@Conditional系列註解例子

1. @Conditional

說明：指定的Condition實現類，matches方法返回true則注入bean，false則不注入

@Configuration
public class BeanConfig {
 
    //只有一個類時，大括號能夠省略
    //若是WindowsCondition的實現方法返回true，則注入這個bean    
    @Conditional({WindowsCondition.class})
    @Bean(name = "bill")
    public Person person1(){
        return new Person("Bill Gates",62);
    }
 
    //若是LinuxCondition的實現方法返回true，則注入這個bean
    @Conditional({LinuxCondition.class})
    @Bean("linus")
    public Person person2(){
        return new Person("Linus",48);
    }
}

建立 LinuxCondition和 WindowsCondition類，並實現Condition接口

public class LinuxCondition implements Condition {
 
    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
 
        Environment environment = conditionContext.getEnvironment();
 
        String property = environment.getProperty("os.name");
        if (property.contains("Linux")){
            return true;
        }
        return false;
    }
}

 

2. @ConditionalOnBean

說明：僅僅在當前上下文中存在某個對象時，纔會實例化一個Bean

//RedisOperBean依賴redisTemplate
@Component
@ConditionalOnBean(name="redisTemplate")
public class RedisOperBean {
  private final RedisTemplate redisTemplate;
  public RedisOperBean(RedisTemplate redisTemplate) {
      // ...
  }
}

 

3. @ConditionalOnClass

說明：某個class位於類路徑上，纔會實例化一個Bean，要求指定的class必須存在

 

4. @ConditionalOnProperty

說明：

(1)matchIfMissing：從application.properties中讀取某個屬性值，若是該值爲空，默認值爲true

(2)havingValue：經過其兩個屬性name以及havingValue來實現的，其中name用來從application.properties中讀取某個屬性值，若是該值爲空，則返回false;

　　　　　　　　若是值不爲空，則將該值與havingValue指定的值進行比較，若是同樣則返回true;不然返回false。若是返回值爲false，則該configuration不生效；爲true則生效。

@Configuration
@ConditionalOnClass({ Feign.class })
@ConditionalOnProperty(value = "feign.oauth2.enabled", havingValue = "true", matchIfMissing = true)
public class OAuth2FeignAutoConfiguration {

    @Bean
    @ConditionalOnBean(OAuth2ClientContext.class)
    public RequestInterceptor oauth2FeignRequestInterceptor(OAuth2ClientContext oauth2ClientContext) {
        return new OAuth2FeignRequestInterceptor(oauth2ClientContext);
    }
}

 

5.@ConditionalOnMissingBean

說明：僅僅在當前上下文中不存在某個對象時，纔會實例化一個Bean

@Bean
    @ConditionalOnMissingBean(name = "imageValidateCodeGenerator")
    public ValidateCodeGenerator imageValidateCodeGenerator() {
        ImageCodeGenerator codeGenerator = new ImageCodeGenerator();
        codeGenerator.setSecurityProperty(securityProperties);
        return codeGenerator;
    }

 

6.@ConditionalOnMissingClass

說明：某個class類路徑上不存在的時候，纔會實例化一個Bean

 

7.@ConditionalOnExpression

說明：當表達式爲true的時候，纔會實例化一個Bean

@Configuration
@ConditionalOnExpression("${enabled:false}")
public class BigpipeConfiguration {
    @Bean
    public OrderMessageMonitor orderMessageMonitor(ConfigContext configContext) {
        return new OrderMessageMonitor(configContext);
    }
}

其餘樣式：

@ConditionalOnExpression("${mq.cumsumer.enabled}==1&&${rabbitmq.comsumer.enabled:true}")


@ConditionalOnExpression("'${mq.comsumer}'.equals('rabbitmq')")

 

8.@ConditionalOnNotWebApplication

說明：當前不是web應用

 

9.@ConditionalOnWebApplication

說明：當前是web應用

 

10. @ConditionalOnResource

說明：類路徑下是否存在指定的資源文件

@Bean
@ConditionalOnResource(resources="classpath:shiro.ini")
protected Realm iniClasspathRealm(){

}