SpringBoot源码分析系列之一：配置自动化

@SpringBootApplication(scanBasePackages = {"com.test"})
@MapperScan("com.test.module.mapper")
@ImportResource(locations = {"classpath:springMVC-servlet.xml"})
@ServletComponentScan
public class WebApplication extends SpringBootServletInitializer{
  static Logger logger = LoggerFactory.getLogger(WebApplication.class);
  public static void main(String[] args) {
      SpringApplication.run(WebApplication.class, args);
  }
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
    @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
    @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
  @AliasFor(annotation = EnableAutoConfiguration.class)
  Class<?>[] exclude() default {};
  @AliasFor(annotation = EnableAutoConfiguration.class)
  String[] excludeName() default {};
  @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
  String[] scanBasePackages() default {};
  @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
  Class<?>[] scanBasePackageClasses() default {};
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
  String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
  /**
   * Exclude specific auto-configuration classes such that they will never be applied.
   * @return the classes to exclude
   */
  Class<?>[] exclude() default {};
  /**
   * Exclude specific auto-configuration class names such that they will never be
   * applied.
   * @return the class names to exclude
   * @since 1.3.0
   */
  String[] excludeName() default {};
}

public class AutoConfigurationImportSelector
    implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware,
    BeanFactoryAware, EnvironmentAware, Ordered{
......
    }

  protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
      AnnotationAttributes attributes) {
    //获取  
    List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
        getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
    Assert.notEmpty(configurations,
        "No auto configuration classes found in META-INF/spring.factories. If you "
            + "are using a custom packaging, make sure that file is correct.");
    return configurations;
  }

//配置注解
@Configuration
//KafkaTemplate类在classpath目录下存在时，才会去解析KafkaAutoConfiguration自动配置类
@ConditionalOnClass(KafkaTemplate.class)
//自动注入属性,如果在application.properties配置文件中定义，则会将配置文件中key对应的value值注入到KafkaProperties中
@EnableConfigurationProperties(KafkaProperties.class)
//导入KafkaAnnotationDrivenConfiguration
@Import(KafkaAnnotationDrivenConfiguration.class)
public class KafkaAutoConfiguration {
  private final KafkaProperties properties;
  private final RecordMessageConverter messageConverter;
  public KafkaAutoConfiguration(KafkaProperties properties,
      ObjectProvider<RecordMessageConverter> messageConverter) {
    this.properties = properties;
    this.messageConverter = messageConverter.getIfUnique();
  }
  //向Spring容器注入bean
  @Bean
  //在上下文中没有KafkaTemplate时，才会实例化bean
  @ConditionalOnMissingBean(KafkaTemplate.class)
  public KafkaTemplate<?, ?> kafkaTemplate(
      ProducerFactory<Object, Object> kafkaProducerFactory,
      ProducerListener<Object, Object> kafkaProducerListener) {
    KafkaTemplate<Object, Object> kafkaTemplate = new KafkaTemplate<>(
        kafkaProducerFactory);
    if (this.messageConverter != null) {
      kafkaTemplate.setMessageConverter(this.messageConverter);
    }
    kafkaTemplate.setProducerListener(kafkaProducerListener);
    kafkaTemplate.setDefaultTopic(this.properties.getTemplate().getDefaultTopic());
    return kafkaTemplate;
  }
  @Bean
  @ConditionalOnMissingBean(ProducerListener.class)
  public ProducerListener<Object, Object> kafkaProducerListener() {
    return new LoggingProducerListener<>();
  }
  @Bean
  @ConditionalOnMissingBean(ConsumerFactory.class)
  public ConsumerFactory<?, ?> kafkaConsumerFactory() {
    return new DefaultKafkaConsumerFactory<>(
        this.properties.buildConsumerProperties());
  }
  @Bean
  @ConditionalOnMissingBean(ProducerFactory.class)
  public ProducerFactory<?, ?> kafkaProducerFactory() {
    DefaultKafkaProducerFactory<?, ?> factory = new DefaultKafkaProducerFactory<>(
        this.properties.buildProducerProperties());
    String transactionIdPrefix = this.properties.getProducer()
        .getTransactionIdPrefix();
    if (transactionIdPrefix != null) {
      factory.setTransactionIdPrefix(transactionIdPrefix);
    }
    return factory;
  }
  @Bean
  @ConditionalOnProperty(name = "spring.kafka.producer.transaction-id-prefix")
  @ConditionalOnMissingBean
  public KafkaTransactionManager<?, ?> kafkaTransactionManager(
      ProducerFactory<?, ?> producerFactory) {
    return new KafkaTransactionManager<>(producerFactory);
  }
  @Bean
  @ConditionalOnProperty(name = "spring.kafka.jaas.enabled")
  @ConditionalOnMissingBean
  public KafkaJaasLoginModuleInitializer kafkaJaasInitializer() throws IOException {
    KafkaJaasLoginModuleInitializer jaas = new KafkaJaasLoginModuleInitializer();
    Jaas jaasProperties = this.properties.getJaas();
    if (jaasProperties.getControlFlag() != null) {
      jaas.setControlFlag(jaasProperties.getControlFlag());
    }
    if (jaasProperties.getLoginModule() != null) {
      jaas.setLoginModule(jaasProperties.getLoginModule());
    }
    jaas.setOptions(jaasProperties.getOptions());
    return jaas;
  }
  @Bean
  @ConditionalOnMissingBean
  public KafkaAdmin kafkaAdmin() {
    KafkaAdmin kafkaAdmin = new KafkaAdmin(this.properties.buildAdminProperties());
    kafkaAdmin.setFatalIfBrokerNotAvailable(this.properties.getAdmin().isFailFast());
    return kafkaAdmin;
  }
}