浅谈springboot自动配置原理

@SpringBootApplicationpublic class MyBootApplication {  public static void main(String[] args) {    SpringApplication.run(MyBootApplication.class);  } }@SpringBootConfiguration@EnableAutoConfiguration@ComponentScanpublic @interface SpringBootApplication {  }

@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@AutoConfigurationPackage@Import({AutoConfigurationImportSelector.class})public @interface EnableAutoConfiguration {  String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";  Class<?>[] exclude() default {};  String[] excludeName() default {};}

@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@Import(AutoConfigurationPackages.Registrar.class)public @interface AutoConfigurationPackage {}

//AutoConfigurationImportSelector实现DeferredImportSelector接口，而DeferredImportSelector接口又继承了ImportSelectorpublic interface ImportSelector {  String[] selectImports(AnnotationMetadata var1);}

//AutoConfigurationImportSelector.java@Overridepublic String[] selectImports(AnnotationMetadata annotationMetadata) {  if (!isEnabled(annotationMetadata)) {    return NO_IMPORTS;  }  AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);  AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,annotationMetadata);  return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());}protected AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata,AnnotationMetadata annotationMetadata) {  if (!isEnabled(annotationMetadata)) {    return EMPTY_ENTRY;  }  AnnotationAttributes attributes = getAttributes(annotationMetadata);  List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);  configurations = removeDuplicates(configurations);  Set<String> exclusions = getExclusions(annotationMetadata, attributes);  checkExcludedClasses(configurations, exclusions);  configurations.removeAll(exclusions);  configurations = filter(configurations, autoConfigurationMetadata);  fireAutoConfigurationImportEvents(configurations, exclusions);  return new AutoConfigurationEntry(configurations, exclusions);}protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {  List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),getBeanClassLoader());  return configurations;}

public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {  String factoryClassName = factoryClass.getName();  return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());}private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {  MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);  if (result != null) {    return result;  } else {    try {      Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");      LinkedMultiValueMap result = new LinkedMultiValueMap();      while(urls.hasMoreElements()) {        URL url = (URL)urls.nextElement();        UrlResource resource = new UrlResource(url);        Properties properties = PropertiesLoaderUtils.loadProperties(resource);        Iterator var6 = properties.entrySet().iterator();        while(var6.hasNext()) {          Entry<?, ?> entry = (Entry)var6.next();          String factoryClassName = ((String)entry.getKey()).trim();          String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());          int var10 = var9.length;          for(int var11 = 0; var11 < var10; ++var11) {            String factoryName = var9[var11];            result.add(factoryClassName, factoryName.trim());          }        }      }      cache.put(classLoader, result);      return result;    } catch (IOException var13) {      throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);    }  }}

# Auto Configureorg.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,/...其他省略

@Configuration@ConditionalOnClass(RedisOperations.class) //判断当前项目有没有这个类RedisOperations.class@EnableConfigurationProperties(RedisProperties.class) //启用配置属性，这里看到了熟悉的XXXProperties@Import({ LettuceConnectionConfiguration.class, JedisConnectionConfiguration.class }) //导入这两个类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;  }} //这里则保存redis初始化时的属性@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;  private boolean ssl;}