SpringBoot中InitializingBean接口和ApplicationContextAware接口

1. InitializingBean

• 这个接口 InitailizingBean中只有一个方法，就是afterPropertiesSet。该方法是指Spring容器在启动后主动调用该接口的方法。
• 如果一个Bean实现了InitializingBean，则该方法会在容器实例化该Bean，初始化Bean的属性完毕之后，再调用afterPropertiesSet方法。
• afterPropertiesSet通过方法名称即可知道含义：在bean的属性设置完毕后调用该方法。

接口InitializingBean接口源码如下：

public interface InitializingBean {

    /**
     * 当Bean的属性被设置完毕后，由BeanFactory调用该方法。
     * 该方法允许bean的实例去执行一些初始化动作，当所有的bean属性完成设置之后执行。   
     */
    void afterPropertiesSet() throws Exception;
}

2. ApplicationContextWare

• 名称带Aware，就可以知道这个接口由Spring容器主动通知调用。Spring容器在通知该接口的实现类时，会将上下文ApplicationContext注入进来。
• 接口中就一个方法：
  void setApplicationContext(ApplicationContext applicationContext) throws BeansException
• 即容器启动后，将ApplicationContext 注入到该方法中。

接口ApplicationContextWare源码如下：

public interface ApplicationContextAware extends Aware {
    void setApplicationContext(ApplicationContext var1) throws BeansException;
}

3. 例子

• 3.1 枚举类FamilyEnum

package com.example.demo.blogTest;

public enum FamilyEnum {
    FATHER(45, "father"),
    MOTHER(42, "mother"),
    SON(18, "son");

    private Integer age;
    private String name;
    FamilyEnum(Integer age, String name) {
        this.age = age;
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public String getName() {
        return name;
    }
}

• 3.2 自定义注入类FamilyHolder

package com.example.demo.blogTest;

import com.example.demo.service.BaseService;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

import java.util.HashMap;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

@Component
public class FamilyHolder implements InitializingBean, ApplicationContextAware {
    private ApplicationContext applicationContext;
    private Map<FamilyEnum, BaseService> map = new HashMap<>();

    public BaseService getEnum(FamilyEnum familyEnum) {
        return map.get(familyEnum);
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        map = applicationContext.getBeansOfType(BaseService.class)
                .values()
                .stream()
                .collect(Collectors.toMap(BaseService::getEnum, Function.identity()));
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
}

• 3.3 抽象类BaseService

package com.example.demo.service;

import com.example.demo.blogTest.FamilyEnum;

public abstract class BaseService {
    // 抽象工作类，具体实现由其继承者实现
    public abstract void myJob();

    public abstract FamilyEnum getEnum();

    // 通用方法，也可以被继承者重写
    public String getName(FamilyEnum person) {
        return person.getName();
    }
}

• 3.4 抽象继承类FatherService

package com.example.demo.service;

import com.example.demo.blogTest.FamilyEnum;
import org.springframework.stereotype.Service;

@Service
public class FatherService extends BaseService{
    @Override
    public void myJob() {
        System.out.println("I am a engineer!");
    }

    @Override
    public FamilyEnum getEnum() {
        return FamilyEnum.FATHER;
    }
}

• 3.5 抽象继承类MotherService

package com.example.demo.service;

import com.example.demo.blogTest.FamilyEnum;
import org.springframework.stereotype.Service;

@Service
public class MotherService extends BaseService{
    @Override
    public void myJob() {
        System.out.println("I am a teacher!");
    }

    @Override
    public FamilyEnum getEnum() {
        return FamilyEnum.MOTHER;
    }
}

• 3.6 抽象继承类MyService

package com.example.demo.service;

import com.example.demo.blogTest.FamilyEnum;
import org.springframework.stereotype.Service;

@Service
public class MyService extends BaseService{
    @Override
    public void myJob() {
        System.out.println("I am a student!");
    }

    @Override
    public FamilyEnum getEnum() {
        return FamilyEnum.SON;
    }
}

• 3.7 测试类DemoApplicationTests

package com.example.demo;

import com.example.demo.blogTest.FamilyEnum;
import com.example.demo.blogTest.FamilyHolder;
import com.example.demo.service.BaseService;
import org.junit.jupiter.api.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
class DemoApplicationTests {
    @Autowired
    private FamilyHolder familyHolder;

    @Test
    void contextLoads() throws ClassNotFoundException {
        // 通过反射获取所有枚举元素
        Class<FamilyEnum> clazz = (Class<FamilyEnum>) Class.forName("com.example.demo.blogTest.FamilyEnum");
        FamilyEnum[] enumConstants = clazz.getEnumConstants();
        for (FamilyEnum familyEnum : enumConstants) {
            BaseService baseService = familyHolder.getEnum(familyEnum);
            baseService.myJob();
        }
    }
}

• 输出结果

I am a engineer!
I am a teacher!
I am a student!

4. 参考文献

• https://blog.youkuaiyun.com/douunderstand/article/details/78835515
• https://blog.youkuaiyun.com/junchenbb0430/article/details/78606380?utm_medium=distribute.pc_relevant.none-task-blog-baidujs_title-3&spm=1001.2101.3001.4242