Injecting a named String using CDI

Question

I want to have a configuration parameter injected this way:

public class MyManagedBean {
    @Inject
    public MyManagedBean(@Named("user") String user){
        ....

    }
}

So I tried to implement a producer method this way:

@ApplicationScoped
public class MyConfiguration {
    private Properties loadProperties() {
        Properties properties = new Properties();
        try {
            properties.load(getClass().getResourceAsStream(
                    "user.properties"));
        } catch (IOException e) {
            throw new RuntimeException();
        }
        return properties;
    }

    @Produces
    @Named("user")
    String getUser() {
        return loadProperties().getProperty("user");
    }
}

I have other bean defined this way:

public class OtherManagedBean {
    @Inject
    public OtherManagedBean(MyManagedBean myManagedBean){
        ....

    }
}

However, I'm having this exception when I try to deploy it:

INFO: WEB0671: Loading application [example-ear#example-war.war] at [example]
SEVERE: Exception while loading the app
SEVERE: Exception while loading the app : WELD-001410 The injection point [parameter 1] of [constructor] @Inject public com.example.OtherManagedBean(MyManagedBean) has non-proxyable dependencies
org.jboss.weld.exceptions.UnproxyableResolutionException: WELD-001410 The injection point [parameter 1] of [constructor] @Inject public com.example.OtherManagedBean(MyManagedBean) has non-proxyable dependencies
    at org.jboss.weld.bootstrap.Validator.validateInjectionPoint(Validator.java:317)
    at org.jboss.weld.bootstrap.Validator.validateBean(Validator.java:139)
    at org.jboss.weld.bootstrap.Validator.validateRIBean(Validator.java:162)
    at org.jboss.weld.bootstrap.Validator.validateBeans(Validator.java:385)
    at org.jboss.weld.bootstrap.Validator.validateDeployment(Validator.java:371)
    at org.jboss.weld.bootstrap.WeldBootstrap.validateBeans(WeldBootstrap.java:390)
    at org.glassfish.weld.WeldDeployer.event(WeldDeployer.java:190)
    at org.glassfish.kernel.event.EventsImpl.send(EventsImpl.java:128)
    at org.glassfish.internal.data.ApplicationInfo.start(ApplicationInfo.java:298)
    at com.sun.enterprise.v3.server.ApplicationLifecycle.deploy(ApplicationLifecycle.java:461)
    at com.sun.enterprise.v3.server.ApplicationLifecycle.deploy(ApplicationLifecycle.java:240)
    at org.glassfish.deployment.admin.DeployCommand.execute(DeployCommand.java:370)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl$1.execute(CommandRunnerImpl.java:355)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl.doCommand(CommandRunnerImpl.java:370)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl.doCommand(CommandRunnerImpl.java:1067)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl.access$1200(CommandRunnerImpl.java:96)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl$ExecutionContext.execute(CommandRunnerImpl.java:1247)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl$ExecutionContext.execute(CommandRunnerImpl.java:1235)
    at com.sun.enterprise.v3.admin.AdminAdapter.doCommand(AdminAdapter.java:465)
    at com.sun.enterprise.v3.admin.AdminAdapter.service(AdminAdapter.java:222)
    at com.sun.grizzly.tcp.http11.GrizzlyAdapter.service(GrizzlyAdapter.java:168)
    at com.sun.enterprise.v3.server.HK2Dispatcher.dispath(HK2Dispatcher.java:117)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:234)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:822)
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:719)
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1013)
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:225)
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
    at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
    at java.lang.Thread.run(Thread.java:662)

Any idea?

Thanks.

Answer 1

It looks like you need a default (no-arg) constructor for your MyManagedBean to make it proxyable. I am not really sure about why it is needed, since MyManagedBean is a @Dependent bean and so is not proxied AFAIK; I do not know even why a proxyable bean needs a default constructor, to be honest This seems to be an implementation detail or a little point from CDI specification that was ignored. Anyway, I bet it can make a good new question :)

EDIT: I discovered why a proxyable bean needs a default construction. It is no mistery, actually: since the proxy of a bean is a subclass of the same bean, the proxy needs to call a super() constructor in its own construction. If it has no non-private default constructor, it does not know which constructor to call. One can even imagine a scenario where the injected constructor is called to create the proxy, but I do not know which kind of complexity it can add to a CDI implementation; it may not be so easy to do...