Apache Spark中的數據集

Question

Dataset<Tweet> ds = sc.read().json("path").as(Encoders.bean(Tweet.class));
ds.show();
JavaRDD<Tweet> 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)

當我仔細觀察時，我唯一的疑問是：

找不到適用於實際參數“ org.apache.spark.unsafe.types.UTF8String”的適用的構造函數/方法； 候選者為：“ public void sparkSQL.Tweet.setId（long）”

Answer 1

由於類型不匹配，它給您一個錯誤：

• Tweet類將id字段定義為Long 。
• 您的數據id為String 。

您必須強制轉換輸入或調整類定義。

Answer 2

正如@ user9718686所寫，id字段具有不同的類型：json文件中的String ，類定義中的long 。 當您將其讀入Dataset<Row> ，Spark從文件中推斷出模式並檢測到id為String類型，這就是為什么當您嘗試打印它時它起作用的原因（如您在其中一條注釋中所要求的那樣） ）。 如果要將數據框設置為Dataset<Tweet> ，則必須將json文件更改為使用long id而不是String或者當您嘗試對數據框執行任何操作操作時，可以讓Spark轉換此ID。

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