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這是一個未解決的問題，發佈在支持論壇here上，但由於我沒有得到任何答覆，我以爲我應該試着在這裏問。Mongo-Hadoop簡單測試與NPE失敗
我有一個現有的應用程序使用MongoDB作爲 數據層。目前我正在使用Mongo的Map減少機制，但是，我正面臨着一些性能問題。所以我想到了使用Hadoop來實現這個邏輯的 。
我已經成功運行了國庫產量示例，並且想到 創建了一個簡單的項目，以便了解mongo-hadoop驅動程序。 所以我創建了一個項目，在構建 路徑中插入相應的jar文件並運行它。
這是我的Java代碼：
final Configuration conf = new Configuration();
MongoConfigUtil.setInputURI(conf, "mongodb://
username:[email protected]/locations");
MongoConfigUtil.setOutputURI(conf, "mongodb://localhost/
test.out");
System.out.println("Conf: " + conf);
final Job job = new Job(conf, "word count");
job.setJarByClass(WordCount.class);
job.setMapperClass(TokenizerMapper.class);
job.setCombinerClass(IntSumReducer.class);
job.setReducerClass(IntSumReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
job.setInputFormatClass(MongoInputFormat.class);
job.setOutputFormatClass(MongoOutputFormat.class);
System.exit(job.waitForCompletion(true) ? 0 : 1);"
，但我收到此錯誤：
Conf: Configuration: core-default.xml, core-site.xml
12/05/20 14:12:03 WARN util.NativeCodeLoader: Unable to load native-
hadoop library for your platform... using builtin-java classes where
applicable
12/05/20 14:12:03 WARN mapred.JobClient: Use GenericOptionsParser for
parsing the arguments. Applications should implement Tool for the
same.
12/05/20 14:12:03 WARN mapred.JobClient: No job jar file set. User
classes may not be found. See JobConf(Class) or
JobConf#setJar(String).
12/05/20 14:12:03 INFO mapred.JobClient: Cleaning up the staging area
file:/tmp/hadoop-maximos/mapred/staging/maximos1261801897/.staging/
job_local_0001
Exception in thread "main" java.lang.NullPointerException
at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:
796)
at com.mongodb.DBApiLayer.doGetCollection(DBApiLayer.java:116)
at com.mongodb.DBApiLayer.doGetCollection(DBApiLayer.java:43)
at com.mongodb.DB.getCollection(DB.java:81)
at
com.mongodb.hadoop.util.MongoSplitter.calculateSplits(MongoSplitter.java:
51)
at
com.mongodb.hadoop.MongoInputFormat.getSplits(MongoInputFormat.java:
51)
at org.apache.hadoop.mapred.JobClient.writeNewSplits(JobClient.java:
962)
at org.apache.hadoop.mapred.JobClient.writeSplits(JobClient.java:979)
at org.apache.hadoop.mapred.JobClient.access$600(JobClient.java:174)
at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:897)
at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:850)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:416)
at
org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.j ava:
1093)
at
org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:
850)
at org.apache.hadoop.mapreduce.Job.submit(Job.java:500)
at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:530)
at
com.mongodb.hadoop.examples.wordcount.WordCount.main(WordCount.java:
100)
我做錯了嗎？這是Mongo，Hadoop還是Mongo-Hadoop問題？