全注解下的spring IOC之依赖注入

喜欢ヅ旅行 2022-05-13 19:16 208阅读 0赞

主要讲IOC容器如何加载bean之间的依赖关系和bean值得获取。

## 案例 ##

Person接口

package com.wuk.demo4;
    
    public interface Person {
    
    	/*使用动物服务*/
    	public void service();
    	
    	/*设置动物*/
    	public void setAnimal(Animal animal);
    	
    }

Animal接口

package com.wuk.demo4;
    
    public interface Animal {
    
    	public void use();
    }

BusinessPerson 类

package com.wuk.demo4;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Component;
    
    @Component
    public class BusinessPerson implements Person {
    	
    	//该注解会根据属性类型在IOC中找到相对应的对象bean的值并注入
    	@Autowired
    	private Animal animal;
    	
    	@Override
    	public void service() {
    		
    		this.animal.use();
    	}
    
    	@Override
    	public void setAnimal(Animal animal) {
    		
    		this.animal=animal;
    	}
    
    }

Dog类

package com.wuk.demo4;
    
    import org.springframework.stereotype.Component;
    
    //表示这个类将被springIOC容器扫描装配
    @Component
    public class Dog implements Animal {
    
    	@Override
    	public void use() {
    		
    		System.out.println("狗"+Dog.class.getSimpleName()+"是用来看门的");
    	}
    
    }

AppConfig 配置类

package com.wuk.demo4;
    
    import org.springframework.context.annotation.ComponentScan;
    import org.springframework.context.annotation.Configuration;
    
    //表示它会进行扫描，只扫描该类所在额包和子包
    @ComponentScan
    //表示这是一个配置文件
    @Configuration
    public class AppConfig {
    
    }

测试类

package com.wuk.demo4;
    
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.annotation.AnnotationConfigApplicationContext;
    
    public class IocTest4 {
    
    	public static void main(String[] args) {
    		
    		ApplicationContext app=new AnnotationConfigApplicationContext(AppConfig.class);
    		
    		Person person=app.getBean(BusinessPerson.class);
    		person.service();
    	}
    }

结果

狗Dog是用来看门的

## 注解@Autowired ##

注入的机制是根据类型。  
如果我们现在再创建一个Cat类

package com.wuk.demo4;
    
    import org.springframework.stereotype.Component;
    
    //表示这个类将被springIOC容器扫描装配
    @Component
    public class Cat implements Animal {
    
    	@Override
    	public void use() {
    		
    		System.out.println("猫"+Cat.class.getSimpleName()+"是用来抓老鼠的");
    	}
    
    }

如果再执行上述代码，就会报错如下：

Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.wuk.demo4.Animal' available: expected single matching bean but found 2: cat,dog
    	at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:215)
    	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1113)
    	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1062)
    	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:581)
    	... 14 more

现在对BusinessPerson类中的animal修改为dog

package com.wuk.demo4;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Component;
    
    @Component
    public class BusinessPerson implements Person {
    	
    	//该注解会根据属性类型在IOC中找到相对应的对象bean的值并注入
    	@Autowired
    	private Animal dog;
    	
    	@Override
    	public void service() {
    		
    		this.dog.use();
    	}
    
    	@Override
    	public void setAnimal(Animal animal) {
    		
    		this.dog=animal;
    	}
    
    }

异常消失。  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3d1MjM3NDYzMzU4Mw_size_27_color_FFFFFF_t_70][]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3d1MjM3NDYzMzU4Mw_size_27_color_FFFFFF_t_70 1]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3d1MjM3NDYzMzU4Mw_size_27_color_FFFFFF_t_70 2]

## 消除歧义性-@Primary和@Qualifier ##

package com.wuk.demo4;
    
    import org.springframework.context.annotation.Primary;
    import org.springframework.stereotype.Component;
    
    @Primary
    @Component
    public class Cat implements Animal {
    
    	@Override
    	public void use() {
    		
    		System.out.println("猫"+Cat.class.getSimpleName()+"是用来抓老鼠的");
    	}
    
    }

**@Primary就是告诉IOC，当发现多个相同类型的Bean时候，请优先使用我进行注入。**  
但是问题又来了，如果有多个类上使用@Primary怎么办？

@Qualifier("dog")
    	@Autowired
    	private Animal animal;

**@Qualifier(“dog”) 这样IOC容器就会根据类型和名称去寻找对应的Bean进行注入。**

## 带有参数的构造方法类的装配 ##

在上述中我们都是基于一种情况，就是在不带参数的构造方法下实现依赖注入。

package com.wuk.demo4;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.beans.factory.annotation.Qualifier;
    import org.springframework.stereotype.Component;
    
    @Component
    public class BusinessPerson implements Person {
    
    	private Animal animal;
    	
    	public BusinessPerson(@Autowired @Qualifier("dog") Animal animal){
    		
    		this.animal=animal;
    	}
    	
    	@Override
    	public void service() {
    		
    		this.animal.use();
    	}
    
    	@Override
    	public void setAnimal(Animal animal) {
    		
    		this.animal=animal;
    	}
    
    }

**public BusinessPerson(@Autowired @Qualifier(“dog”) Animal animal)**

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3d1MjM3NDYzMzU4Mw_size_27_color_FFFFFF_t_70]: /images/20220504/a97e41db3d5844fe9043146beea13df8.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3d1MjM3NDYzMzU4Mw_size_27_color_FFFFFF_t_70 1]: /images/20220504/ef7326851c4b4bb3b2bb71e56d600f3f.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3d1MjM3NDYzMzU4Mw_size_27_color_FFFFFF_t_70 2]: /images/20220504/57c82184a428409989f529056e014589.png