配置类 Config

@Configuration
@ComponentScan
public abstract class Config{}




Pet接口  
默认方法
public default void hello(){
		System.out.println(this.toString()+",say hello,"+new Date());
}


Cat Dog Tiger 实现 Pet接口

scans.Cat
scans.a.Dog
scans.b.Tiger

@ComponentScan 不设置扫描路径 会扫描配置所在包及子包

@ComponentScan({"scans"})  扫描 scans 包及子包


@Component
public class Zoo{
	@Autowired
	private Cat cat;

	@Autowired
	private Dog dog;

	@Autowired
	private Tiger tiger;





@Autowired
private Pet cat3;
org.springframework.beans.factory.NoUniqueBeanDefinitionException: 
No qualifying bean of type 'scans.Pet' available: expected single matching bean but found 3: cat,dog,tiger

使用 @Qualifier 消除歧义

@Autowired
@Qualifier("cat")
private Pet cat3;


@Autowired @Qualifier("cat")


或者 

@Resource(name="cat")
private Pet cat3;

同时写上 也 ok 
@Resource(name="cat")
@Autowired @Qualifier("cat")


注释 Dog 上的 @Component 注解

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'scans.a.Dog' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

可设置 required 为 false 
@Autowired(required=false)

@Resource 注解无法实现类似功能


@Autowired(required=false) @Qualifier("catNotExist")
private Pet cat4;



@ComponentScan({"a.b.c","x.y.z"})

@ComponentScans  可 配置对个  @ComponentScan

@ComponentScans({@ComponentScan("a.b"),@ComponentScan("x.y")})

@ComponentScans({@ComponentScan({"a.b","x.y"})})