1. 注解开发定义Bean对象

目的：xml配置Bean对象有些繁琐，使用注解简化Bean对象的定义

1.1 在applicationContext.xml中开启Spring注解包扫描

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       
       xmlns:context="http://www.springframework.org/schema/context"
       
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
           http://www.springframework.org/schema/beans 
           http://www.springframework.org/schema/beans/spring-beans.xsd
           
                           
           http://www.springframework.org/schema/context                  
           http://www.springframework.org/schema/context/spring-context.xsd">
	 <!--扫描com.lin包及其子包下的类中注解-->
    <context:component-scan base-package="com.lin"/>
</beans>

1.2 在类上使用@Component注解定义Bean。

BookDaoImpl

package com.lin.dao.daoimpl;

import com.lin.dao.BookDao;
import org.springframework.stereotype.Component;

@Component("bookDao")
public class BookDaoImpl implements BookDao {

    public void save() {
        System.out.println("数据层的save");
    }
}

BookServiceImpl

package com.lin.service.serviceimpl;

import com.lin.dao.BookDao;
import com.lin.service.BookService;
import org.springframework.stereotype.Component;

@Component
public class BookServiceImpl implements BookService {

    private BookDao bookDao;

    public void setBookDao(BookDao bookDao) {
        this.bookDao = bookDao;
    }

    public void save() {
        bookDao.save();
        System.out.println("业务层的save");
    }
}

补充说明：如果@Component注解没有使用参数指定Bean的名称，那么类名首字母小写就是Bean在IOC容器中的默认名称。例如：BookServiceImpl对象在IOC容器中的名称是bookServiceImpl。

1.3 在测试类中获取Bean对象

package com.lin.app;

import com.lin.dao.BookDao;
import com.lin.service.BookService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Application {
    public static void main(String[] args) {
        //1.获取spring容器,加载配置文件
        ApplicationContext springContext = new ClassPathXmlApplicationContext("applicationContext.xml");

        //按id并指定类型获取bean
        BookDao bookDao = springContext.getBean("bookDao", BookDao.class);
        bookDao.save();
        //按类型获取bean
        BookService bookService = springContext.getBean(BookService.class);
         System.out.println(bookService); 
    }
}

在测试类中不要调用bookService的save方法，因为还没有给BookServiceImpl中的bookDao赋值，调用bookService的save方法会出现空指针异常。

1.4 运行结果

2. 纯注解开发模式

2.1 纯注解开发模式介绍

• Spring3.0开启了纯注解开发模式，使用Java类替代配置文件，开启了Spring快速开发赛道
• Java类代替Spring核心配置文件

2.2 代码演示

2.2.1 定义配置类代替配置文件

package com.lin.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
//声明当前类为Spring配置类
@Configuration
//Spring注解扫描，相当于<context:component-scan base-package="com.lin"/>
@ComponentScan("com.lin")
public class SpringConfig {
}

2.2.2 在测试类中加载配置类，获取Bean对象并使用

public class AppForAnnotation {
    public static void main(String[] args) {
        //AnnotationConfigApplicationContext加载Spring配置类初始化Spring容器
        ApplicationContext ctx = new AnnotationConfigApplicationContext(SpringConfig.class);
        BookDao bookDao = (BookDao) ctx.getBean("bookDao");
        System.out.println(bookDao);
        //按类型获取bean
        BookService bookService = ctx.getBean(BookService.class);
        System.out.println(bookService);
    }
}