Mastering Spring Boot @Conditional Annotations: A Complete Guide

Environment: SpringBoot 2.7.16

1. Introduction

Spring Boot provides many @Conditional annotations that can be applied to @Configuration classes or individual @Bean methods to control their inclusion. The main types are:

Class Conditions

Bean Conditions

Property Conditions

Resource Conditions

Web Application Conditions

SpEL Expression Conditions

2. Class Conditions

@ConditionalOnClass and @ConditionalOnMissingClass allow a configuration class to be included only when a specific class is present or absent.

<code>@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(CustomLogImpl.class)
public class PackConfiguration {
    @Bean
    public LogAspect logAspect() {
        // ...
    }
}</code>

If you use @ConditionalOnClass or @ConditionalOnMissingClass as part of a meta‑annotation, you must use the name attribute because the class reference will not be processed.

3. Bean Conditions

@ConditionalOnBean and @ConditionalOnMissingBean include a bean based on the presence or absence of another bean. You can specify the bean by type ( value ) or by name ( name ), and the search attribute controls the context hierarchy considered.

<code>@Configuration
public class PackConfiguration {
    // Only search in the current container; parent containers are ignored
    @Bean
    @ConditionalOnMissingBean(search = SearchStrategy.CURRENT)
    public UserService userService() {
        return new UserService();
    }
}</code>

Be careful with the order of bean definitions, as conditions are evaluated based on already processed beans.

Note: @ConditionalOnBean and @ConditionalOnMissingBean do not prevent the creation of the @Configuration class itself. The only difference between applying the condition at the class level versus on each @Bean method is that a mismatched class‑level condition stops the configuration class from being registered as a bean.

4. Property Conditions

@ConditionalOnProperty activates a bean when a specific Spring environment property matches. By default, any existing property that is not false matches. You can refine the check with havingValue and matchIfMissing .

<code>@Configuration
public class PropertyCondition {
    @Bean
    @ConditionalOnProperty(prefix = "pack.config", name = "enabled", havingValue = "true", matchIfMissing = true)
    public AnimalService animalService() {
        return new AnimalService();
    }
}</code>

If pack.config.enabled=true is set in the configuration file, or the property is missing, the condition evaluates to true.

5. Resource Conditions

@ConditionalOnResource includes a bean only when a given resource exists on the classpath.

<code>@Configuration
public class PropertyCondition {
    @Bean
    @ConditionalOnResource(resources = {"classpath:config.properties"})
    public AnimalService animalService() {
        return new AnimalService();
    }
}</code>

The bean is created only when config.properties is present in the classpath.

6. Web Application Conditions

Use @ConditionalOnWebApplication / @ConditionalOnNotWebApplication to configure beans based on whether the application is a web application. @ConditionalOnWarDeployment / @ConditionalOnNotWarDeployment target traditional WAR deployments.

<code>@Configuration
public class PropertyCondition {
    @Bean
    @ConditionalOnWebApplication(type = Type.REACTIVE)
    public AnimalService animalService() {
        return new AnimalService();
    }
}</code>

The bean is created only when the current environment is reactive (i.e., the project includes spring-webflux and not the servlet‑based web stack).

7. SpEL Expression Conditions

@ConditionalOnExpression activates a bean based on the result of a SpEL expression.

<code>@Configuration
public class PropertyCondition {
    @Bean
    @ConditionalOnExpression("#{'true'.equals('${pack.config.enabled}')}" )
    public AnimalService animalService() {
        return new AnimalService();
    }
}</code>

8. Custom Condition

Define a custom condition by implementing Condition and creating a meta‑annotation that uses @Conditional with the custom class.

<code>public class PackConditionProperty implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        Boolean result = context.getEnvironment().getProperty("pack.config.enabled", Boolean.class, true);
        return result;
    }
}</code>

<code>@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.TYPE})
@Conditional(PackConditionProperty.class)
public @interface PackCondition {
}</code>

Apply the custom annotation to a configuration class or bean method to enforce the condition.

That concludes the article. Hope it helps!