Spring使用注解進(jìn)行引用類型的自動(dòng)裝配逐步分析

更新時(shí)間：2023年03月06日 08:44:28 作者：拉不拉斯

自動(dòng)裝配是springboot的核心，一般提到自動(dòng)裝配就會(huì)和springboot聯(lián)系在一起。實(shí)際上Spring Framework早就實(shí)現(xiàn)了這個(gè)功能。Spring Boot只是在其基礎(chǔ)上，通過SPI的方式，做了進(jìn)一步優(yōu)化

一.案例分級(jí)

簡(jiǎn)單解析:配置類替代以前的配置文件，實(shí)體類提供對(duì)象，業(yè)務(wù)類中有實(shí)體類的引用對(duì)象，在業(yè)務(wù)層中實(shí)現(xiàn)引用類的自動(dòng)裝配。

二.各層代碼及詳細(xì)解析

配置類:(關(guān)于配置類中兩個(gè)注解的解釋可以參考前面文章)

package com.itheima.config;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration //設(shè)置為配置類
@ComponentScan("com.itheima") //在com.otheima這個(gè)包下掃描bean對(duì)象
public class SpringConfig {
}

實(shí)體類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  //注解注冊(cè)bean
public class BookDaoImpl implements BookDao {
    public void save() {
        System.out.println("book dao save ...");
    }
    }

實(shí)體接口BookDao:

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

業(yè)務(wù)類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 {
    @Autowired
    private BookDao bookDao;
    public void save() {
        System.out.println("book service save....");
        bookDao.save();
    }
}

@Service:注冊(cè)bean對(duì)象，在執(zhí)行類中使用getBean()方法獲取.

@Autowired:進(jìn)行自動(dòng)裝配，如果沒有此句話，將會(huì)出現(xiàn)以下錯(cuò)誤運(yùn)行結(jié)果:

業(yè)務(wù)接口BookService:

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

執(zhí)行類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();
    }
}