java - 使用 CDI 注入(inject)命名字符串

Question

我想以这种方式注入(inject)一个配置参数:

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

    }
}

所以我尝试以这种方式实现生产者方法:

@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");
    }
}

我以这种方式定义了其他 bean:

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

    }
}

但是，当我尝试部署它时出现此异常:

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)

有什么想法吗？

谢谢。

Answer 1

看起来你需要一个 default (no-arg) constructor为您的 MyManagedBean 使其可代理。我不太确定为什么需要它，因为 MyManagedBean 是一个 @Dependent bean，所以不是代理 AFAIK； 我什至不知道为什么要代理老实说，bean 需要一个默认构造函数 这似乎是一个实现细节或 CDI 规范中被忽略的一点。无论如何，我敢打赌它可以提出一个很好的新问题 :)

编辑:我发现了为什么可代理 bean 需要默认构造。实际上，这并不神秘:因为 bean 的代理是同一 bean 的子类，所以代理需要在其自己的构造中调用 super() 构造函数。如果它没有非私有(private)的默认构造函数，它就不知道要调用哪个构造函数。人们甚至可以想象这样一种场景，调用注入(inject)的构造函数来创建代理，但我不知道它会给 CDI 实现增加什么样的复杂性；做起来可能不是那么容易...