SpringBoot自动配置

SpringBoot自动配置

SpringBoot自动配置

入口：

@SpringBootApplication
public class StudyApplication {

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

}

@SpringBootApplication:

@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 {
    ...
}

@EnableAutoConfiguration:

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

AutoConfigurationImportSelector:

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
    List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.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;
}

查看META-INF/spring.factories：

...
# Auto Configuration Import Filters
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
org.springframework.boot.autoconfigure.condition.OnClassCondition,\
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition

# 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,\
...

查看其中的一个类org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration：

@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnClass({RabbitTemplate.class, Channel.class})
@EnableConfigurationProperties({RabbitProperties.class})
@Import({RabbitAnnotationDrivenConfiguration.class})
public class RabbitAutoConfiguration {
    .....
}

查看RabbitProperties 即会配置相关spring.rabbitmq开头的配置：

@ConfigurationProperties(
    prefix = "spring.rabbitmq"
)
public class RabbitProperties {
    private static final int DEFAULT_PORT = 5672;
    private static final int DEFAULT_PORT_SECURE = 5671;
    private String host = "localhost";
    private Integer port;
    private String username = "guest";
    private String password = "guest";
    private final RabbitProperties.Ssl ssl = new RabbitProperties.Ssl();
    private String virtualHost;
    private String addresses;
    @DurationUnit(ChronoUnit.SECONDS)
    private Duration requestedHeartbeat;
    private int requestedChannelMax = 2047;
    private boolean publisherReturns;
    private ConfirmType publisherConfirmType;
    private Duration connectionTimeout;
    private final RabbitProperties.Cache cache = new RabbitProperties.Cache();
    private final RabbitProperties.Listener listener = new RabbitProperties.Listener();
    private final RabbitProperties.Template template = new RabbitProperties.Template();
    private List<RabbitProperties.Address> parsedAddresses;
    ....
}

条件注解

@ConditionalOnBean：当容器里有指定的bean的条件下。

@ConditionalOnMissingBean：当容器里不存在指定bean的条件下。

@ConditionalOnClass：当类路径下有指定类的条件下。

@ConditionalOnMissingClass：当类路径下不存在指定类的条件下。

@ConditionalOnProperty：指定的属性是否有指定的值，比如@ConditionalOnProperties(prefix=”xxx.xxx”, value=”enable”, matchIfMissing=true)，代表当xxx.xxx为enable时条件的布尔值为true，如果没有设置的情况下也为true。

自动配置流程

Spring Boot启动的时候会通过@EnableAutoConfiguration注解找到META-INF/spring.factories配置文件中的所有自动配置类，并对其进行加载，而这些自动配置类都是以AutoConfiguration结尾来命名的，它实际上就是一个JavaConfig形式的Spring容器配置类，它能通过以Properties结尾命名的类中取得在全局配置文件中配置的属性如：server.port，而XxxxProperties类是通过@ConfigurationProperties注解与全局配置文件中对应的属性进行绑定的。

赏

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