Spring示例讲解条件注入方法
作者:IT利刃出鞘
Spring支持按照条件来注入某些特定的bean,这也是Spring Boot实现自动化配置的底层方法,文中的示例代码讲解详细,需要的可以参考一下
简介
说明
本文用实例介绍Spring的条件注入的用法。
@Component、@Configuration+@Bean都可以与条件注入的注解结合。
@Component+条件注解
Bean
package com.example.config; import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty; import org.springframework.stereotype.Component; @Component @ConditionalOnProperty(name = "custom.myComponent.enabled", havingValue = "true") public class MyComponent { public MyComponent() { System.out.println("[MyComponent#MyComponent]"); } }
application.yml
custom:
myComponent:
enabled: true
运行结果:
[MyComponent#MyComponent]
若将application.yml的custom.myComponent.enabled去掉,或者设置为非true值,则不会输出上边的运行结果。
@Configuration+@Bean+条件注解
Bean
package com.example.config; public class MyComponent { public MyComponent() { System.out.println("[MyComponent#MyComponent]"); } }
配置类
package com.example.config; import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class MyConfig { @Bean @ConditionalOnProperty(name = "custom.myComponent.enabled", havingValue = "true") public MyComponent getMyComponent() { return new MyComponent(); } }
application.yml
custom:
myComponent:
enabled: true
运行结果:
[MyComponent#MyComponent]
若将application.yml的custom.myComponent.enabled去掉,或者设置为非true值,则不会输出上边的运行结果。
@Configuration+条件注解+@Bean
Bean
package com.example.config; public class MyComponent { public MyComponent() { System.out.println("[MyComponent#MyComponent]"); } }
配置类
package com.example.config; import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration @ConditionalOnProperty(name = "custom.myComponent.enabled", havingValue = "true") public class MyConfig { @Bean public MyComponent getMyComponent() { return new MyComponent(); } }
application.yml
custom:
myComponent:
enabled: true
运行结果:
[MyComponent#MyComponent]
若将application.yml的custom.myComponent.enabled去掉,或者设置为非true值,则不会输出上边的运行结果。
自定义Condition
自定义的condition的matches方法返回值为true时,才会创建bean。
条件类
//判断当前系统是否是Mac
import org.springframework.context.annotation.Condition; import org.springframework.context.annotation.ConditionContext; import org.springframework.core.type.AnnotatedTypeMetadata; public class MyCondition implements Condition { @Override public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) { return conditionContext.getEnvironment().getProperty("os.name").contains("Mac"); } }
@Configuration public class Config { @Conditional(MyCondition.class) @Bean public String condition() { System.err.println("This is mac"); return ""; } }
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