首页 计算机学科 java spring 代码案例

如果我们按原始的来就会报错如下:

image_2023-02-25-09-42-09

找不到 save 报了空指针

  • 使用依赖注入：自动装配 解决问题

  • @Autowired: 按类型装配 Spring bean

@SuppressWarnings("all")
@Service("bookService")
public class BookServiceImpl implements BookService {
    @Autowired
    private BookDao bookDao;
    public void setBookDao(BookDao d){
        this.bookDao = d;
    }
    public void save(){
        System.out.println("BookServiceImpl save rning...");
        bookDao.save();
    }
}

在 private BookDao bookDao; 上加上注解:@Autowired 注解来进行自动装配

  • 测试代码
public void test(){
        ApplicationContext c = new AnnotationConfigApplicationContext(SpringConfig.class);
        BookService service = c.getBean("bookService",BookService.class);
        service.save();
    }

Run Result

image_2023-02-25-09-46-33

  • 可以将 setter 方法给去掉，因为它暴力反射已经帮我们做了
@SuppressWarnings("all")
@Service("bookService")
public class BookServiceImpl implements BookService {
    @Autowired
    private BookDao bookDao;
    public void save(){
        System.out.println("BookServiceImpl save rning...");
        bookDao.save();
    }
}
Run Result
image_2023-02-25-10-03-22
问题
  • 如果有两个相同的数据层 (Dao), 那么类型就会不一致就会报错如下
  • BookDaoImpl
@SuppressWarnings("all")
@Repository("bookDao")
public class BookDaoImpl implements BookDao {
    public void save(){
        System.out.println("BookDaoImpl save rning...");
    }
}
  • BookDaoImpl1
@SuppressWarnings("all")
@Repository("bookDao")
public class BookDaoImpl1 implements BookDao {
    public void save(){
        System.out.println("BookDaoImpl save rning...");
    }
}
  • BookServiceImpl 自动装配类绑定 BookDao 接口类
    • 有两个 BookDao 的实现类此时数据就不唯一了，Run 后报错
@SuppressWarnings("all")
@Service("bookService")
public class BookServiceImpl implements BookService {
    @Autowired
    private BookDao bookDao;
    public void save(){
        System.out.println("BookServiceImpl save rning...");
        bookDao.save();
    }
}
image_2023-02-25-10-09-14
  • 解决方式
按名称装配
给 @Repository 注解配置 bean 设置名称
  • BookDaoImpl
@SuppressWarnings("all")
@Repository("bookDao")
public class BookDaoImpl implements BookDao {
    public void save(){
        System.out.println("BookDaoImpl save rning...");
    }
}
  • BookDaoImpl1
@SuppressWarnings("all")
@Repository("bookDao1")
public class BookDaoImpl1 implements BookDao {
    public void save(){
        System.out.println("BookDaoImpl save rning...  1");
    }
}
  • BookServiceImpl
@SuppressWarnings("all")
@Service("bookService")
public class BookServiceImpl implements BookService {
    @Autowired
    private BookDao bookDao;
    public void save(){
        System.out.println("BookServiceImpl save rning...");
        bookDao.save();
    }
}
  • 问题：有两个那么会先执行哪一个呢
    • 按顺序执行
Run Result
image_2023-02-25-10-22-16
将注解配置 bean 的名称换下顺序
  • BookDaoImpl
@Repository("bookDao1")
public class BookDaoImpl implements BookDao {
  • BookDaoImpl1
@Repository("bookDao")
public class BookDaoImpl1 implements BookDao {
Run Result
image_2023-02-25-10-24-12