上一篇文章：https://createdpro.com/a/51000351764

上篇文章主要介绍了下springboot自动配置的特性，为了协助理解，我们可以自己定义一个bean交给springboot的自动配置进行注入。

本案例仅存在练习之用，无任何业务能力。

首先创建我们要自动配置的bean的类，这个类有一个销售苹果的业务方法：

package com.test.starter.apple;

import com.test.starter.autoconfig.AppleProperties;

public class SellApple {

    private AppleProperties appleProperties;

    public SellApple(AppleProperties appleProperties) {
        this.appleProperties = appleProperties;
    }

    public void sell() {
        System.out.println(appleProperties.getColor()
                + "色的苹果"
                + appleProperties.getWeight()
                + "斤重，价格是"
                + appleProperties.getPrice());
    }
}

然后我们创建AppleProperties这个配置类，我们为每项属性设定了默认值，我们可以通过全局配置文件application.yml进行值得覆盖设置：

package com.test.starter.autoconfig;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties(prefix = "createdpro.apple")
public class AppleProperties {

    // 这里设置的值是默认值
    // 当使用全局配置文件配置如上前缀时，该值会被覆盖
    private Integer weight = 5;

    private String color = "red";

    private double price = 7.9;

    public Integer getWeight() {
        return weight;
    }
    public void setWeight(Integer weight) {
        this.weight = weight;
    }
    public String getColor() {
        return color;
    }
    public void setColor(String color) {
        this.color = color;
    }
    public double getPrice() {
        return price;
    }
    public void setPrice(double price) {
        this.price = price;
    }
}

接下来我们创建HttpClientAutoConfiguration这个类，实现配置的方法：

package com.test.starter.autoconfig;

import com.test.starter.apple.SellApple;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@ConditionalOnClass({SellApple.class})
@EnableConfigurationProperties(AppleProperties.class)
public class AppleAutoConfiguration {

    private final AppleProperties appleProperties;

    public AppleAutoConfiguration(AppleProperties appleProperties) {
        this.appleProperties = appleProperties;
    }

    @Bean
    @ConditionalOnMissingBean(SellApple.class)
    public SellApple sellApple() {
        return new SellApple(appleProperties);
    }

}

接下来创建测试类：

package com.test.stater;

import com.test.stater.apple.SellApple;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
class DemoApplicationTests {

    @Autowired
    private SellApple sellApple;

    @Test
    void sellTest() {
        sellApple.sell();
    }

}

运行测试方法，发现在应用被启动后，bean被自动配置并创建了。

接下来我们通过全局配置文件application.yml配置一下Apple的属性：

applcation.yml

createdpro:
  apple:
    weight: 10
    color: green

再一次执行测试方法：

配置的默认值已经被覆盖了，使用了我们在全局配置applcation.yml中的值。