【SpringBoot 注解】合集

参考： https://www.baeldung.com/spring-boot-annotations

@SpringBootApplication

mark the main class of a Spring Boot application:

@SpringBootApplication encapsulates @Configuration, @EnableAutoConfiguration, and @ComponentScan annotations with their default attributes.

@EnableAutoConfiguration

@EnableAutoConfiguration enables auto-configuration. It means that Spring Boot looks for auto-configuration beans on its classpath and automatically applies them.

we have to use this annotation with @Configuration:

@Configuration
@EnableAutoConfiguration
class VehicleFactoryConfig {}

Auto-Configuration Conditions

when we write our custom auto-configurations, we want Spring to use them conditionally. We can place the annotations in this section on @Configuration classes or @Bean methods.

@ConditionalOnClass and @ConditionalOnMissingClass

Using these conditions, Spring will only use the marked auto-configuration bean if the class in the annotation's argument is present/absent:

@Configuration
@ConditionalOnClass(DataSource.class)
class MySQLAutoconfiguration {
    //...
}

@ConditionalOnBean and @ConditionalOnMissingBean

@Bean
@ConditionalOnBean(name = "dataSource")
LocalContainerEntityManagerFactoryBean entityManagerFactory() {
    // ...
}

@ConditionalOnProperty

@Bean
@ConditionalOnProperty(
    name = "usemysql", 
    havingValue = "local"
)
DataSource dataSource() {
    // ...
}

@ConditionalOnResource

@ConditionalOnResource(resources = "classpath:mysql.properties")
Properties additionalProperties() {
    // ...
}

@ConditionalOnWebApplication and @ConditionalOnNotWebApplication

@ConditionalOnWebApplication
HealthCheckController healthCheckController() {
    // ...
}

@ConditionalExpression

@Bean
@ConditionalOnExpression("${usemysql} && ${mysqlserver == 'local'}")
DataSource dataSource() {
    // ...
}

@Conditional

 we can create a class evaluating the custom condition. We tell Spring to use this custom condition with @Conditional:

@Conditional(HibernateCondition.class)
Properties additionalProperties() {
    //...
}