When to use Spring @ConfigurationCondition vs. @Condition?

Question

Spring 4 has two new annotations @Condition and @ConfigurationConditon for controlling whether a bean is added to the spring application context. The JavaDoc does not provide enough context / big picture to understand the use cases for @ConfigurationCondition.

When should @ConfigurationCondition be used vs. @Condition?

public interface ConfigurationCondition extends Condition {

    /**
     * Returns the {@link ConfigurationPhase} in which the condition should be evaluated.
     */
    ConfigurationPhase getConfigurationPhase();

    /**
     * The various configuration phases where the condition could be evaluated.
     */
    public static enum ConfigurationPhase {

        /**
         * The {@link Condition} should be evaluated as a {@code @Configuration} class is
         * being parsed.
         *
         * <p>If the condition does not match at this point the {@code @Configuration}
         * class will not be added.
         */
        PARSE_CONFIGURATION,

        /**
         * The {@link Condition} should be evaluated when adding a regular (non
         * {@code @Configuration}) bean. The condition will not prevent
         * {@code @Configuration} classes from being added.
         *
         * <p>At the time that the condition is evaluated all {@code @Configuration}s
         * will have been parsed.
         */
        REGISTER_BEAN
    }

}

Answer 1

ConfigurationCondition is a specialization of Condition for @Configuration classes.

Plain Condition is just fine for 99% of your use cases so you should consider that first. The specialization is really about determining in which phase of the processing of @Configuration classes the condition should be evaluated.

There are two phases:

• PARSE_CONFIGURATION evaluates the condition when the @Configuration-annotated class is parsed. This gives a chance to fully exclude the configuration class
• REGISTER_BEAN evaluates the condition when a bean from a configuration class is registered. This does not prevent the configuration class to be added but it allows to skip a bean definition if the condition does not match (as defined by the matches method of the Condition interface)

Spring Boot has a OnBeanCondition that basically checks during the registration phase if another bean is present. This is the core of ConditionalOnBean that basically does something when a bean is present