Spring-条件注入(条件装配)-实例

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。

本文的条件注解，如无特殊说明，都可以放到如下几个地方：有@Component的类、有@Configuration的类、有@Bean的方法。

相关网址

Spring–条件注入(条件装配)–详解 – 自学精灵

@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 "";
    }
}