spring Conditional bean registration in Spring Condition annotations

Example

Except main @conditional annotation there are set of similar annotation to be used for different cases.

Class conditions

The @ConditionalOnClass and @ConditionalOnMissingClass annotations allows configuration to be included based on the presence or absence of specific classes.

E.g. when OObjectDatabaseTx.class is added to dependencies and there is no OrientWebConfigurer bean we create the configurer.

@Bean
@ConditionalOnWebApplication
@ConditionalOnClass(OObjectDatabaseTx.class)
@ConditionalOnMissingBean(OrientWebConfigurer.class)
public OrientWebConfigurer orientWebConfigurer() {
    return new OrientWebConfigurer();
}

Bean conditions

The @ConditionalOnBean and @ConditionalOnMissingBean annotations allow a bean to be included based on the presence or absence of specific beans. You can use the value attribute to specify beans by type, or name to specify beans by name. The search attribute allows you to limit the ApplicationContext hierarchy that should be considered when searching for beans.

See the example above when we check whether there is no defined bean.

Property conditions

The @ConditionalOnProperty annotation allows configuration to be included based on a Spring Environment property. Use the prefix and name attributes to specify the property that should be checked. By default any property that exists and is not equal to false will be matched. You can also create more advanced checks using the havingValue and matchIfMissing attributes.

@ConditionalOnProperty(value='somebean.enabled', matchIfMissing = true, havingValue="yes")
@Bean 
public SomeBean someBean(){
}

Resource conditions

The @ConditionalOnResource annotation allows configuration to be included only when a specific resource is present.

@ConditionalOnResource(resources = "classpath:init-db.sql") 

Web application conditions

The @ConditionalOnWebApplication and @ConditionalOnNotWebApplication annotations allow configuration to be included depending on whether the application is a 'web application'.

@Configuration
@ConditionalOnWebApplication
public class MyWebMvcAutoConfiguration {...}

SpEL expression conditions

The @ConditionalOnExpression annotation allows configuration to be included based on the result of a SpEL expression.

@ConditionalOnExpression("${rest.security.enabled}==false")