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。
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。
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。
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 "";
}
}
