These annotations allow beans to be created only if certain conditions are met.
Here’s a breakdown with examples:
1. Using @Conditional
You can define your own condition by implementing Condition.
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;
class MyCondition implements Condition {
@Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
// Example: Register bean only if "my.feature.enabled" is true
String enabled = context.getEnvironment().getProperty("my.feature.enabled");
return "true".equalsIgnoreCase(enabled);
}
}
@Configuration
public class MyConfig {
@Bean
@Conditional(MyCondition.class)
public String conditionalBean() {
return "Bean is loaded!";
}
}
✅ If my.feature.enabled=true is in application.properties, the bean will be created.
2. @ConditionalOnProperty
Registers a bean if a property has a specific value.
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class PropertyBasedConfig {
@Bean
@ConditionalOnProperty(name = "featureX.enabled", havingValue = "true", matchIfMissing = false)
public String featureXBean() {
return "Feature X Bean loaded";
}
}
- If
featureX.enabled=true→ Bean is created. - If property missing or
false→ Bean is skipped.
3. @ConditionalOnClass
Registers a bean only if a class is on the classpath.
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class ClassBasedConfig {
@Bean
@ConditionalOnClass(name = "com.mysql.cj.jdbc.Driver")
public String mysqlBean() {
return "MySQL Bean loaded";
}
}
✅ Bean loads only if MySQL JDBC driver is present in classpath.
4. @ConditionalOnMissingBean
Registers a bean only if another bean is not already defined.
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class MissingBeanConfig {
@Bean
@ConditionalOnMissingBean(name = "customBean")
public String defaultBean() {
return "Default Bean";
}
}
✅ This prevents overriding user-defined beans unless missing.
5. @ConditionalOnExpression
Registers a bean based on a SpEL (Spring Expression Language) condition.
import org.springframework.boot.autoconfigure.condition.ConditionalOnExpression;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class ExpressionConfig {
@Bean
@ConditionalOnExpression("'${app.mode}'=='dev'")
public String devBean() {
return "Dev Mode Bean";
}
}
✅ If app.mode=dev in properties → Bean is created.
Summary Table
| Annotation | Condition |
|---|---|
@Conditional | Custom logic |
@ConditionalOnProperty | Property exists with value |
@ConditionalOnClass | Class available on classpath |
@ConditionalOnMissingBean | No existing bean of type/name |
@ConditionalOnExpression | SpEL evaluates true |