【发布时间】：2018-04-12 09:08:03
【问题描述】：
我正在尝试在 Play Framework 中创建一个简单的论坛系统，但我遇到了一个奇怪的错误。我有一个 forum.java 类，它是错误的来源，但不管里面的代码如何，它总是在第 6 行抛出一个空指针。我认为这里有尽可能多的相关内容。
package models;
import io.ebean.Finder;
import io.ebean.Model;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import java.util.List;
@Entity
public class Forum extends Model {
@Id
private String id;
@ManyToOne(cascade = CascadeType.ALL)
private List<Thread> threads;
有问题的行是 javax.persistence.CascadeType 导入，但我已经删除了它，将其向下移动，重新创建了类。无论如何，错误继续在第 6 行抛出。它也没有解释导致空指针的原因。当行为空时它甚至会抛出。
作为参考，我还有很多其他类以相同的格式布局。我尝试在 sbt 控制台中清理项目，并尝试从头开始重新制作课程。我确定这是某种基本错误，但我什至不知道从哪里开始。
编辑：添加了 Stacktrace
[info] play.api.Play - Application started (Dev)
[error] application -
! @77hm04h99 - Internal server error, for (GET) [/forum/1] ->
play.api.http.HttpErrorHandlerExceptions$$anon$1: Execution exception[[NullPointerException: null]]
at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:255)
at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler.scala:182)
at play.core.server.AkkaHttpServer$$anonfun$2.applyOrElse(AkkaHttpServer.scala:320)
at play.core.server.AkkaHttpServer$$anonfun$2.applyOrElse(AkkaHttpServer.scala:318)
at scala.concurrent.Future.$anonfun$recoverWith$1(Future.scala:414)
at scala.concurrent.impl.Promise.$anonfun$transformWith$1(Promise.scala:37)
at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60)
at akka.dispatch.BatchingExecutor$AbstractBatch.processBatch(BatchingExecutor.scala:55)
at akka.dispatch.BatchingExecutor$BlockableBatch.$anonfun$run$1(BatchingExecutor.scala:91)
at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
Caused by: java.lang.NullPointerException: null
at io.ebeaninternal.server.deploy.BeanPropertyAssocMany.createReference(BeanPropertyAssocMany.java:652)
at io.ebeaninternal.server.deploy.BeanDescriptor.lazyLoadMany(BeanDescriptor.java:2082)
at io.ebeaninternal.server.deploy.BeanDescriptor.lazyLoadMany(BeanDescriptor.java:2071)
at io.ebeaninternal.server.loadcontext.DLoadBeanContext$LoadBuffer.loadBean(DLoadBeanContext.java:172)
at io.ebean.bean.EntityBeanIntercept.loadBeanInternal(EntityBeanIntercept.java:812)
at io.ebean.bean.EntityBeanIntercept.loadBean(EntityBeanIntercept.java:785)
at io.ebean.bean.EntityBeanIntercept.preGetter(EntityBeanIntercept.java:885)
at models.Forum._ebean_get_threads(Forum.java:6)
at models.Forum.getThreads(Forum.java:37)
at views.html.forum$.apply(forum.template.scala:41)
堆栈跟踪 v2：
[error] application -
! @77hpce3hh - Internal server error, for (GET) [/forum/1] ->
play.api.http.HttpErrorHandlerExceptions$$anon$1: Execution exception[[PersistenceException: Query threw SQLException:Column "T1.FORUM_ID" not found; SQL statement:
select t0.id, t1.id, t1.title, t1.replies, t1.last_reply, t1.forum_id from forum t0 left join thread t1 on t1.forum_id = t0.id where t0.id = ? order by t0.id [42122-196] Bind values:[null] Query was:select t0.id, t1.id, t1.title, t1.replies, t1.last_reply, t1.forum_id from forum t0 left join thread t1 on t1.forum_id = t0.id where t0.id = ? order by t0.id]]
at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:255)
at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler.scala:182)
at play.core.server.AkkaHttpServer$$anonfun$2.applyOrElse(AkkaHttpServer.scala:320)
at play.core.server.AkkaHttpServer$$anonfun$2.applyOrElse(AkkaHttpServer.scala:318)
at scala.concurrent.Future.$anonfun$recoverWith$1(Future.scala:414)
at scala.concurrent.impl.Promise.$anonfun$transformWith$1(Promise.scala:37)
at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60)
at akka.dispatch.BatchingExecutor$AbstractBatch.processBatch(BatchingExecutor.scala:55)
at akka.dispatch.BatchingExecutor$BlockableBatch.$anonfun$run$1(BatchingExecutor.scala:91)
at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
Caused by: javax.persistence.PersistenceException: Query threw SQLException:Column "T1.FORUM_ID" not found; SQL statement:
select t0.id, t1.id, t1.title, t1.replies, t1.last_reply, t1.forum_id from forum t0 left join thread t1 on t1.forum_id = t0.id where t0.id = ? order by t0.id [42122-196] Bind values:[null] Query was:select t0.id, t1.id, t1.title, t1.replies, t1.last_reply, t1.forum_id from forum t0 left join thread t1 on t1.forum_id = t0.id where t0.id = ? order by t0.id
at io.ebean.config.dbplatform.SqlCodeTranslator.translate(SqlCodeTranslator.java:48)
at io.ebean.config.dbplatform.DatabasePlatform.translate(DatabasePlatform.java:195)
at io.ebeaninternal.server.query.CQueryEngine.translate(CQueryEngine.java:139)
at io.ebeaninternal.server.query.DefaultOrmQueryEngine.translate(DefaultOrmQueryEngine.java:38)
at io.ebeaninternal.server.core.OrmQueryRequest.translate(OrmQueryRequest.java:81)
at io.ebeaninternal.server.query.CQuery.createPersistenceException(CQuery.java:666)
at io.ebeaninternal.server.query.CQueryEngine.find(CQueryEngine.java:422)
at io.ebeaninternal.server.query.DefaultOrmQueryEngine.findId(DefaultOrmQueryEngine.java:162)
at io.ebeaninternal.server.core.OrmQueryRequest.findId(OrmQueryRequest.java:327)
at io.ebeaninternal.server.core.DefaultServer.findId(DefaultServer.java:1175)
Caused by: org.h2.jdbc.JdbcSQLException: Column "T1.FORUM_ID" not found; SQL statement:
select t0.id, t1.id, t1.title, t1.replies, t1.last_reply, t1.forum_id from forum t0 left join thread t1 on t1.forum_id = t0.id where t0.id = ? order by t0.id [42122-196]
at org.h2.message.DbException.getJdbcSQLException(DbException.java:345)
at org.h2.message.DbException.get(DbException.java:179)
at org.h2.message.DbException.get(DbException.java:155)
at org.h2.expression.ExpressionColumn.optimize(ExpressionColumn.java:147)
at org.h2.command.dml.Select.prepare(Select.java:839)
at org.h2.command.Parser.prepareCommand(Parser.java:263)
at org.h2.engine.Session.prepareLocal(Session.java:578)
at org.h2.engine.Session.prepareCommand(Session.java:519)
at org.h2.jdbc.JdbcConnection.prepareCommand(JdbcConnection.java:1204)
at org.h2.jdbc.JdbcPreparedStatement.<init>(JdbcPreparedStatement.java:73)
【问题讨论】：
-
运行
clean命令，你的类可能不是最新的。 -
我试过了，很遗憾。通常这是我解决此类奇怪问题的首选方法，但它似乎不起作用。我会通过请我组中的其他人尝试运行它，看看它是否是我的环境的问题
-
您可以在问题中包含完整的 stackTrace 吗？
-
对。将其添加到问题中。就上下文而言，发生这种情况的时间是我加载论坛页面的时候。我有一系列子论坛，每当我点击进入一个，它应该确定要在论坛视图上加载哪个论坛，然后获取已发布在那里的主题列表。
-
at io.ebeaninternal.server.deploy.BeanPropertyAssocMany让我认为您定义了ManyToOne、OneToMany或ManyToMany错误。你可能想检查一下。
标签： java playframework nullpointerexception persistence ebean