在hadoop中对sequenceFile进行排序时出现classcastException？

Question

我正在关注 Tom White 的 Hadoop-The definitive guide 第三版。我已成功将sequenceFile 写入HDFS。我按照作者在书中给出的示例进行操作。 但是当我尝试运行sort（第138 页）时，我得到了classCastException。堆栈跟踪在下面可用。

这里出了什么问题，需要什么修复？

hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-2.2.0.jar sort -r 1 -inFormat org.apache.hadoop.mapred.SequenceFileInputFormat -outFormat org.apache.hadoop.mapred.SequenceFileOutputFormat -outKey org.apache.hadoop.io.IntWritable -outValue org.apache.hadoop.io.Text /output/seqfile /output/sortedfile
14/07/09 10:51:53 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
14/07/09 10:51:53 INFO Configuration.deprecation: session.id is deprecated. Instead, use dfs.metrics.session-id
14/07/09 10:51:53 INFO jvm.JvmMetrics: Initializing JVM Metrics with processName=JobTracker, sessionId=
java.lang.ClassCastException: class org.apache.hadoop.mapred.SequenceFileInputFormat
    at java.lang.Class.asSubclass(Class.java:3075)
    at org.apache.hadoop.examples.Sort.run(Sort.java:104)
    at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:70)
    at org.apache.hadoop.examples.Sort.main(Sort.java:191)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.hadoop.util.ProgramDriver$ProgramDescription.invoke(ProgramDriver.java:72)
    at org.apache.hadoop.util.ProgramDriver.run(ProgramDriver.java:144)
    at org.apache.hadoop.examples.ExampleDriver.main(ExampleDriver.java:74)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:212)

Answer 1

这可能是因为您使用的是旧的 map/reduce 序列文件类。而不是使用

-inFormat org.apache.hadoop.mapred.SequenceFileInputFormat
-outFormat org.apache.hadoop.mapred.SequenceFileOutputFormat

尝试使用

-inFormat org.apache.hadoop.mapreduce.lib.input.SequenceFileInputFormat;
-outFormat org.apache.hadoop.mapreduce.lib.output.SequenceFileOutputFormat;