org.springframework.boot.autoconfigure.condition.ConditionalOnClass Maven / Gradle / Ivy
/*
* Copyright 2012-2022 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.boot.autoconfigure.condition;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Conditional;
/**
* {@link Conditional @Conditional} that only matches when the specified classes are on
* the classpath.
*
* A {@code Class} {@link #value() value} can be safely specified on
* {@code @Configuration} classes as the annotation metadata is parsed by using ASM before
* the class is loaded. If a class reference cannot be used then a {@link #name() name}
* {@code String} attribute can be used.
*
* Note: Extra care must be taken when using {@code @ConditionalOnClass} on
* {@code @Bean} methods where typically the return type is the target of the condition.
* Before the condition on the method applies, the JVM will have loaded the class and
* potentially processed method references which will fail if the class is not present. To
* handle this scenario, a separate {@code @Configuration} class should be used to isolate
* the condition. For example:
* @AutoConfiguration
* public class MyAutoConfiguration {
*
* @Configuration(proxyBeanMethods = false)
* @ConditionalOnClass(SomeService.class)
* public static class SomeServiceConfiguration {
*
* @Bean
* @ConditionalOnMissingBean
* public SomeService someService() {
* return new SomeService();
* }
*
* }
*
* }
*
* @author Phillip Webb
* @since 1.0.0
*/
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnClassCondition.class)
public @interface ConditionalOnClass {
/**
* The classes that must be present. Since this annotation is parsed by loading class
* bytecode, it is safe to specify classes here that may ultimately not be on the
* classpath, only if this annotation is directly on the affected component and
* not if this annotation is used as a composed, meta-annotation. In order to
* use this annotation as a meta-annotation, only use the {@link #name} attribute.
* @return the classes that must be present
*/
Class[] value() default {};
/**
* The classes names that must be present.
* @return the class names that must be present.
*/
String[] name() default {};
}