一、常用注解

1、ComponentScan

ComponentScan主要就是定义扫描的路径，从中找出标识了需要装配的类自动装配到spring的bean容器中

2、Autowired和Resource

区别:

1.2.1、@Autowired

由Spring提供，只按照byType注入，可以配合@Qualifier一起使用

1.2.2、@Resource

由J2EE提供，默认按照byName自动注入

@Resource有两个重要的属性：name和type

1.2.3、当一个service有多个实现类时

1)、方式一

public interface UserService {void show();
}@Slf4j
@Service
public class UserServiceImpl implements UserService {@Overridepublic void show() {log.info("=======UserService-----UserServiceImpl=======");}
}@Slf4j
@Service
public class UserServiceEs implements UserService {@Overridepublic void show() {log.info("=======UserService-----UserServiceEs=======");}
}

@RestController
public class TestController {@Autowired@Qualifier("userServiceImpl")private UserService userService;//通过type@Resource(type = UserServiceEs.class)private UserService userServiceEs;@GetMapping("/hello")public String test() {userService.show();userServiceEs.show();return "hello ma!!!";}
}执行结果=======UserService-----UserServiceImpl==============UserService-----UserServiceEs=======

2)、方式二

public interface UserService {void show();
}@Slf4j
@Service("userServiceImpl")
public class UserServiceImpl implements UserService {@Overridepublic void show() {log.info("=======UserService-----UserServiceImpl=======");}
}@Slf4j
@Service("userServiceEs")
public class UserServiceEs implements UserService {@Overridepublic void show() {log.info("=======UserService-----UserServiceEs=======");}
}

@RestController
public class TestController {@Autowired@Qualifier("userServiceImpl")private UserService userService;//通过名称@Resource(name="userServiceEs")private UserService userServiceES;@GetMapping("/hello")public String test() {userService.show();userServiceES.show();return "hello ma!!!";}
}执行结果
=======UserService-----UserServiceImpl=======
=======UserService-----UserServiceEs=======

3、@configuration和@component之间的区别

3.1、@configuration和@component之间的区别

@Component注解的范围最广，所有类都可以注解，但是@Configuration注解一般注解在这样的类上：这个类里面有@Value注解的成员变量和@Bean注解的方法，就是一个配置类。

@Configuration 中所有带 @Bean 注解的方法都会被动态代理，因此调用该方法返回的都是同一个实例

@Data
@Service
public class Org {
}@Data
public class Unit {private Org org;public Unit(Org org) {this.org = org;}
}@Configuration
public class MyBeanConfig {@Beanpublic Org orgBean() {return new Org();}@Beanpublic Unit unitBean() {return new Unit(orgBean());}
}@SpringBootTest
class DemoApplicationTests {@Testvoid test() {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MyBeanConfig.class);Org orgBean = (Org) applicationContext.getBean("orgBean");Unit unitBean = (Unit) applicationContext.getBean("unitBean");System.out.println(orgBean==unitBean.getOrg());}
}执行结果
true

@Data
@Service
public class Org {
}@Data
public class Unit {private Org org;public Unit(Org org) {this.org = org;}
}@Component
public class MyBeanConfig {@Beanpublic Org orgBean() {return new Org();}@Beanpublic Unit unitBean() {return new Unit(orgBean());}
}@SpringBootTest
class DemoApplicationTests {@Testvoid test() {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MyBeanConfig.class);Org orgBean = (Org) applicationContext.getBean("orgBean");Unit unitBean = (Unit) applicationContext.getBean("unitBean");System.out.println(orgBean==unitBean.getOrg());}
}执行结果
false

4、Scope

基本作用域（singleton，prototype），web作用域（request，session，globalsession）

@Scope(value=ConfigurableBeanFactory.SCOPE_PROTOTYPE)这个是说在每次注入的时候回自动创建一个新的bean实例

@Scope(value=ConfigurableBeanFactory.SCOPE_SINGLETON)单例模式，在整个应用中只能创建一个实例

@Scope(value=WebApplicationContext.SCOPE_GLOBAL_SESSION)全局session中的一般不常用

@Scope(value=WebApplicationContext.SCOPE_APPLICATION)在一个web应用中只创建一个实例

@Scope(value=WebApplicationContext.SCOPE_REQUEST)在一个请求中创建一个实例

@Scope(value=WebApplicationContext.SCOPE_SESSION)每次创建一个会话中创建一个实例

二、ApplicationContext的三个常用实现类

1、ClassPathXmlApplicationContext

可以加载类路径下的配置文件，不在的话加载不了

ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml");
Hello hello = (Hello) act.getBean("hello");
hello.show();

2、FileSystemXmlApplicationContext

可以加载磁盘任意路径下的配置文件（必须有访问权限）

ApplicationContext act = new FileSystemXmlApplicationContext("D:/javaWorkSpace/spring2/src/applicationContext.xml");
person persons = (person) act.getBean("persons");
persons.show();

6.3、AnnotationConfigApplicationContext

 用于读取注解创建容器的

AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(DemoApplication.class);UserService bean = applicationContext.getBean(UserService.class);bean.show();