Question

void fireQuery()
{
    String rows = "";
    engine = new ExecutionEngine( graphDB );
    Transaction tx = graphDB.beginTx();

    try
    {
        ExecutionResult result = engine.execute("START n = node(*) RETURN n");


        for ( Map<String, Object> row : result )  //THIS IS THE LINE WHERE ERROR IS OCCURING
        {
            for ( Entry<String, Object> column : row.entrySet() )
            {
                rows += column.getKey() + ": " + column.getValue() + "; ";
            }
            rows += "\n";
        }

        tx.success();
    }
    finally
    {
        tx.finish();
    }
}

我收到以下错误消息

Exception in thread "main" java.lang.NullPointerException
at org.neo4j.kernel.impl.nioneo.xa.NioNeoDbPersistenceSource.getHighestPossibleIdInUse(NioNeoDbPersistenceSource.java:111)
at org.neo4j.kernel.impl.core.NodeManager.getHighestPossibleIdInUse(NodeManager.java:983)
at org.neo4j.kernel.impl.core.NodeManager$1.<init>(NodeManager.java:354)
at org.neo4j.kernel.impl.core.NodeManager.getAllNodes(NodeManager.java:352)
at org.neo4j.tooling.GlobalGraphOperations$1.iterator(GlobalGraphOperations.java:66)
at org.neo4j.cypher.internal.spi.gdsimpl.GDSBackedQueryContext$$anon$1.all(GDSBackedQueryContext.scala:90)
at org.neo4j.cypher.internal.executionplan.builders.GraphGlobalStartBuilder$$anonfun$createStartPipe$1.apply(GraphGlobalStartBuilder.scala:50)
at org.neo4j.cypher.internal.executionplan.builders.GraphGlobalStartBuilder$$anonfun$createStartPipe$1.apply(GraphGlobalStartBuilder.scala:50)
at org.neo4j.cypher.internal.pipes.StartPipe$$anonfun$internalCreateResults$1.apply(StartPipe.scala:36)
at org.neo4j.cypher.internal.pipes.StartPipe$$anonfun$internalCreateResults$1.apply(StartPipe.scala:35)
at scala.collection.Iterator$$anon$13.hasNext(Iterator.scala:371)
at org.neo4j.cypher.internal.ClosingIterator$$anonfun$hasNext$1.apply$mcZ$sp(ClosingIterator.scala:36)
at org.neo4j.cypher.internal.ClosingIterator$$anonfun$hasNext$1.apply(ClosingIterator.scala:35)
at org.neo4j.cypher.internal.ClosingIterator$$anonfun$hasNext$1.apply(ClosingIterator.scala:35)
at org.neo4j.cypher.internal.ClosingIterator.failIfThrows(ClosingIterator.scala:86)
at org.neo4j.cypher.internal.ClosingIterator.hasNext(ClosingIterator.scala:35)
at org.neo4j.cypher.PipeExecutionResult.hasNext(PipeExecutionResult.scala:157)
at scala.collection.Iterator$$anon$11.hasNext(Iterator.scala:327)
at scala.collection.convert.Wrappers$IteratorWrapper.hasNext(Wrappers.scala:29)
at org.neo4j.cypher.PipeExecutionResult$$anon$1.hasNext(PipeExecutionResult.scala:73)
at Test.MAIN.fireQuery(MAIN.java:75)
at Test.MAIN.main(MAIN.java:60)

engine在类的函数外声明，类型为ExecutionEngine。 graphDB在类外声明，类型为GraphDatabaseService，并在调用函数fireQuery之前引用对象

Answer 1

这有点像类路径问题或其他线程可能尝试关闭graphdb，而迭代结果仍在进行中。请发布包含最新完整启动输出的graph.db/messages.log尾部以进行进一步分析（可能不是内联，可能是在pastebin或其他工具上）。

请您使用groovy运行https://gist.github.com/sarmbruster/6658637并查看错误是否仍然存在？当然，请更改graphdb实例的路径。

迭代Cypher查询时出现空指针异常

1 个答案: