Spring Bean的声明方式

一、环境说明

1. 项目结构

   

2. StudentService

   package com.cookie.service;
   
   /**
    * @author cxq
    * @version 1.0
    * @date 2020/7/14 9:18
    * @desc
    */
   public interface StudentService {
   
       void add();
   }
   
   

3. StudentServiceImpl

   package com.cookie.service.impl;
   
   import com.cookie.service.StudentService;
   import org.springframework.stereotype.Component;
   
   /**
    * @author cxq
    * @version 1.0
    * @date 2020/7/14 9:20
    * @desc
    */
   public class StudentServiceImpl implements StudentService {
   
       public void add() {
           System.out.println(" add student ... ");
       }
   }
   
   

4. applicationContext.xml核心配置文件

   <?xml version="1.0" encoding="UTF-8"?>
   <beans xmlns="http://www.springframework.org/schema/beans"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xmlns:context="http://www.springframework.org/schema/context"
          xsi:schemaLocation="http://www.springframework.org/schema/beans
           https://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
   
   </beans>
   

二、XML

1. 以bean的方式在核心配置文件中声明

   <!--
         xml声明
           id : bean的唯一标识
           class：bean所在的Java类的全类名
       -->
   <bean id="studentService" class="com.cookie.service.impl.StudentServiceImpl" />
   

2. 通过ClassPathXmlApplicationContext读取配置文件

   /**
        * 基于xml声明bean
        */
       @Test
       public void method1(){
           // 1.获取容器：读取配置文件
           ApplicationContext applicationContext
                   = new ClassPathXmlApplicationContext("applicationContext.xml");
   
           // 2.获取bean
           StudentService studentService = (StudentService) applicationContext.getBean("studentService");
   
           // 3.调用对应的方法
           studentService.add();
       }
   

三、注解扫描

1. 在核心配置文件中加入要扫描的类

   <!--
       2.注解扫描
           base-package ：类所在的包
       -->
   <context:component-scan base-package="com.cookie.service" />
   

2. 在对应类上加上@Component将该类放入IOC容器中，并起一个别名

   @Component("studentService")
   public class StudentServiceImpl implements StudentService {
   
       public void add() {
           System.out.println(" add student ... ");
       }
   }
   

3. 通过ClassPathXmlApplicationContext读取配置文件

   /**
        * 2.注解扫描
        *
        */
       @Test
       public void method2(){
           // 1.获取容器：读取配置文件
           ApplicationContext applicationContext
                   = new ClassPathXmlApplicationContext("applicationContext.xml");
   
           // 2.获取bean
           StudentService studentService = (StudentService) applicationContext.getBean("studentService");
   
           // 3.调用对应的方法
           studentService.add();
       }
   
   

四、Java类

1. 创建一个java类CommonConfig

   package com.cookie;
   
   import com.cookie.service.StudentService;
   import com.cookie.service.impl.StudentServiceImpl;
   import org.springframework.context.annotation.Bean;
   import org.springframework.context.annotation.Configuration;
   
   /**
    * @author cxq
    * @version 1.0
    * @date 2020/7/14 10:15
    * @desc
    */
   @Configuration // 声明这是一个配置类
   public class CommonConfig {
   
       @Bean	// 声明bean
       public StudentService studentService(){
           return  new StudentServiceImpl();
       }
   }
   
   

2. 通过AnnotationConfigApplicationContext读取该java配置类

    /**
        * 3.基于java类
        *
        */
       @Test
       public void method3(){
   
           ApplicationContext applicationContext
                   = new AnnotationConfigApplicationContext(CommonConfig.class);
   
           StudentService studentService = (StudentService) applicationContext.getBean("studentService");
   
           studentService.add();
       }