我無法理解此代碼無法工作的原因。基本上我想要一個parallelStream()函數期間訪問從CDI ViewScoped豆一CDI SessionScoped豆,我得到這個異常:訪問CDI SessionScoped bean在Java 8並行流中不起作用
WELD-001303: No active contexts for scope type javax.enterprise.context.SessionScoped
這在Wildfly 10.1運行。
的ViewScoped豆:
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"));
}
}
的SessionScoped豆:
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";
}
}
的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>
堆棧跟蹤:
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)
我們的理論,本次會議可能是特定於線程的,但沒有硬證據。
也很好奇,如果有解決方法。真正的代碼比這複雜得多,所以我們不能事先預加載SessionController結果而不會失去並行流的好處。
我還沒有看到過一個真實世界的情況,其中parellel流是出於性能原因至關重要 –
在這種情況下,我在每個函數中引發不同的SQL查詢,所以我只需要等待最長的一個完成對我們的SQL Server。 –
並行流並不意味着在IO操作中使用。相反,它們旨在用於執行並行計算,例如通過將列表劃分爲N個部分並且並行執行N個部分列表的總和並最終總結子結果來對總長列表的元素進行求和,並最終對子結果進行求和 –