如果在Spring中將屬性設置為不同的Bean列表，則可以使用注釋創建Bean嗎？

Question

假設我有A，B，C，D，E類：

@Component
public class A {
}

@Component
public class B {
}

@Component
public class D {
}

@Component
public class E {
}

public class C {
private List myList;

public List getMyList() {
    return myList;
}

public void setMyList(List myList) {
    this.myList = myList;
}

}

這是我的應用程序上下文：

<?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"
xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="http://www.springframework.org/schema/beans 
http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd
    http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.2.xsd">


    <util:list id="myList1">
        <ref bean="a"/>
        <ref bean="b"/>
    </util:list>

    <util:list id="myList2">
        <ref bean="d"/>
        <ref bean="e"/>
    </util:list>

    <bean id="myFirstC" class="com.app.C">
        <property name="myList" ref="myList1"></property>
    </bean>

    <bean id="mySecondC" class="com.app.C">
        <property name="myList" ref="myList2"></property>
    </bean>

    <context:component-scan base-package="com.app"></context:component-scan>
    </beans>

是否可以使用C類內部的注釋來創建bean“ myFirstC”和“ mySecondC”？ 我試圖自動連接C類中的列表，然后使用@Bean批注創建bean並設置列表，但會出錯。

因此，我嘗試通過這種方式進行操作：

@Component
@Configuration
public class C {

private List myList;

@Autowired
@Qualifier("myList1")
private List myList1;

@Autowired
@Qualifier("myList2")
private List myList2;

@Bean
public C getNewCBean1() {
    C c = new C();
    c.setMyList(myList1);
    return c;
}

@Bean
public C getNewCBean2() {
    C c = new C();
    c.setMyList(myList2);
    return c;
}

但是得到這樣的錯誤：

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'c': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private java.util.List com.app.C.myList1; nested exception is org.springframework.beans.FatalBeanException: No element type declared for collection [java.util.List]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:288)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1116)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:519)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:458)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:295)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:292)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:626)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:932)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:479)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
    at com.app.Start.main(Start.java:9)
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private java.util.List com.app.C.myList1; nested exception is org.springframework.beans.FatalBeanException: No element type declared for collection [java.util.List]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:514)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:285)
    ... 13 more
Caused by: org.springframework.beans.FatalBeanException: No element type declared for collection [java.util.List]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:807)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:768)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:486)
    ... 15 more

我在文檔和論壇中找不到解決方案。 任何幫助將不勝感激。 謝謝

Answer 1

您的Java代碼與xml代碼根本沒有做相同的事情：

<util:list id="myList1">
    <ref bean="a"/>
    <ref bean="b"/>
</util:list>

<util:list id="myList2">
    <ref bean="d"/>
    <ref bean="e"/>
</util:list>

<bean id="myFirstC" class="com.app.C">
    <property name="myList" ref="myList1"></property>
</bean>

<bean id="mySecondC" class="com.app.C">
    <property name="myList" ref="myList2"></property>
</bean>

這定義了兩個bean myFirstC和mySecondC，分別包含bean a，b和d，e。 因此，在Java中，您需要兩個@Bean方法來創建相同的C bean：

 @Configuration
 public class Config {
     @Bean
     public C myFirstC(A a, B b) {
         return new C(Arrays.asList(a, b));
     }


     @Bean
     public C mySecondC(D d, E e) {
         return new C(Arrays.asList(d, e));
     }
 }