Spring入门案例三:注解进行引用类型的自动装配

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一.案例分级

简单解析:配置类替代以前的配置文件，实体类提供对象，业务类中有实体类的引用对象，在业务层中实现引用类的自动装配。

二.各层代码及详细解析

配置类:(关于配置类中两个注解的解释可以参考前面文章)

package com.itheima.config;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration //设置为配置类
@ComponentScan("com.itheima") //在com.otheima这个包下扫描bean对象
public class SpringConfig {
}

实体类BookDaoImpl:

package com.itheima.dao.impl;
import com.itheima.dao.BookDao;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Repository;
@Repository  //注解注册bean
public class BookDaoImpl implements BookDao {public void save() {System.out.println("book dao save ...");}}

实体接口BookDao:

package com.itheima.dao;
public interface BookDao {public void save();
}

业务类BookServiceImol:

package com.itheima.service.impl;import com.itheima.dao.BookDao;
import com.itheima.service.BookService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class BookServiceImol implements BookService {@Autowiredprivate BookDao bookDao;public void save() {System.out.println("book service save....");bookDao.save();}
}

@Service:注册bean对象，在执行类中使用getBean()方法获取.
@Autowired:进行自动装配，如果没有此句话，将会出现以下错误运行结果:

业务接口BookService:

package com.itheima.service;
public interface BookService {public void save();
}

执行类App3:

package com.itheima;
import com.itheima.config.SpringConfig;
import com.itheima.dao.BookDao;
import com.itheima.service.BookService;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import java.awt.print.Book;
public class App3 {public static void main(String[] args) {AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(SpringConfig.class);BookService service=ctx.getBean(BookService.class);service.save();}
}

三.自动装配成功正确执行结果

        后续文章:使用注解进行简单类型的自动装配,关注我持续更新，麻烦点个赞啦！！！