获取预实例化singletons错误

Question

我是Spring的新手。我在书中举了一个例子——《春天在行动2》。这个例子描述了如何编写bean，最后出现了错误。请帮我解决这个问题。这是代码：

package com.my.quest;
public interface Instrument {
    void play();
}
package com.my.quest;
public class Piano implements Instrument {
    public Piano(){}
    @Override
    public void play() {
        System.out.println("text");
    }
}
package com.my.quest;
public interface Performer {
    void perform ();
}
package com.my.quest;
public class Instrumentalist implements Performer {
    private Instrument inst;
    private String song;
    public Instrumentalist() {
    }
    void setSong(String song){
        this.song = song;
    }
    void setInstrument(Instrument inst){
        this.inst = inst;
    }
    @Override
    public void perform() {
        System.out.println("Playing " + song);
        inst.play();
    }
}

名为-config.xml的bean：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd">
    <bean id="kenny" class="com.my.quest.Instrumentalist"> 
    <property name="song" value="Cage The Elephant – Shake Me Down" />
    <property name="inst" ref="piano"/>
    </bean>
    <bean id="piano" class="com.my.quest.Piano">
    </bean>
</beans>

我已经用这种方式进行了测试，它正在发挥作用：

package com.my.quest;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class QuestStart {
    public static void main(String[] args) {    
        Instrument inst = new Piano();
        Instrumentalist in = new Instrumentalist();
        in.setInstrument(inst);
        in.setSong("Cage The Elephant – Shake Me Down");
        in.perform();
    }
}

结果：在控制台中键入消息->玩笼子大象-摇我一下：文本

但是如果我使用这个：

 package com.my.quest;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    public class QuestStart {
        public static void main(String[] args) {    
          ApplicationContext ctx = new ClassPathXmlApplicationContext("com/my/quest/config.xml");
          Performer p = (Performer)ctx.getBean("kenny");
          p.perform();  
        }
    }

我得到这个错误：

фев 08, 2015 11:25:51 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@7106e68e: startup date [Sun Feb 08 23:25:51 EET 2015]; root of context hierarchy
фев 08, 2015 11:25:52 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [com/my/quest/config.xml]
фев 08, 2015 11:25:52 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@256216b3: defining beans [kenny,piano]; root of factory hierarchy
фев 08, 2015 11:25:52 PM org.springframework.beans.factory.support.DefaultSingletonBeanRegistry destroySingletons
INFO: Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@256216b3: defining beans [kenny,piano]; root of factory hierarchy
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'kenny' defined in class path resource [com/my/quest/config.xml]: Error setting property values; nested exception is org.springframework.beans.NotWritablePropertyException: Invalid property 'song' of bean class [com.my.quest.Instrumentalist]: Bean property 'song' is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1361)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1086)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:295)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225)
    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:580)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:913)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:464)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
    at com.my.quest.QuestStart.main(QuestStart.java:19)
Caused by: org.springframework.beans.NotWritablePropertyException: Invalid property 'song' of bean class [com.my.quest.Instrumentalist]: Bean property 'song' is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?
    at org.springframework.beans.BeanWrapperImpl.setPropertyValue(BeanWrapperImpl.java:1031)
    at org.springframework.beans.BeanWrapperImpl.setPropertyValue(BeanWrapperImpl.java:899)
    at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:76)
    at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:58)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1358)
    ... 13 more

下载了几个JAR：

1. org.springframework.context和context.support-3.1.0.M2
2. org.springframework.asm-3.1.0.M2
3. org.springframework.expression-3.1.0.M2
4. org.springframework.beans-3.1.0.M2
5. org.springframework.core-3.1.0.M2
6. org.apache.common.logging

救命，让我看看我做错了什么。

Answer 1

Instrumentalist bean的setSong方法应该是public：

public void setSong(String song) {

通常也应该有一个匹配的getSong方法。