1、通过@Value的方式

package com.ec.demo;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "MyBean{" +
                "name='" + name + '\'' +
                '}';
    }

    @Value("${name}")
    private String name;
}

package com.ec.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@EnableConfigurationProperties(Mail.class)
@RestController
@SpringBootApplication
public class DemoApplication {

    @Autowired
    private MyBean myBean;

    @Autowired
    private Mail mail;

    @RequestMapping("/")
    String home() {
        return myBean.toString();
    }

    @RequestMapping("/mail")
    String mail() {
//        Mail mail = new Mail();
        return mail.toString();
    }

    public static void main(String[] args) throws Exception {
        SpringApplication.run(DemoApplication.class, args);
    }
}

2、通过@ConfigurationProperties的方式

package com.ec.demo;

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

@ConfigurationProperties(prefix = "mail")
public class Mail {

    private String name;
    private String secret;
    private Integer ssl;

    @Override
    public String toString() {
        return "Mail{" +
                "name='" + name + '\'' +
                ", secret='" + secret + '\'' +
                ", ssl=" + ssl +
                '}';
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSecret() {
        return secret;
    }

    public void setSecret(String secret) {
        this.secret = secret;
    }

    public Integer getSsl() {
        return ssl;
    }

    public void setSsl(Integer ssl) {
        this.ssl = ssl;
    }
}

注意，要在主类中添加@EnableConfigurationProperties(Mail.class)，而且两种方式都要通过@Autowired的方式注入对象，不能自己new