SpringBoot中@Conditional注解的使用

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Conditional {
	// 自定义类实现Condition接口，完成给出指定的条件。
	Class<? extends Condition>[] value();
}

public class MyCondition implements Condition {
    /**
     * @param context: 判断条件使用的上下文环境
     * @param metadata: 扫描的注解信息
     */
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        // 1. 获取bean工厂
        ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
        // 2. 获取运行环境, 可以根据操作系统的环境进行限制bean
        Environment environment = context.getEnvironment();
        // 3. 获取BeanDefinition注册定义表
        context.getRegistry();
        // 4. 获取资源加载器
        context.getResourceLoader();
        // 5. 获取类加载器
        ClassLoader classLoader = context.getClassLoader();
        if (beanFactory.containsBean("dog1")) {
            return false;
        }
        /**
         *      可以根据以上条件进行条件装配
         *      true: 装配
         *      false： 不装配
         */
        return true;
    }
}

@Configuration
public class MyConfig {
    @Bean("user1")
    public User user1(){
        return new User("splay", 22, "男");
    }
    @Bean("dog1")
    //@ConditionalOnBean(name = {"dog2"})
    public Dog dog1(){
        return new Dog("金毛", 4,"公");
    }
    @Bean("dog2")
    @Conditional(value = MyCondition.class)
    public Dog dog2(){
        return new Dog("拉布拉多", 3,"母");
    }
}

@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnBeanCondition.class)			//OnBeanCondition是一个Condition接口的实现类
public @interface ConditionalOnBean {

	// 1. 按照bean的类型进行检查
	Class<?>[] value() default {};

	// 2. 按照bean的类型进行检查
	String[] type() default {};

	// 3. 按照bean的注解进行检查
	Class<? extends Annotation>[] annotation() default {};

	// 4. 按照BeanName进行检查
	String[] name() default {};

	// 5. 搜索策略
	SearchStrategy search() default SearchStrategy.ALL;

	// 6. 不详
	Class<?>[] parameterizedContainer() default {};
}

@Configuration
public class MyConfig {

    @Bean("user1")
    public User user1(){
        return new User("splay", 22, "男");
    }


    @Bean("dog1")
    public Dog dog1(){
        return new Dog("金毛", 4,"公");
    }

    @Bean("dog2")
    @ConditionalOnBean(name = {"dog1"})
    public Dog dog2(){
        return new Dog("拉布拉多", 3,"母");
    }
}

@Configuration
public class MyConfig {

    @Bean("user1")
    public User user1(){
        return new User("splay", 22, "男");
    }


    @Bean("dog1")
    @ConditionalOnBean(name = {"dog2"})		//当有dog2组件的时候创建dog1
    public Dog dog1(){
        return new Dog("金毛", 4,"公");
    }

    @Bean("dog2")
    public Dog dog2(){
        return new Dog("拉布拉多", 3,"母");
    }
}