java - ApplicationContextAware 在单例对象中注入(inject)原型(prototype)对象

Question

我正在尝试在单例类中注入(inject)原型(prototype)对象..

public class Triangle implements ApplicationContextAware{
private Point pointA;
private ApplicationContext context=null;
Point point=(Point)context.getBean("pointA",Point.class);
public void draw(){
    System.out.println("The prototype point A is ("+point.getX()+","+point.getY()+")");
}
@Override
public void setApplicationContext(ApplicationContext context)
    throws BeansException {
this.context=context;

}
}

我创建了一个 Point java 文件，坐标为 x 和 y..

当我尝试编译上面的代码时，出现以下错误

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'triangle' defined in class path resource [Spring.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.david.shape.Triangle]: Constructor threw exception; nested exception is java.lang.NullPointerException

Answer 1

private ApplicationContext context=null;
Point point=(Point)context.getBean("pointA",Point.class);

您正在对 context 调用 getBean()，这显然是 null。

只有在 Triangle bean 构造完毕并且 Spring 调用其 setApplicationContext() 方法之后，Spring 才会初始化上下文。只有这样，您才能在上下文上调用 getBean()。

顺便说一句，你在这里没有进行依赖注入(inject)。您正在执行依赖项查找，这正是 Spring 等依赖项注入(inject)框架所要避免的。要注入(inject)您的观点，只需执行

public class Triangle {

    private Point pointA;

    @Autowired
    public Triangle(@Qualifier("pointA") Point pointA) {
        this.pointA = pointA;
    }

    ...
}