@Conditional根据满足某特定条件创建特定的Bean

package com.tszr.conditional;

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 context, AnnotatedTypeMetadata metadata) {
        return context.getResourceLoader().getResource("classpath:test.properties").exists();
    }
}

package com.tszr.conditional;

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

public class YourCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        return !context.getResourceLoader().getResource("classpath:test.properties").exists();
    }
}

package com.tszr.dao;

public interface MessagePrint {
    public String showMessage();
}

package com.tszr.service;

import com.tszr.dao.MessagePrint;

public class MyMessagePrint implements MessagePrint {
    @Override
    public String showMessage() {
        return "test.properties文件存在。";
    }
}

package com.tszr.service;

import com.tszr.dao.MessagePrint;

public class YourMessagePrint implements MessagePrint {
    @Override
    public String showMessage() {
        return "test.properties文件不存在！";
    }
}

package com.tszr.controller;

import com.tszr.conditional.MyCondition;
import com.tszr.conditional.YourCondition;
import com.tszr.dao.MessagePrint;
import com.tszr.service.MyMessagePrint;
import com.tszr.service.YourMessagePrint;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;

@Configuration
public class ConditionConfig {
    @Bean
    @Conditional(MyCondition.class)
    public MessagePrint myMessage() {
        return new MyMessagePrint();
    }
    @Bean
    @Conditional(YourCondition.class)
    public MessagePrint yourMessage() {
        return new YourMessagePrint();
    }
}

package com.tszr.conditional;

import com.tszr.controller.ConditionConfig;
import com.tszr.dao.MessagePrint;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class TestMain {
    private static AnnotationConfigApplicationContext context;
    public static void main(String[] args) {
        context = new AnnotationConfigApplicationContext(ConditionConfig.class);
        MessagePrint mp = context.getBean(MessagePrint.class);
        System.out.println(mp.showMessage());
    }
}