@ConditionalOnBean、@ConditionalOnProperty、@ConditionalOnClass、@Conditional和Condition接口的使用

亦凉 2022-11-12 02:54 226阅读 0赞

### 一、@ConditionalOnBean、@ConditionalOnProperty、@ConditionalOnClass ###

**@ConditionalOnBean是指当spring容器中有某个bean时才装配。@ConditionalOnMissingBean当spring容器中不存在某个bean时才装配**

**@ConditionalOnClass是指当classpath下有某个类时才装配。@ConditionalOnMissingClass是指当classpath下没有某个类时才装配**

**@ConditionalOnProperty是指当某个配置项为某个值时才装配。@ConditionalOnMissingProperty是指当某个配置项不等于某个值时才装配**

例如：@ConditionalOnBean(name="user")表示当容器中有名字为user的bean时才装配。

下面做下验证测试：

第一步：当没有任何注解时，spring容器里会有三个Runnable类型的bean，名字分别为createRable1，createRable2，createRable3

package com.lsl;
    
    import org.springframework.boot.SpringBootConfiguration;
    import org.springframework.context.annotation.Bean;
    
    @SpringBootConfiguration
    public class MyConfig {
    
        @Bean
        public Runnable createRable1(){
            System.out.println("=======default======");
            return ()->{};
        }
    
        @Bean
        public Runnable createRable2(){
            System.out.println("=======dev======");
            return ()->{};
        }
    
        @Bean
        public Runnable createRable3(){
            System.out.println("=======user======");
            return ()->{};
        }
    }

package com.lsl;
    
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    import org.springframework.context.ConfigurableApplicationContext;
    
    @SpringBootApplication
    public class SpringbootProviderApplication {
    
        public static void main(String[] args) {
            ConfigurableApplicationContext content = SpringApplication.run(SpringbootProviderApplication.class, args);
            System.out.println("springname=" + content.getEnvironment().getProperty("springboot.name"));
            System.out.println("ds.name="  + content.getEnvironment().getProperty("ds.name"));
            System.out.println("ds.password="  + content.getEnvironment().getProperty("ds.password"));
    
            //从容器中获取类型为Runnable的所有bean
            System.out.println(content.getBeansOfType(Runnable.class));
        }
    
    }

输出结果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Roa2xzbA_size_16_color_FFFFFF_t_70][]

第二步：当分别加上注解时

package com.lsl;
    
    import org.springframework.boot.SpringBootConfiguration;
    import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
    import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
    import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
    import org.springframework.context.annotation.Bean;
    
    @SpringBootConfiguration
    public class MyConfig {
    
        @Bean
        @ConditionalOnBean(name="user")
        public Runnable createRable1(){
            System.out.println("=======default======");
            return ()->{};
        }
    
        @Bean
        @ConditionalOnClass(name="user")
        public Runnable createRable2(){
            System.out.println("=======dev======");
            return ()->{};
        }
    
        @Bean
        @ConditionalOnProperty(name="opFlag",havingValue = "save")
        public Runnable createRable3(){
            System.out.println("=======user======");
            return ()->{};
        }
    }

结果输出：由于没有user的bean所以没有装配

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Roa2xzbA_size_16_color_FFFFFF_t_70 1][]

第三步：创建User类，并交给spring容器托管。

package com.lsl;
    
    import org.springframework.stereotype.Component;
    
    @Component
    public class User {
    }

输出结果：由于spring容器托管了User类，名字且为user，所以createRable1装配了

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Roa2xzbA_size_16_color_FFFFFF_t_70 2][]

在默认配置文件加上配置项 ，createRable3也装配了

![20210322171152359.png][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Roa2xzbA_size_16_color_FFFFFF_t_70 3][]

由于classpath下没有user的bean，所有createRable2没有被装配。

### 二、@Conditional和Condition接口 ###

上面的三个注解时spring提供的比较常用的几个注解，当然spring还提供了其他类似注解，

比如@ConditionalOnJava，当jdk为某个版本时才装配。

除此之外spring还提供了扩展，利用Condition接口和@Conditional注解自定义扩展功能

**一般情况下Condition接口和@Conditional注解要配合使用。**

首先是实现Condition接口。

package com.lsl;
    
    import org.springframework.context.annotation.Condition;
    import org.springframework.context.annotation.ConditionContext;
    import org.springframework.core.type.AnnotatedTypeMetadata;
    
    import java.util.Arrays;
    import java.util.List;
    
    public class MyCondition implements Condition {
        @Override
        public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
            String opFlag = conditionContext.getEnvironment().getProperty("opFlag");
            String[] beanDefinitionNames = conditionContext.getRegistry().getBeanDefinitionNames();
            List<String> strings = Arrays.asList(beanDefinitionNames);
            if (strings.contains("user" ) && "save".equals(opFlag)){
                return true;
            }
            return false;
        }
    }

createRable4（）方法上加了 @Conditional(MyCondition.class)注解，表示只有当MyCondition中的方法返回true时才装配。

package com.lsl;
    
    import org.springframework.boot.SpringBootConfiguration;
    import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
    import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
    import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Conditional;
    
    @SpringBootConfiguration
    public class MyConfig {
    
        @Bean
        @ConditionalOnBean(name="user")
        public Runnable createRable1(){
            System.out.println("=======default======");
            return ()->{};
        }
    
        @Bean
        @ConditionalOnClass(name="user")
        public Runnable createRable2(){
            System.out.println("=======dev======");
            return ()->{};
        }
    
        @Bean
        @ConditionalOnProperty(name="opFlag",havingValue = "save")
        public Runnable createRable3(){
            System.out.println("=======user======");
            return ()->{};
        }
    
        @Bean
        @Conditional(MyCondition.class)
        public Runnable createRable4(){
            System.out.println("=======MyCondition======");
            return ()->{};
        }
    }

输出结果如下：MyCondition的功能是当配置项opFlag=save且容器中已经注册了user名字的bean时才返回true

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Roa2xzbA_size_16_color_FFFFFF_t_70 4][]

这种配合使用的方法非常灵活，可以多看看Condition接口中matchs方法的两个参数，这2个参数能获取好多信息，可以根据信息进行相关逻辑判断是返回true还是false.

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Roa2xzbA_size_16_color_FFFFFF_t_70]: /images/20221022/398ad4deabe14fe0b2731e74aa8f1529.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Roa2xzbA_size_16_color_FFFFFF_t_70 1]: /images/20221022/27ff0856def942409a1fda0f05532bfb.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Roa2xzbA_size_16_color_FFFFFF_t_70 2]: /images/20221022/a4dc148e5ebf45ad86bfd1a60541e1f2.png
[20210322171152359.png]: /images/20221022/7c01a195dc5444d4b8dcad5ef97cdcf2.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Roa2xzbA_size_16_color_FFFFFF_t_70 3]: /images/20221022/7aa820ae4f7742029211dc08c68391d8.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Roa2xzbA_size_16_color_FFFFFF_t_70 4]: /images/20221022/63473133e2a2487284df3835b281a59f.png