不能将 CompositeInputFormat 与 Hadoop 一起使用，抛出异常表达式为空

Question

我正在使用CDH4（4.5）中的MRV1，并且面临CompositeInputFormat的问题。我尝试加入多少输入都没关系。为了简单起见，这是一个只有一个输入的示例：

    Configuration conf = new Configuration();
    Job job = new Job(conf, "Blah");
    job.setJarByClass(Blah.class);
    job.setMapperClass(Blah.BlahMapper.class);
    job.setReducerClass(Blah.BlahReducer.class);
    job.setMapOutputKeyClass(LongWritable.class);
    job.setMapOutputValueClass(BlahElement.class);
    job.setOutputKeyClass(LongWritable.class);
    job.setOutputValueClass(BlahElement.class);
    job.setInputFormatClass(CompositeInputFormat.class);
    String joinStatement = CompositeInputFormat.compose("inner", SequenceFileInputFormat.class, "/someinput");
    System.out.println(joinStatement);
    conf.set("mapred.join.expr", joinStatement);
    job.setOutputFormatClass(SequenceFileOutputFormat.class);
    FileOutputFormat.setOutputPath(job, new Path(newoutput));
    return job.waitForCompletion(true) ? 0 : 1;

这是输出 stacktrace：

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/hadoop2/share/hadoop/mapreduce1/lib/slf4j-log4j12-1.6.1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/hadoop2/share/hadoop/common/lib/slf4j-log4j12-1.6.1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
14/01/31 03:27:47 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
inner(tbl(org.apache.hadoop.mapreduce.lib.input.SequenceFileInputFormat,"/someinput"))
14/01/31 03:27:48 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same.
14/01/31 03:27:51 INFO mapred.JobClient: Cleaning up the staging area hdfs://archangel-desktop:54310/tmp/hadoop/mapred/staging/hadoop/.staging/job_201401302213_0013
14/01/31 03:27:51 ERROR security.UserGroupInformation: PriviledgedActionException as:hadoop (auth:SIMPLE) cause:java.io.IOException: Expression is null
Exception in thread "main" java.io.IOException: Expression is null
    at org.apache.hadoop.mapreduce.lib.join.Parser.parse(Parser.java:542)
    at org.apache.hadoop.mapreduce.lib.join.CompositeInputFormat.setFormat(CompositeInputFormat.java:85)
    at org.apache.hadoop.mapreduce.lib.join.CompositeInputFormat.getSplits(CompositeInputFormat.java:127)
    at org.apache.hadoop.mapred.JobClient.writeNewSplits(JobClient.java:1079)
    at org.apache.hadoop.mapred.JobClient.writeSplits(JobClient.java:1096)
    at org.apache.hadoop.mapred.JobClient.access$600(JobClient.java:177)
    at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:995)
    at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:948)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:415)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1408)
    at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:948)
    at org.apache.hadoop.mapreduce.Job.submit(Job.java:566)
    at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:596)
    at com.nileshc.graphfu.pagerank.BlockMatVec.run(BlockMatVec.java:79)
    at com.nileshc.graphfu.Main.main(Main.java:21)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:208)

有人曾经面对过这个吗？关于如何解决的想法？

Answer 1

我的糟糕。

conf.set("mapred.join.expr", joinStatement);

以上应该是：

job.getConfiguration().set("mapreduce.join.expr", joinStatement);

和：

String joinStatement = CompositeInputFormat.compose("inner", SequenceFileInputFormat.class, "/someinput");

^^应该是：

String joinStatement = CompositeInputFormat.compose("inner", SequenceFileInputFormat.class, new Path("/someinput"));

第一个更改是使所有不同的变化。

Answer 2

在上述代码中，

conf.set("mapred.join.expr", joinStatement);

在创建作业遵守后，上述行进行了编码。因此，很明显，工作对象不知道此配置！！！！

请参阅下面的修订代码： -

Configuration conf = new Configuration();
conf.set("mapred.join.expr", joinStatement);
Job job = new Job(conf, "Blah");
job.setJarByClass(Blah.class);
.
.
.
.
.

以下是相反： -

job.getConfiguration().set("mapreduce.join.expr", joinStatement);

使用上述代码而不是

conf.set("mapred.join.expr", joinStatement);