"Unsatisfied dependencies" 尝试将 EJB 注入另一个组件时出现 UnsatisfiedResolutionException

Question

我正在尝试实现 Java EE 的托管执行器 ManagedExecutorService 以提交可调用任务，其中每个任务都会调用注入的 bean 方法。

我正在使用 Instance class 让容器知道任务对象，但是当执行 get() 时抛出以下异常：

Caused by: javax.ejb.EJBException: org.jboss.weld.exceptions.UnsatisfiedResolutionException: WELD-001334: Unsatisfied dependencies for type MyTask with qualifiers @Default

我在 WildFly 14 上运行。

注入的bean：

@Stateless
public class MyBean {

    public void print() {
        System.out.println("MyBean printed");
    }
}

任务：

@Stateless
public class MyTask implements Callable<String> {

    @Inject
    MyBean myBean;

    @Override
    public String call() throws Exception {

        System.out.println("MyTask called");
        myBean.print();
        return "Task called";

    }
}

任务调用者：

@Stateless
public class TestBean {

    @Inject
    Instance<MyTask> myTaskInstance;

    @Resource
    private ManagedExecutorService executor;

    public void test() throws InterruptedException, ExecutionException {

        List<Callable<String>> tasks = new ArrayList<>(); 
        MyTask task = myTaskInstance.get();  // <------- Exception is thrown here
        tasks.add(task);
        MyTask task2 = myTaskInstance.get();
        tasks.add(task2);

        List<Future<String>> taskResults = null;
        taskResults = executor.invokeAll(tasks);

        List<String> results = new ArrayList<>(); 

        for(Future<String> taskResult : taskResults) {
                results.add(taskResult.get());
        }

    }
}

为什么会抛出异常，如何解决这个问题？ class路径中是否缺少库？

Answer 1

问题是 MyTask 作为实现 Callable 的 EJB，您已经删除了 MyTask class本身来自这个bean的"bean type"，也就是说不能注入@Inject MyTask xxx "client"，按照CDI 2.0 spec里面的规则]:

18.2.2. Bean types of a session bean

The unrestricted set of bean types for a session bean contains all local interfaces of the bean and their superinterfaces. If the session bean has a no-interface view, the unrestricted set of bean types contains the bean class and all superclasses. In addition, java.lang.Object is a bean type of every session bean.

这就是为什么 Weld 找不到有效的 MyTask bean 来满足对 TestBean 客户端的注入。

您可以通过添加 @LocalBean 注释为 MyTask EJB 提供无接口视图，例如：

@Stateless
@LocalBean
public class MyTask implements Callable<String> {

或者，您可以删除 implements Callable 并重构为：

public class MyTask {

    @Inject
    MyBean myBean;

    MyCallable callable = new MyCallable();

    public Callable getCallable() {
        return callable;
    }

    private class MyCallable implements Callable<String> {
        @Override
        public String call() throws Exception {

            System.out.println("MyTask called");
            myBean.print();
            return "Task called";
        }
    }
}    

public class TestBean {

    // ...

    MyTask task = myTaskInstance.get(); 
    tasks.add(task.getCallable())

    // ...
}

有关更多讨论，请参阅 here for a quick reference on the no-interface view, as well as this post。

"Unsatisfied dependencies" 尝试将 EJB 注入另一个组件时出现 UnsatisfiedResolutionException

"Unsatisfied dependencies" with UnsatisfiedResolutionException when trying to inject EJB into another component

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ejb

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