Spring中的三种依赖注入方式
- Field Injection ：@Autowired注解的一大使用场景就是Field Injection
- Constructor Injection ：构造器注入，是我们日常最为推荐的一种使用方式Setter Injection：
- Setter Injection也会用到@Autowired注解，但使用方式与Field Injection有所不同，Field Injection是用在成员变量上，而Setter Injection的时候，是用在成员变量的Setter函数上
// Field Injection
@Service("uploadService")
public class UploadServiceImpl extends ServiceImpl<UploadDao, UploadEntity> implements UploadService {
@Autowired
private UploadDao uploadDao;
}
// Constructor Injection
@Service("uploadService")
public class UploadServiceImpl extends ServiceImpl<UploadDao, UploadEntity> implements UploadService {
private UploadDao uploadDao;
UploadServiceImpl(UploadDao uploadDao){
this.uploadDao = uploadDao;
}
}
// Setter Injection
@Service("uploadService")
public class UploadServiceImpl extends ServiceImpl<UploadDao, UploadEntity> implements UploadService {
private UploadDao uploadDao;
@Autowired
public void setUploadDao(UploadDao uploadDao){
this.uploadDao =uploadDao
}
}
1.是否进行循环依赖检测
- Field Injection：不检测
- Constructor Injection：自动检测
- Setter Injection：不检测
可能遇到的问题
循环依赖报错: 当服务A需要用到服务B时，并且服务B又需要用到服务A时，Spring在初始化创建Bean时，不知道应该先创建哪一个，就会出现该报错。
This is often the result of over-eager type matching - consider using 'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example
class ServerA{
@Autowired
private ServerB b;
}
class ServerB{
@Autowired
private ServerA a;
}
如果使用构造方式注入，能够精准的提醒你是哪两个类产生了循环依赖 .异常报错信息能够迅速定位问题:
循环报错解决办法是使用 @Lazy注解 ，对任意一个需要被注入Bean添加该注解，表示延迟创建即可。
class ServerA{
@Autowired
@Lazy
private ServerB b;
}
class ServerB{
@Autowired
@Lazy
private ServerA a;
}
以上就是Java详细讲解依赖注入的方式的详细内容，更多关于Java依赖注入的资料请关注Devmax其它相关文章！