Spring - @Conditional全解

短命女 2022-10-22 02:57 207阅读 0赞

### 文章目录 ###

*  作用
 *  扩展注解
 *  Code
 *   *  Bean1 Bean2
     *  自定义比较规则
     *  配置类
     *  测试类
 *  如何校验自动配置类是否生效

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70]

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# 作用 #

必须是@Conditional指定的条件成立，才给容器中添加组件，配置配里面的所有内容才生效

--------------------

# 扩展注解 #

<table> 
 <thead> 
  <tr> 
   <th align="left">@Conditional扩展注解</th> 
   <th align="left">作用（判断是否满足当前指定条件）</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">@ConditionalOnJava</td> 
   <td align="left">系统的java版本是否符合要求</td> 
  </tr> 
  <tr> 
   <td align="left">@ConditionalOnBean</td> 
   <td align="left">容器中存在指定Bean；</td> 
  </tr> 
  <tr> 
   <td align="left">@ConditionalOnMissingBean</td> 
   <td align="left">容器中不存在指定Bean；</td> 
  </tr> 
  <tr> 
   <td align="left">@ConditionalOnExpression</td> 
   <td align="left">满足SpEL表达式指定</td> 
  </tr> 
  <tr> 
   <td align="left">@ConditionalOnClass</td> 
   <td align="left">系统中有指定的类</td> 
  </tr> 
  <tr> 
   <td align="left">@ConditionalOnMissingClass</td> 
   <td align="left">系统中没有指定的类</td> 
  </tr> 
  <tr> 
   <td align="left">@ConditionalOnSingleCandidate</td> 
   <td align="left">容器中只有一个指定的Bean，或者这个Bean是首选Bean</td> 
  </tr> 
  <tr> 
   <td align="left">@ConditionalOnProperty</td> 
   <td align="left">系统中指定的属性是否有指定的值</td> 
  </tr> 
  <tr> 
   <td align="left">@ConditionalOnResource</td> 
   <td align="left">类路径下是否存在指定资源文件</td> 
  </tr> 
  <tr> 
   <td align="left">@ConditionalOnWebApplication</td> 
   <td align="left">当前是web环境</td> 
  </tr> 
  <tr> 
   <td align="left">@ConditionalOnNotWebApplication</td> 
   <td align="left">当前不是web环境</td> 
  </tr> 
  <tr> 
   <td align="left">@ConditionalOnJndi</td> 
   <td align="left">JNDI存在指定项</td> 
  </tr> 
 </tbody> 
</table>

--------------------

# Code #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 1]

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## Bean1 Bean2 ##

public class Bean1 { 
    
        public Bean1() { 
            System.out.println("我是Bean1的构造方法");
        }
    }

public class Bean2 { 
    
        public Bean2() { 
            System.out.println("我是Bean2的构造方法");
        }
    }

--------------------

## 自定义比较规则 ##

import org.springframework.context.annotation.Condition;
    import org.springframework.context.annotation.ConditionContext;
    import org.springframework.core.type.AnnotatedTypeMetadata;
    
    
    public class ArtisanCondition implements Condition { 
    
        @Override
        public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) { 
            //判断容器中是否有bean1的组件
            if(context.getBeanFactory().containsBean("bean1")) { 
                return true;
            }
            return false;
        }
    }

--------------------

## 配置类 ##

import com.tuling.testconditional.compent.Bean1;
    import com.tuling.testconditional.compent.Bean2;
    import com.tuling.testconditional.condition.ArtisanCondition;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Conditional;
    
    
    public class MainConfig { 
    
        @Bean
        public Bean1 bean1() { 
            return new Bean1();
        }
    
    	// 如果满足ArtisanCondition中定义的规则，就实例化Bean2 
        @Bean
        @Conditional(value = ArtisanCondition.class) 
        public Bean2 bean2() { 
            return new Bean2();
        }
    }

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## 测试类 ##

import com.tuling.testconditional.config.MainConfig;
    import org.springframework.context.annotation.AnnotationConfigApplicationContext;
    
    
    public class MainClass { 
    
        public static void main(String[] args) { 
            AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(MainConfig.class);
            for(String beanName:ctx.getBeanDefinitionNames()) { 
                System.out.println("beanName:"+beanName);
            }
    
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 2]

为了测试效果

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 3]

重新测试

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 4]

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# 如何校验自动配置类是否生效 #

配置文件中增加

启用 debug=true属性；来让控制台打印自动配置报告

![在这里插入图片描述][20210403114812707.jpg_pic_center]

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[20210403114812707.jpg_pic_center]: /images/20221022/934ccae471e64dc1b6f81763f84cc1ad.png