我在Vaadin项目中看到了这个例外。但是,功能并没有真正破坏。 run()
方法中的代码执行了打算完成的操作,但会出现此异常。
E 140619 124701.131 [Thread-2] MainUI - Uncaught throwable:
java.util.concurrent.ExecutionException: java.lang.NullPointerException
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:188)
at com.vaadin.server.VaadinSession$FutureAccess.get(VaadinSession.java:123)
at com.vaadin.server.VaadinService.runPendingAccessTasks(VaadinService.java:1802)
at com.vaadin.server.VaadinSession.unlock(VaadinSession.java:1012)
at com.vaadin.server.VaadinService.ensureAccessQueuePurged(VaadinService.java:1763)
at com.vaadin.server.VaadinService.accessSession(VaadinService.java:1729)
at com.vaadin.server.VaadinSession.access(VaadinSession.java:1402)
at com.vaadin.ui.UI.access(UI.java:1372)
发生在这里
ui.acccess(new Runnable() {
@Override
public void run() {
//code here
}
}
我该怎么办?我可以捕获异常并忽略它,或者我的代码中有错误吗?
它使用@Push注释为MainUI扩展UI,并且代码如下:
@Override
protected void init(VaadinRequest request) {
WrappedSession wrappedSession = request.getWrappedSession();
final String id = wrappedSession.getId();
log.info("Created new UI for session id {}", id);
VaadinSession.getCurrent().setErrorHandler(new DefaultErrorHandler() {
@Override
public void error(com.vaadin.server.ErrorEvent event) {
super.error(event);
log.error("Uncaught throwable: ", event.getThrowable());
}
});
...
}
[此部分由其他作者添加]
我,巴兹尔布尔克,我在同样的用法中得到了同样的例外。生产使用(不是开发)中会抛出异常。
在Mac OS X Mountain Lion上的Java 8 Update 20上使用Vaadin 7.1.3和Push with Tomcat 8.0.12。
例外:
Nov 04, 2014 4:45:50 AM com.vaadin.server.DefaultErrorHandler doDefault
SEVERE:
java.util.concurrent.ExecutionException: java.lang.NullPointerException
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at com.vaadin.server.VaadinSession$FutureAccess.get(VaadinSession.java:123)
at com.vaadin.server.VaadinService.runPendingAccessTasks(VaadinService.java:1800)
at com.vaadin.server.VaadinSession.unlock(VaadinSession.java:1013)
at com.vaadin.server.VaadinService.ensureAccessQueuePurged(VaadinService.java:1761)
at com.vaadin.server.VaadinService.accessSession(VaadinService.java:1727)
at com.vaadin.server.VaadinSession.access(VaadinSession.java:1403)
at com.vaadin.ui.UI.access(UI.java:1389)
at com.rainwatersoft.powerwrangler.curr_sup_dem.CurrSupDemReportUpdater.update(CurrSupDemReportUpdater.java:164)
at com.rainwatersoft.powerwrangler.curr_sup_dem.CurrSupDemReportUpdater.checkForUpdate(CurrSupDemReportUpdater.java:125)
at com.rainwatersoft.powerwrangler.curr_sup_dem.CurrSupDemReportUpdater.lambda$considerUpdate$2(CurrSupDemReportUpdater.java:110)
at com.rainwatersoft.powerwrangler.curr_sup_dem.CurrSupDemReportUpdater$$Lambda$3/1011224121.run(Unknown Source)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
违规代码使用Java 8的Lambda语法将Runnable传递给UI::access方法。
layout.getUI().access( () -> { // Runnable
layout.freshen( this.interval );
} );
答案 0 :(得分:0)
以下摘自我的代码:
// remember UI and request attributes
val ui = UI.getCurrent
val attributes = RequestContextHolder.getRequestAttributes
future.onSuccess {
case e => ui.access(
new Runnable {
override def run(): Unit = {
try {
RequestContextHolder.setRequestAttributes(attributes)
success.apply(e)
} finally {
RequestContextHolder.resetRequestAttributes()
}
}
}
)
}
future.onFailure {
case t => ui.access(
new Runnable {
override def run(): Unit = {
try {
_logger.error("Something goes wrong in async await request", t)
RequestContextHolder.setRequestAttributes(attributes)
failure.apply(t)
} finally {
RequestContextHolder.resetRequestAttributes()
}
}
}
)
}
我使用spring4vaadin和最新的Vaadin 7.2.x。
答案 1 :(得分:0)
我建议使用-ea参数在jvm中运行该应用程序以启用断言。通常,由于其他地方的错误代码而引发此异常。即您的ui.access(..)最有可能是正确的,但是其他一些代码实际上正在锁定UI,因此引发了异常。