Question

我在尝试搜索列表中的特定Java对象时遇到了问题。
实际上我得到了我想为另一个Java类工作的搜索功能。现在我尝试了另一个但不是返回结果列表我得到一个NullPointerException。

这就是我的功能：

 public static List<Customer> searchByEverything(String keyword){
    List<Customer> customerList = find.all(); //Using java Ebean

    System.out.println(keyword); //Check if keyword is not empty
    System.out.println(customerList); //Check if list is not empty

    Predicate<Customer> customerPredicate = u -> u.name.toLowerCase().contains(keyword.toLowerCase());

    try{
        return customerList.stream().filter(customerPredicate).collect(Collectors.toList());
    }catch (Exception e){
        e.printStackTrace();
    }

这是Exception e：

的痕迹

java.lang.NullPointerException
at models.Customer.lambda$searchByEverything$2(Customer.java:174)
at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:174)
at java.util.ArrayList$Itr.forEachRemaining(ArrayList.java:891)
at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
at models.Customer.searchByEverything(Customer.java:179)
at controllers.Application.searchCustomers(Application.java:262)
at router.Routes$$anonfun$routes$1$$anonfun$applyOrElse$17$$anonfun$apply$17.apply(Routes.scala:479)
at router.Routes$$anonfun$routes$1$$anonfun$applyOrElse$17$$anonfun$apply$17.apply(Routes.scala:479)
at play.core.routing.HandlerInvokerFactory$$anon$4.resultCall(HandlerInvoker.scala:157)
at play.core.routing.HandlerInvokerFactory$$anon$4.resultCall(HandlerInvoker.scala:156)
at play.core.routing.HandlerInvokerFactory$JavaActionInvokerFactory$$anon$14$$anon$3$$anon$1.invocation(HandlerInvoker.scala:136)
at play.core.j.JavaAction$$anon$1.call(JavaAction.scala:73)
at play.http.HttpRequestHandler$1.call(HttpRequestHandler.java:54)
at play.mvc.Security$AuthenticatedAction.call(Security.java:53)
at play.core.j.JavaAction$$anonfun$7.apply(JavaAction.scala:108)
at play.core.j.JavaAction$$anonfun$7.apply(JavaAction.scala:108)
at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24)
at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)
at play.core.j.HttpExecutionContext$$anon$2.run(HttpExecutionContext.scala:56)
at play.api.libs.iteratee.Execution$trampoline$.execute(Execution.scala:70)
at play.core.j.HttpExecutionContext.execute(HttpExecutionContext.scala:48)
at scala.concurrent.impl.Future$.apply(Future.scala:31)
at scala.concurrent.Future$.apply(Future.scala:492)
at play.core.j.JavaAction.apply(JavaAction.scala:108)
at play.api.mvc.Action$$anonfun$apply$2$$anonfun$apply$5$$anonfun$apply$6.apply(Action.scala:112)
at play.api.mvc.Action$$anonfun$apply$2$$anonfun$apply$5$$anonfun$apply$6.apply(Action.scala:112)
at play.utils.Threads$.withContextClassLoader(Threads.scala:21)
at play.api.mvc.Action$$anonfun$apply$2$$anonfun$apply$5.apply(Action.scala:111)
at play.api.mvc.Action$$anonfun$apply$2$$anonfun$apply$5.apply(Action.scala:110)
at scala.Option.map(Option.scala:146)
at play.api.mvc.Action$$anonfun$apply$2.apply(Action.scala:110)
at play.api.mvc.Action$$anonfun$apply$2.apply(Action.scala:103)
at scala.concurrent.Future$$anonfun$flatMap$1.apply(Future.scala:251)
at scala.concurrent.Future$$anonfun$flatMap$1.apply(Future.scala:249)
at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:32)
at akka.dispatch.BatchingExecutor$AbstractBatch.processBatch(BatchingExecutor.scala:55)
at akka.dispatch.BatchingExecutor$BlockableBatch$$anonfun$run$1.apply$mcV$sp(BatchingExecutor.scala:91)
at akka.dispatch.BatchingExecutor$BlockableBatch$$anonfun$run$1.apply(BatchingExecutor.scala:91)
at akka.dispatch.BatchingExecutor$BlockableBatch$$anonfun$run$1.apply(BatchingExecutor.scala:91)
at scala.concurrent.BlockContext$.withBlockContext(BlockContext.scala:72)
at akka.dispatch.BatchingExecutor$BlockableBatch.run(BatchingExecutor.scala:90)
at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:39)
at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:415)
at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

正如我所说，我为不同的类实现了完全相同的搜索，并且它的工作完全正常。 customerList和keyword都不为空。在我的customerList和另一个列表中搜索之间的唯一区别是它有大约4500个对象，每个对象有大约50个属性。也许这就是问题所在？

提前谢谢！

Answer 1

很可能u.name是null

尝试更改<{p>}中的Predicate

Predicate<Customer> customerPredicate = u -> (u.name != null && u.name.toLowerCase().contains(keyword.toLowerCase()));

要查看具有name == null的Customer实例，您可以在链中添加peek方法。

customerList.stream()
.peek(c -> { 
   if (c.name == null) {
      // do something...
   }
}).filter(customerPredicate).collect(Collectors.toList());

在Java列表上尝试stream（）。filter（）。collect（Collectors.toList（））时获取NullPointerException

1 个答案: