Question

Here is my xml config:

<bean id="diameterClient" class="com.rory.ptspsim.diameterclient.DiameterClient" scope="singleton" init-method="start">
    <constructor-arg index="0"><value>${pcca.host}</value></constructor-arg>      
    <constructor-arg index="1"><value>${pcca.port}</value></constructor-arg>      
    <constructor-arg index="2" value="com.rory.djgx.message"/>
    <constructor-arg index="3" value="com.rory.djgx.avp"/> 
    <constructor-arg index="4">
    <list>
        <ref bean="asrHandler"/>
        <ref bean="aaaHandler"/>
        <ref bean="ceaHandler"/>
        <ref bean="dwaHandler"/>
        <ref bean="staHandler"/>
    </list>
    </constructor-arg> 
</bean>

<bean id="asrHandler" class="com.rory.ptspsim.messagereceivers.ASRHandler"/>
<bean id="aaaHandler" class="com.rory.ptspsim.messagereceivers.AAAHandler"/>
<bean id="ceaHandler" class="com.rory.ptspsim.messagereceivers.CEAHandler"/>
<bean id="dwaHandler" class="com.rory.ptspsim.messagereceivers.DWAHandler"/>
<bean id="staHandler" class="com.rory.ptspsim.messagereceivers.STAHandler"/>

And here is the start of the ASRHandler class:

public class ASRHandler implements DiameterMessageHandler
{   
    @Autowired
    private DiameterClient diameterClient;

Does anyone have any idea why this isnt working? I realise the the handler class and the DiameterClient class have a dependancy on each other, but I though Spring took care of that.

Here is the message from the log:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name ‘diameterClient’ defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Cannot resolve reference to bean ‘asrHandler’ while setting constructor argument with key [0]; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name ‘asrHandler’: Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name ‘diameterClient’: Requested bean is currently in creation: Is there an unresolvable circular reference?

Thanks!

Answer 1

This is most certainly a circular dependency. You should be seeing a BeanCurrentlyInCreationException thrown by Spring.

Beans cannot be referenced when they are being instantiated already. The issue is that you are using constructor injection to create your beans.

I see two things that should be able to fix this.

1. Based on the package name of DiameterClient I am assuming it is a class that you are in control of. I would recommend autowiring all dependencies of that class as you have with your xxxHandler classes. You should even be able to @Autowired a List<DiameterMessageHandler>, and Spring will load all beans that implement that interface into the list.
2. Use property based injection on your beans (instead of the constructor-arg element, use the property element).

EDIT:

If you have your files looks something like this:

<bean id="diameterClient" class="com.rory.ptspsim.diameterclient.DiameterClient" scope="singleton" init-method="start"/>

<bean id="asrHandler" class="com.rory.ptspsim.messagereceivers.ASRHandler"/>
<bean id="aaaHandler" class="com.rory.ptspsim.messagereceivers.AAAHandler"/>
<bean id="ceaHandler" class="com.rory.ptspsim.messagereceivers.CEAHandler"/>
<bean id="dwaHandler" class="com.rory.ptspsim.messagereceivers.DWAHandler"/>
<bean id="staHandler" class="com.rory.ptspsim.messagereceivers.STAHandler"/>

and this:

public class DiameterClient {
    @Autowired
    private List<DiameterMessageHandler> handlers;

    @Value("${pcca.host}")
    private String host;

    @Value("${pcca.port}")
    private int port; // or String...

    // I don't know what these other two would be...if they are autowired, or just values you would populate...
    private String somePackage;

    private String anotherPackage;

    // methods go here...
}

then the List<DiameterMessageHandler> would contain the 5 beans you have defined under your diameterClient bean in your xml. If order is important, you may need to specify them in your context in a specific order, but otherwise it should just work.

You could even take this further and annotate your classes with a Stereotype annotation (@Component most likely) and do a context:component-scan on the packages that contain these classes. That would mean even less xml declaration.