Spring注解——使用@Conditional来按照条件注册bean

1.有时候需要根据不同条件生成不同的 bean，这时候就需要用到 @Conditional 注解。常见的一种用法，就是根据操作系统类型，注册不同的 bean。在 BeanConfig 配置类中增加三个 bean。

package io.mieux.config;

import io.mieux.bean.Person;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class BeanConfig {

    @Bean(value = "zhangsan")
    public Person getPerson() {
        return new Person("zhangsan", 28);
    }

    @Bean(value = "linux")
    public Person getLinux() {
        return new Person("linux", 50);
    }

    @Bean(value = "windows")
    public Person getWindows() {
        return new Person("windows", 30);
    }

    @Bean(value = "mac")
    public Person getMac() {
        return new Person("mac", 24);
    }
}

查看当前容器中 Person 类的实例有哪些：

package io.mieux;

import io.mieux.bean.Person;
import io.mieux.config.BeanConfig;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class App04 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(BeanConfig.class);
        String[] beanNames = annotationConfigApplicationContext.getBeanNamesForType(Person.class);
        for (String beanName : beanNames) {
            System.out.println("beanName: " + beanName);
        }
    }
}

运行效果：

beanName: zhangsan
beanName: linux
beanName: windows
beanName: mac

2.使用 @Conditional 注解来根据操作系统的不同注册不同的 bean。首先需要实现 Condition 接口，创建三个 Condition 接口的实现类 LinuxConditon、MacConditon 和 WindowsConditon，获取运行环境的操作系统类型进行判断。

LinuxConditon：

package io.mieux.condition;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.env.Environment;
import org.springframework.core.type.AnnotatedTypeMetadata;

// 判断是否是 linux 系统
public class LinuxConditon implements Condition {

    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        Environment environment = context.getEnvironment();

        String operatingSystem = environment.getProperty("os.name");
        if ("linux".equals(operatingSystem)) {
            System.out.println("Operating System: " + environment.getProperty("os.name"));
            return true;
        }
        return false;
    }
}

WindowsConditon：

package io.mieux.condition;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.env.Environment;
import org.springframework.core.type.AnnotatedTypeMetadata;

// 判断是否是 windows 系统
public class WindowsConditon implements Condition {

    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        Environment environment = context.getEnvironment();

        String operatingSystem = environment.getProperty("os.name");
        if (operatingSystem.contains("Windows")) {
            System.out.println("Operating System: " + environment.getProperty("os.name"));
            return true;
        }
        return false;
    }
}

MacConditon：

package io.mieux.condition;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.env.Environment;
import org.springframework.core.type.AnnotatedTypeMetadata;

// 判断是否是 mac os 系统
public class MacConditon implements Condition {

    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        Environment environment = context.getEnvironment();

        String operatingSystem = environment.getProperty("os.name");
        if ("Mac OS X".equals(operatingSystem)) {
            System.out.println("Operating System: " + environment.getProperty("os.name"));
            return true;
        }
        return false;
    }
}

在 BeanConfig 配置类中加上 @Conditional 注解。

package io.mieux.config;

import io.mieux.bean.Person;
import io.mieux.condition.LinuxConditon;
import io.mieux.condition.MacConditon;
import io.mieux.condition.WindowsConditon;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;

@Configuration
public class BeanConfig {

    @Bean(value = "zhangsan")
    public Person getPerson() {
        return new Person("zhangsan", 28);
    }

    @Bean(value = "linux")
    @Conditional(value = {LinuxConditon.class})
    public Person getLinux() {
        return new Person("linux", 50);
    }

    @Bean(value = "windows")
    @Conditional(value = {WindowsConditon.class})
    public Person getWindows() {
        return new Person("windows", 30);
    }

    @Bean(value = "mac")
    @Conditional(value = {MacConditon.class})
    public Person getMac() {
        return new Person("mac", 24);
    }
}

运行效果：

Operating System: Mac OS X
beanName: zhangsan
beanName: mac