Java – Mongo-Hadoop simple test failed due to NPE

This is an open question posted in the support forum But since I didn’t get any response, I thought I should try to ask questions here.

I have one that uses MongoDB as
Data layer. Currently I’m using Mongo’s Map reduce mechanism, but, me
I’m facing some performance issues. So I thought about using Hadoop
Implement the logic.

I’ve successfully run the example of the Treasury yield and came to mind
Create a simple project just to learn about the mongo-hadoop driver.
So I created a project with the appropriate jar file inserted into the build
path and run it.

Here is my java code:

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 ); " 

But I get this error :

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)

What am I doing wrong? Is this a Mongo, Hadoop, or Mongo-Hadoop problem?

You seem to have forgotten to specify the name of the collection from which you got the data.

In the example, the line looks like this:

MongoConfigUtil.setInputURI( conf, "mongodb://localhost/test.in" );

However, in your code I see:

MongoConfigUtil.setInputURI( conf, "mongodb:// 
                      username:[email protected]/locations" ); 

I’m not sure if locations is a collection name or a database name, if it’s a collection, then you can try prefixing it with the database name. If it is a database, add .yourcollectionname to the end of it.