java - Spring bean创建错误

Question

所以我一直在关注 Spring 文档，特别是这一部分，

http://static.springsource.org/spring/docs/current/spring-framework-reference/html/beans.html#beans-factory-collaborators依赖注入(inject)，但每当我的代码运行时，我都会收到有关 bean 创建的错误。

这是我尝试基于 ExampleBean 示例的部分代码，

public class TimeFeedHandler implements MessageListener {

    String msgID = null;

    TimeBayeuxService timeBayeuxService;

        public void setTimeBayeuxService(TimeBayeuxService timeBayeuxService) {
            this.timeBayeuxService = timeBayeuxService;
        }

我的 Spring XML 文件如下所示，

<!-- A POJO that implements the JMS message listener -->

<bean id="timeFeedHandler" class="com.example.streaming.time.TimeFeedHandler" >
<property name="timeBayeuxService" ref="timeBayeuxService"> </property>
</bean>

我得到的错误是，

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'timeFeedHandler' defined in URL....

你知道我做错了什么或者为什么做错了吗？

编辑，这里是 TimeBayeuxService bean，

<!-- Time BayeuxServices -->

<bean id="timeBayeuxService" class="com.example.streaming.time.TimeBayeuxService" lazy-init="true">
    <constructor-arg><ref bean="common.bayeux" /></constructor-arg>
    <property name="timeBean" ref="time.time" />
</bean>

这里有更多错误。 STS 的完整错误日志太长了。我觉得我没有正确引用 TimeBayeuxService bean，但从逻辑上讲，我似乎看不出我做错了什么。

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'timeFeedHandler' defined in URL [file:/Users/nullpoint/applicationContext.xml]: Cannot resolve reference to bean 'timeBayeuxService' while setting bean property 'timeFeedHandler'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'timeBayeuxService' defined in URL [file:/Users/nullpoint/applicationContext.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.example.streaming.time.TimeBayeuxService]: Constructor threw exception; nested exception is java.lang.NullPointerException
at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:328)

这是 TimeBayeuxService 类的一部分

public class TimeBayeuxService {

private Bayeux bayeux;
private static StreamingTimeLogGatherer logGatherer;
String testMsgTS = "This is a test message from the original service";

public TimeBayeuxService(Bayeux bayeux) extends SomeBayeuxService{
    super(bayeux, TimeBayeuxService.class.getName());

    this.bayeux = bayeux;
    final Bayeux fbayeux = bayeux;

    this.logGatherer = logGatherer;
    LogServlet.addLogGatherer(logGatherer);

    startThread(fbayeux, testMsgTS, true);

}

Answer 1

timeFeedHandler 依赖于 timeBayeuxService。由于NullPointerException，它无法初始化timeBayeuxService，因此spring无法注入(inject)bean。

根据错误信息，在com.example.streaming.time.TimeBayeuxService的构造函数中发生了NullPointerException。您如何创建common.bayeux bean？请粘贴 TimeBayeuxService 类的构造函数代码。是一个接口(interface)吗？然后你应该把实现类放在bean定义中。

NPE 可能出现的位置。如果没有完整的堆栈跟踪，我必须猜测以下代码行:

1. 它可能发生在父类(super class)的构造函数内。
2. 这两个方法:LogServlet.addLogGatherer(logGatherer); startThread(fbayeux, testMsgTS, true);