Apache Spark中的数据集

Dataset ds = sc.read().json("path").as(Encoders.bean(Tweet.class)); ds.show(); JavaRDD dstry = ds.toJavaRDD(); System.out.println(dstry.first().getClass()); 

 Caused by: java.util.concurrent.ExecutionException: org.codehaus.commons.compiler.CompileException: File 'generated.java', Line 50, Column 16: failed to compile: org.codehaus.commons.compiler.CompileException: File 'generated.java', Line 50, Column 16: No applicable constructor/method found for actual parameters "org.apache.spark.unsafe.types.UTF8String"; candidates are: "public void sparkSQL.Tweet.setId(long)" at org.spark_project.guava.util.concurrent.AbstractFuture$Sync.getValue(AbstractFuture.java:306) at org.spark_project.guava.util.concurrent.AbstractFuture$Sync.get(AbstractFuture.java:293) at org.spark_project.guava.util.concurrent.AbstractFuture.get(AbstractFuture.java:116) at org.spark_project.guava.util.concurrent.Uninterruptibles.getUninterruptibly(Uninterruptibles.java:135) at org.spark_project.guava.cache.LocalCache$Segment.getAndRecordStats(LocalCache.java:2410) at org.spark_project.guava.cache.LocalCache$Segment.loadSync(LocalCache.java:2380) at org.spark_project.guava.cache.LocalCache$Segment.lockedGetOrLoad(LocalCache.java:2342) at org.spark_project.guava.cache.LocalCache$Segment.get(LocalCache.java:2257) at org.spark_project.guava.cache.LocalCache.get(LocalCache.java:4000) at org.spark_project.guava.cache.LocalCache.getOrLoad(LocalCache.java:4004) at org.spark_project.guava.cache.LocalCache$LocalLoadingCache.get(LocalCache.java:4874) at org.apache.spark.sql.catalyst.expressions.codegen.CodeGenerator$.compile(CodeGenerator.scala:1369) at org.apache.spark.sql.catalyst.expressions.codegen.GenerateSafeProjection$.create(GenerateSafeProjection.scala:197) at org.apache.spark.sql.catalyst.expressions.codegen.GenerateSafeProjection$.create(GenerateSafeProjection.scala:36) at org.apache.spark.sql.catalyst.expressions.codegen.CodeGenerator.generate(CodeGenerator.scala:1325) at org.apache.spark.sql.catalyst.expressions.codegen.CodeGenerator.generate(CodeGenerator.scala:1322) at org.apache.spark.sql.execution.DeserializeToObjectExec$$anonfun$2.apply(objects.scala:90) at org.apache.spark.sql.execution.DeserializeToObjectExec$$anonfun$2.apply(objects.scala:89) at org.apache.spark.rdd.RDD$$anonfun$mapPartitionsWithIndexInternal$1$$anonfun$apply$24.apply(RDD.scala:818) at org.apache.spark.rdd.RDD$$anonfun$mapPartitionsWithIndexInternal$1$$anonfun$apply$24.apply(RDD.scala:818) at org.apache.spark.rdd.MapPartitionsRDD.compute(MapPartitionsRDD.scala:38) at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:324) at org.apache.spark.rdd.RDD.iterator(RDD.scala:288) at org.apache.spark.rdd.MapPartitionsRDD.compute(MapPartitionsRDD.scala:38) at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:324) at org.apache.spark.rdd.RDD.iterator(RDD.scala:288) at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:87) at org.apache.spark.scheduler.Task.run(Task.scala:109) at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:345) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at java.lang.Thread.run(Thread.java:748) Caused by: org.codehaus.commons.compiler.CompileException: File 'generated.java', Line 50, Column 16: failed to compile: org.codehaus.commons.compiler.CompileException: File 'generated.java', Line 50, Column 16: No applicable constructor/method found for actual parameters "org.apache.spark.unsafe.types.UTF8String"; candidates are: "public void sparkSQL.Tweet.setId(long)" at org.apache.spark.sql.catalyst.expressions.codegen.CodeGenerator$.org$apache$spark$sql$catalyst$expressions$codegen$CodeGenerator$$doCompile(CodeGenerator.scala:1435) at org.apache.spark.sql.catalyst.expressions.codegen.CodeGenerator$$anon$1.load(CodeGenerator.scala:1497) at org.apache.spark.sql.catalyst.expressions.codegen.CodeGenerator$$anon$1.load(CodeGenerator.scala:1494) at org.spark_project.guava.cache.LocalCache$LoadingValueReference.loadFuture(LocalCache.java:3599) at org.spark_project.guava.cache.LocalCache$Segment.loadSync(LocalCache.java:2379) 

当我仔细观察时，我唯一提出疑问的是：

找不到适用于实际参数的构造函数/方法“org.apache.spark.unsafe.types.UTF8String”; 候选人是：“public void sparkSQL.Tweet.setId（long）”

Answer 1

正如@ user9718686所写，id字段有不同的类型：json文件中的String ，类定义中的long 。 当您将其读入Dataset ，Spark会从文件中推断出架构并检测到该ID是String类型，这就是为什么它在您尝试打印时有效（正如您在其中一条评论中提到的那样） ）。 如果您希望将dataframe设置为Dataset ，则必须将json文件更改为使用long ID而不是String或者当您尝试对dataframe执行任何操作操作时，可以让Spark转换此id。

 Dataset rowDataset = sc.read().json("path"); Dataset tweetDataset = rowDataset .withColumn("id", rowDataset.col("id").cast(DataTypes.LongType)) .as(Encoders.bean(Tweet.class)); tweetDataset.printSchema(); System.out.println(tweetDataset.head().getId()); 

Answer 2

由于类型不匹配，它会给您一个错误：

• Tweet类将id字段定义为Long 。
• 您的数据的id为String 。

您必须转换输入或调整类定义。