Springboot学习笔记（2）——依赖注入之一（注解配置）

控制反转（IoC）是通过依赖注入实现的。

依赖注入的步骤：

1、编写并声明Bean

package com.red.demo.ioc;

import org.springframework.stereotype.Service;

@Service //1
public class Screen {
  public String display(){
    return "我命由我不由天！";
  }
}

声明Bean的注解有：@Component、@Service、@Controller和@Repository等，它们在功能上没有区别，在这里都可以使用，只是它们具有各自的字面意义。

2、编写使用该Bean的类（被注入的类）

package com.red.demo.ioc;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class Cinema {
  @Autowired //2
  Screen nezha;
  public String playMovie(){
    return nezha.display();
  }
}

注入Bean的注解有：@Autowired、@Inject和@Resource。

其中，@Autowired为Spring提供的注解、@Inject（JSR-330）和@Resouce（JSR-250）都是Java提供的注解。

3、编写配置类

package com.red.demo.ioc;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration //3
@ComponentScan("com.tiger.demo.ioc") //4
public class MovieConfig {

}

4、运行

package com.red.demo;

import com.tiger.demo.ioc.Cinema;
import com.tiger.demo.ioc.MovieConfig;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class DemoApplication {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(MovieConfig.class);
        Cinema cinema = context.getBean(Cinema.class);
        System.out.println(cinema.playMovie());
        context.close();
    }

运行打印的日志：

10:57:03.238 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@1363fb3
10:57:03.262 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalConfigurationAnnotationProcessor'
10:57:03.368 [main] DEBUG org.springframework.context.annotation.ClassPathBeanDefinitionScanner - Identified candidate component class: file [D:IdeaProjectsdemo	argetclassescom
eddemoiocCinema.class]
10:57:03.369 [main] DEBUG org.springframework.context.annotation.ClassPathBeanDefinitionScanner - Identified candidate component class: file [D:IdeaProjectsdemo	argetclassescom
eddemoiocScreen.class]
10:57:03.485 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerProcessor'
10:57:03.488 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerFactory'
10:57:03.491 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalAutowiredAnnotationProcessor'
10:57:03.491 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalCommonAnnotationProcessor'
10:57:03.525 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'movieConfig'
10:57:03.538 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'cinema'
10:57:03.550 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'screen'
我命由我不由天！
10:57:03.582 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@1363fb3, started on Sun Aug 11 10:57:03 CST 2019