步驟
使用@interface 自定義注解
編寫注解處理類，實現BeanPostProcessor接口
原理
實現BeanPostProcessor接口的類即為Bean后置處理器，Spring加載機制會在所有Bean初始化的時候遍歷調用每個Bean后置處理器。
其順序為：Bean實例化-》依賴注入-》Bean后置處理器-》@PostConstruct

缺陷
只有在會實例化成Bean的類中使用，注解才會生效。（因為是使用了Bean后置處理器實現的嘛）

代碼示例
完整參考代碼github

自定義注解接口

import org.springframework.stereotype.Component;
import java.lang.annotation.*;

@Target({ElementType.FIELD}) //聲明應用在屬性上
@Retention(RetentionPolicy.RUNTIME) //運行期生效
@Documented //Java Doc
@Component
public @interface Boy {
    String value() default "";
}

注解處理類

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;

import java.lang.reflect.Field;

@Component //注意：Bean后置處理器本身也是一個Bean
public class BoyAnnotationBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        /**
         * 利用Java反射機制注入屬性
         */
        Field[] declaredFields = bean.getClass().getDeclaredFields();
        for (Field declaredField : declaredFields) {
            Boy annotation = declaredField.getAnnotation(Boy.class);
            if (null == annotation) {
                continue;
            }
            declaredField.setAccessible(true);
            try {
                declaredField.set(bean, annotation.value());
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        }
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object o, String s) throws BeansException {
        return o; //這里要返回o，不然啟動時會報錯
    }
}

注解使用類

import org.springframework.stereotype.Service;
import javax.annotation.PostConstruct;

@Service
public class HelloBoy {

    @Boy("小明")
    String name = "world";

    public void sayHello() {
        System.out.println("hello, " + name);
    }
}

測試類

import com.markey.annotations.Boy.HelloBoy;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class HelloBoyTest {

    @Autowired
    HelloBoy helloBoy;

    @Test
    public void HelloBoyTest() {
        helloBoy.sayHello();
    }

}

注解無效示例
測試類

import com.markey.annotations.Boy.HelloBoy;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class HelloBoyTest {

    HelloBoy helloBoy = new HelloBoy(); //新建的對象，不是容器中的Bean
    @Test
    public void HelloBoyTest() {
        helloBoy.sayHello();
    }
}

Tips
其實Spring很多原生注解（例如@Autowired，其處理類是AutowiredAnnotationBeanPostProcessor）,也是通過實現BeanPostProcessor接口這種方式來實現的。