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访问CDI SessionScoped bean在Java 8并行流中不起作用

2019-10-26 04:01:42 作者：互联网

我无法理解为什么此代码不起作用.基本上,我想在parallelStream()函数期间从CDI ViewScoped Bean访问CDI SessionScoped Bean,但出现了以下异常：

WELD-001303: No active contexts for scope type javax.enterprise.context.SessionScoped

它在Wildfly 10.1中运行.

ViewScoped bean：

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
import javax.faces.view.ViewScoped;
import javax.inject.Inject;
import javax.inject.Named;

@ViewScoped
@Named
public class TestController implements Serializable {
    private static final long serialVersionUID = 1L;

    @Inject SessionController sessionController;

    public void works() {
        List<Function<String, String>> functions = new ArrayList<>();
        functions.add((String input) -> {
            return sessionController.getSomething();
        });
        functions.add((String input) -> {
            return sessionController.getSomethingElse();
        });
        functions.stream().forEach(f -> f.apply("input"));
    }

    public void doesNotWork() {
        List<Function<String, String>> functions = new ArrayList<>();
        functions.add((String input) -> {
            return sessionController.getSomething();
        });
        functions.add((String input) -> {
            return sessionController.getSomethingElse();
        });
        functions.parallelStream().forEach(f -> f.apply("input"));
    }
}

SessionScoped bean：

import java.io.Serializable;
import javax.enterprise.context.SessionScoped;
import javax.inject.Named;

@Named
@SessionScoped
public class SessionController implements Serializable {
    private static final long serialVersionUID = 1L;

    public String getSomething() {
        return "something";
    }
    public String getSomethingElse() {
        return "else";
    }
}

XHTML：

<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:p="http://primefaces.org/ui">

    <h:head />

    <h:body>
        <h:form>
            <p:commandButton value="Works" action="#{testController.works}" />
            <br />
            <p:commandButton value="Does Not Work" action="#{testController.doesNotWork}" />
        </h:form>
    </h:body>
</html>

堆栈跟踪：

Caused by: org.jboss.weld.context.ContextNotActiveException: WELD-001303: No active contexts for scope type javax.enterprise.context.SessionScoped
    at org.jboss.weld.manager.BeanManagerImpl.getContext(BeanManagerImpl.java:689)
    at org.jboss.weld.bean.ContextualInstanceStrategy$DefaultContextualInstanceStrategy.getIfExists(ContextualInstanceStrategy.java:90)
    at org.jboss.weld.bean.ContextualInstanceStrategy$CachingContextualInstanceStrategy.getIfExists(ContextualInstanceStrategy.java:165)
    at org.jboss.weld.bean.ContextualInstance.getIfExists(ContextualInstance.java:63)
    at org.jboss.weld.bean.proxy.ContextBeanInstance.getInstance(ContextBeanInstance.java:83)
    at org.jboss.weld.bean.proxy.ProxyMethodHandler.getInstance(ProxyMethodHandler.java:125)
    at com.SessionController$Proxy$_$$_WeldClientProxy.getSomething(Unknown Source)
    at com.TestController.lambda$3(TestController.java:33)
    at com.TestController.lambda$5(TestController.java:38)
    at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
    at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
    at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
    at java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:291)
    at java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:731)
    at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
    at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
    at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
    at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)

我们有理论认为会话可能是特定于线程的,但没有确凿的证据.

也想知道是否有解决方法.实际的代码要比这复杂得多,因此我们无法在不失去并行流优势的情况下预先预加载SessionController结果.

解决方法:

我认为您碰到的是使用并行流意味着您将在多个线程中运行.现在,CDI和上下文存在问题,因为您需要上下文传播-例如在主线程中,您当前具有(例如)会话上下文处于活动状态,但是在创建另一个线程时,该线程在该线程中未处于活动状态.

Chapter 6.3 in spec对其进行了更深入的描述,但为了给您一个简短的故事-默认情况下,无法将上下文传播到其他线程.这样做有充分的理由-这将非常昂贵(同步),并且您将需要解决非常奇怪的情况的负载,例如拥有一个线程无效会话,从而在其他线程对其进行操作时停用会话上下文.还有更多这样的情况.

此外,也没有内置的解决方法.但是,您可以做的是实现自己的范围或增强现有的会话范围,但是我想那将非常复杂.

标签：java-8,jsf,cdi,jsf-2,java
来源： https://codeday.me/bug/20191026/1933823.html