Question

我学习斯普林斯并在学习@Autowiring时遇到@Qualifier。我已经宣布了一个限定符，但仍然会抛出异常。

以下是我的代码

Spring.xml：

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-3.0.xsd">


    <bean id="pointA" class="org.xyz.practice.Point">
        <qualifier value="myCircle" />
        <constructor-arg index="0" value="${pointA.pointX}"></constructor-arg>
        <constructor-arg index="1" value="${pointA.pointY}"></constructor-arg>
    </bean>

    <bean id="pointB" class="org.xyz.practice.Point">
        <constructor-arg index="0" value="${pointA.pointX}"></constructor-arg>
        <constructor-arg index="1" value="${pointA.pointY}"></constructor-arg>
    </bean>

    <bean
        class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations" value="configurations.properties"></property>
    </bean>



    <bean id="circle" class="org.xyz.practice.Circle">

    </bean>

    <bean
        class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />


</beans>

Circle.java：

package org.xyz.practice;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;

public class Circle implements Shape {

    private Point center;

    public Point getCenter() {
        return center;
    }

    @Autowired
    @Qualifier("myCircle")
    public void setCenter(Point center) {
        this.center = center;
    }

    @Override
    public void draw() {
        System.out.println("Drawing a circle...");
        System.out.println("Circle point si (" + center.getX() + " , " + center.getY() + ")");
    }

}

MainClass：

package org.xyz.practice;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class DrawingApp {

    public static void main(String[] args) {

        ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
        Shape shape = (Shape) context.getBean("circle");
        shape.draw();
    }

}

例外：

WARNING: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'circle': Unsatisfied dependency expressed through method 'setCenter' parameter 0: No qualifying bean of type [org.xyz.practice.Point] is defined: expected single matching bean but found 2: pointA,pointB; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [org.xyz.practice.Point] is defined: expected single matching bean but found 2: pointA,pointB
Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'circle': Unsatisfied dependency expressed through method 'setCenter' parameter 0: No qualifying bean of type [org.xyz.practice.Point] is defined: expected single matching bean but found 2: pointA,pointB; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [org.xyz.practice.Point] is defined: expected single matching bean but found 2: pointA,pointB
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:647)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:349)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1214)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:775)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:861)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:541)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
    at org.xyz.practice.DrawingApp.main(DrawingApp.java:10)
Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [org.xyz.practice.Point] is defined: expected single matching bean but found 2: pointA,pointB
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:172)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1064)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1018)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:639)
    ... 15 more

请不要将此标记为@Resource（相关）问题的副本，我想逐步进行。

Answer 1

通过向Circle bean添加center属性，通过xml完成Spring上下文配置。

<bean id="circle" class="org.xyz.practice.Circle">
    <property name="center" class="package.Point"/>
</bean>

您也没有使用@Annotation配置，尽量不要混合使用xml和@Annotation配置。如果要使用该配置，请将组件扫描添加到applicationContext.xml。

<context:component-scan base-package="base.package.to.scan" />

Answer 2

将限定符放在参数上：

@Autowired
public void setCenter(@Qualifier("myCircle") Point center) {
    this.center = center;
}

弹簧限定符错误

2 个答案: