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问题:
一个对象为单例,但依赖的对象为多列对象,此时,该依赖的多列对象会变成单例
原因:
对象为单例,因此只实例化和初始化一次,因此该属性只被赋值一次,因此在该对象中,被依赖的对象始终为同一个对象
代码说明:
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>5.2.0.RELEASE</version>
</dependency>
</dependencies>
@ComponentScan(basePackages = {"com.wuhuafeng"})
public class AppConfig {
}
@Repository
@Scope(value = "prototype")
public class UserDao {
public void print(){
System.out.println("dao "+ this.hashCode());
}
}
@Service
public class UserService {
@Autowired
UserDao userDao;
public void print(){
System.out.println("userService "+ this.hashCode());
System.out.println("userDao "+ userDao.hashCode());
}
public void print1(){
System.out.println("userService "+ this.hashCode());
System.out.println("userDao "+ userDao.hashCode());
}
}
public class UserController {
public static void main(String[] args) {
AnnotationConfigApplicationContext AC = new AnnotationConfigApplicationContext(AppConfig.class);
UserService userService =(UserService) AC.getBean("userService");
userService.print();
userService.print1();
}
}
userService 1418385211
userDao 1282811396
userService 1418385211
userDao 1282811396
我们看到每次输出userDao的HashCode都是一样的,证明我们实际上并没有达到使用原型bean的目的。
解决方法:
方法一:
继承ApplicationContextAware
,使用applicationContext
从容器中获取依赖.
在bean A中引入ApplicationContext
每次调用方法时用上下文的getBean(name,class)
方法去重新获取bean B的实例
@Service
public class UserService implements ApplicationContextAware {
private ApplicationContext applicationContext;
public void print(){
UserDao userDao =(UserDao)applicationContext.getBean("userDao");
System.out.println("userService "+ this.hashCode());
System.out.println("userDao "+ userDao.hashCode());
}
public void print1(){
UserDao userDao =(UserDao)applicationContext.getBean("userDao");
System.out.println("userService "+ this.hashCode());
System.out.println("userDao "+ userDao.hashCode());
}
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
this.applicationContext =applicationContext;
}
}
userService 775931202
userDao 22069592
userService 775931202
userDao 1160003871
方法二(推荐使用):
使用@Lookup注解
@Service
public abstract class UserService {
@Lookup
protected abstract UserDao methodInject();
public void print(){
UserDao userDao = methodInject();
System.out.println("userService "+ this.hashCode());
System.out.println("userDao "+ userDao.hashCode());
}
public void print1(){
UserDao userDao = methodInject();
System.out.println("userService "+ this.hashCode());
System.out.println("userDao "+ userDao.hashCode());
}
}
使用这种抽象类的时候可以看出,在调用的时候使用的是他的CGLIb的动态代理类。
还有一种不用抽象方法可以写成(一样可以):
@Service
public class UserService {
@Lookup
protected UserDao methodInject(){
return null;
}
....
userService 210652080
userDao 1652149987
userService 210652080
userDao 1107730949