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Spring(SpringBoot)--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。

@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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