpringBootConfiguration内部有@Configuration）
• @EnableAutoConfiguration：借助@Import的支持，将所有符合自动配置条件的bean定义加载到IoC容器。
• @ComponentScan：自动扫描并加载符合条件的组件或者bean，最终将这些bean加载到IoC容器中

 这里主要研究下@EnableAutoConfiguration注解：

1. @Target(ElementType.TYPE)

2. @Retention(RetentionPolicy.RUNTIME)

3. @Documented

4. @Inherited

5. @AutoConfigurationPackage

6. @Import(AutoConfigurationImportSelector.class)

7. public @interface EnableAutoConfiguration {

8.  

9. String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

10.  

11. ……

12.  

13. }

这个注解主要有两个注解组成：

• @AutoConfigurationPackage：返回了当前主程序类的同级以及子级的包组件。
• @Import(AutoConfigurationImportSelector.class)：导入自动配置的组件

 先来看看@AutoConfigurationPackage的实现：

1. @Target(ElementType.TYPE)

2. @Retention(RetentionPolicy.RUNTIME)

3. @Documented

4. @Inherited

5. @Import(AutoConfigurationPackages.Registrar.class)

6. public @interface AutoConfigurationPackage {

7.  

8. }

9.  
10.  

11. static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {

12.  

13. @Override

14. public void registerBeanDefinitions(AnnotationMetadata metadata,

15. BeanDefinitionRegistry registry) {

16. register(registry, new PackageImport(metadata).getPackageName());

17. }

18.  

19. @Override

20. public Set<Object> determineImports(AnnotationMetadata metadata) {

21. return Collections.singleton(new PackageImport(metadata));

22. }

23.  

24. }

    它其实是注册了一个Bean的定义。new PackageImport(metadata).getPackageName()，它会返回当前主程序类的同级以及子级的包组件。

   这就是为什么要把主程序放在项目的顶层节点的原因。

下面再来看看@Import(AutoConfigurationImportSelector.class)的作用：

1. public String[] selectImports(AnnotationMetadata annotationMetadata) {

2. if (!isEnabled(annotationMetadata)) {

3. return NO_IMPORTS;

4. }

5. AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader

6. .loadMetadata(this.beanClassLoader);

7. AnnotationAttributes attributes = getAttributes(annotationMetadata);

8. List<String> configurations = getCandidateConfigurations(annotationMetadata,

9. attributes);

10. configurations = removeDuplicates(configurations);

11. Set<String> exclusions = getExclusions(annotationMetadata, attributes);

12. checkExcludedClasses(configurations, exclusions);

13. configurations.removeAll(exclusions);

14. configurations = filter(configurations, autoConfigurationMetadata);

15. fireAutoConfigurationImportEvents(configurations, exclusions);

16. return StringUtils.toStringArray(configurations);

17. }

18.  
19.  
20.  

21. protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,

22. AnnotationAttributes attributes) {

23. List<String> configurations = SpringFactoriesLoader.loadFactoryNames(

24. getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());

25. Assert.notEmpty(configurations,

26. "No auto configuration classes found in META-INF/spring.factories. If you "

27. + "are using a custom packaging, make sure that file is correct.");

28. return configurations;

29. }

30.  
31.  
32.  

33. public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {

34. String factoryClassName = factoryClass.getName();

35. return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());

36. }

37.  
38.  
39.  

40. private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {

41. MultiValueMap<String, String> result = cache.get(classLoader);

42. if (result != null) {

43. return result;

44. }

45.  

46. try {

47. Enumeration<URL> urls = (classLoader != null ?

48. classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :

49. ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));

50. result = new LinkedMultiValueMap<>();

51. while (urls.hasMoreElements()) {

52. URL url = urls.nextElement();

53. UrlResource resource = new UrlResource(url);

54. Properties properties = PropertiesLoaderUtils.loadProperties(resource);

55. for (Map.Entry<?, ?> entry : properties.entrySet()) {

56. List<String> factoryClassNames = Arrays.asList(

57. StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));

58. result.addAll((String) entry.getKey(), factoryClassNames);

59. }

60. }

61. cache.put(classLoader, result);

62. return result;

63. }

64. catch (IOException ex) {

65. throw new IllegalArgumentException("Unable to load factories from location [" +

66. FACTORIES_RESOURCE_LOCATION + "]", ex);

67. }

68. }

 

    可以看到它会从spring-boot-autoconfigure/2.0.2.RELEASE/spring-boot-autoconfigure-2.0.2.RELEASE.jar!/META-INF/spring.factories中去获取自动配置类，然后根据反射将其实例化为JavaConfig形式的IoC容器配置类，然后将其加载到IoC容器中。

1. org.springframework.boot.autoconfigure.EnableAutoConfiguration=\

2. org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\

3. org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\

4. org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\

5. org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\

6. org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\

7. org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\

8. org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\

9. org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\

10. org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\

11. org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\

12. org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\

13. org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\

14. org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\

15. org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\

16. org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\

17. org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\

18. org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\

19. org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\

20. org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\

21. org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\

22. org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\

23. org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\

24. org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\

25. org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\

26. org.springframework.boot.autoconfigure.data.ldap.LdapDataAutoConfiguration,\

27. org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\

28. org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\

29. org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\

30. org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\

31. org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\

32. org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\

33. org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\

34. org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\

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

36. org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\

37. org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\

38. org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\

39. org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\

40. org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\

41. org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\

42. org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\

43. org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\

44. org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\

45. org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\

46. org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\

47. org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\

48. org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\

49. org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\

50. org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\

51. org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\

52. org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\

53. org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\

54. org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\

55. org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\

56. org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\

57. org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\

58. org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\

59. org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\

60. org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\

61. org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\

62. org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\

63. org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\

64. org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\

65. org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\

66. org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\

67. org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\

68. org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\

69. org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\

70. org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\

71. org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\

72. org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\

73. org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\

74. org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\

75. org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\

76. org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\

77. org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\

78. org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\

79. org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\

80. org.springframework.boot.autoconfigure.reactor.core.ReactorCoreAutoConfiguration,\

81. org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\

82. org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\

83. org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\

84. org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\

85. org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\

86. org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\

87. org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\

88. org.springframework.boot.autoconfigure.security.oauth2.client.OAuth2ClientAutoConfiguration,\

89. org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\

90. org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\

91. org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\

92. org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\

93. org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\

94. org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\

95. org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\

96. org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\

97. org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\

98. org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\

99. org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\

100. org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\

101. org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\

102. org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\

103. org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\

104. org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\

105. org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\

106. org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\

107. org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\

108. org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\

109. org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\

110. org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration

执行流程篇：https://blog.youkuaiyun.com/qq_37598011/article/details/90969634