I've been trying to figure out how execute my Map/Reduce job for almost 2 days now. I keep getting a ClassNotFound exception.
I've installed a Hadoop cluster in Ubuntu using Cloudera CDH4.3.0. The .java file (DemoJob.java which is not inside any package) is inside a folder called inputs and all required jar files are inside inputs/lib.
I followed http://www.cloudera.com/content/cloudera-content/cloudera-docs/HadoopTutorial/CDH4/Hadoop-Tutorial/ht_topic_5_2.html for reference.
I compile the .java file using:
javac -cp "inputs/lib/hadoop-common.jar:inputs/lib/hadoop-map-reduce-core.jar" -d Demo inputs/DemoJob.java
(In the link, it says -cp should be "/usr/lib/hadoop/:/usr/lib/hadoop/client-0.20/". But I don't have those folders in my system at all)
Create jar file using:
jar cvf Demo.jar Demo
Move 2 input files to HDFS
(Now this is where I'm confused. Do I need to move the jar file to HDFS as well? It doesn't say so in the link. But if it is not in HDFS, then how does the hadoop jar .. command work? I mean how does it combine the jar file which is in Linux system and the input files which are in HDFS?)
I run my code using:
hadoop jar Demo.jar DemoJob /Inputs/Text1.txt /Inputs/Text2.txt /Outputs
I keep getting ClassNotFoundException : DemoJob.
Somebody please help.
The class not found exception only means that some class wasn't found when class DemoJob was loaded. The missing class could have been a class referenced (imported, for example) by DemoJob. I think the problem is that you don't have the /usr/lib/hadoop/:/usr/lib/hadoop/client-0.20/ folders (classes) in your class path. It's the classes that should be there but aren't that probably are triggering the class not found exception.
Finally figured out what the problem was. Instead of creating a jar file from a folder, I directly created the jar file from the .class files using jar -cvf Demo.jar *.class
This resolved the ClassNotFound error. But I don't understand why it was not working earlier. Even when I created the jar file from a folder, I did mention the folder name when executing the class file as:hadoop jar Demo.jar Demo.DemoJob /Inputs/Text1.txt /Inputs/Text2.txt /Outputs
Related
I am running an MR job using yarn jar command and it creates a temporary jar in /tmp folder which fills up the entire disk space. I want to redirect the path of this jar to some other folder where I have more disk space. On this link, I came to know that we can change the path by setting the property mapred.local.dir for hadoop version 1.x. I am using the following command to run the jar
yarn jar myjar.jar MyClass myyml.yml arg1 -D mapred.local.dir="/grid/1/uie/facts"
The above argument mapred.local.dir doesn't change the path and it is still creating the jar in tmp folder.
Found the hack to not write the unjar file to /tmp folder. Apparently, it is not a configurable behaviour, so we can avoid the use of 'hadoop jar' or 'yarn jar'(RunJar utility) by invoking instead with the generated classpath:
java -cp $(hadoop classpath):my-fat-jar-with-all-dependencies.jar
your.app.mainClass
1. Reference link
To produce jar from hadoop mapreduce program(mapreduce wordcount example) i used maven.
Here i successfully done 'clean' and 'install'.
Also 'build' successfully by running as a Java Application by including arguments(input and output).
And it provided expected result successfully.
Now the problem is not running on hadoop.
Giving the following error:
Exception in thread "main" java.lang.ClassNotFoundException: WordCount
Is maven JAR runnable on hadoop?
Maven is a build tool which creates a Java Artifact. Any JAR containing the hadoop dependencies and the class having main() method in the Manifest file should be working with the hadoop.
Try running your JAR using the below command
hadoop jar your-jar.jar wordcount input output
where "wordcount" is the name of the class with main method,"input" and "output" are the arguments.
Two things
1) I think you are missing the package details before the classname. Copy your package name and put it before the classname and it should work.
hadoop jar /home/user/examples.jar com.test.examples.WordCount /home/user/inputfolder /home/user/outputfolder
PS: If you are using a jar for which the source code is not available with you, you can do
jar -tvf /home/user/examples.jar
and it will print all the classses with their folder names. Replace the "/" with "." (dot) and you get the package name. But this needs JDK (not JRE) in the PATH.
2) You are trying to run a MapReduce program from a Windows prompt. Are you sure you have Hadoop installed on your Windows?
hey hi I have written code and i tried running the jar but i got an exception saying that jar file cannot be opened and i even changed the file permissions and path is also set right but it is still showing me error saying that jar file cannot be opened.
Please suggest some solutions.
that is the error i got and even i have gone through the wordcount example also but could not get any answer.
Is your jar file in local file system or hdfs? The jar file should be in local file system.
I have a hadoop job which gets its input from azure documentdb. I have put the documentdb jar dependency files under a directory called 'lib'. However when I ran the job it gives me a ClassNotFound error message for one of the classes in the jar file. I also tried adding the jar files using the -libjars option but it didn't work either. Does anyone have any idea what can be wrong?
I am learning Hadoop with book 'Hadoop in Action' by Chuck Lam. In first chapter the books says that Hadoop installation will have example jar and by running 'hadoop jar hadoop-*-examples.jar' will show all the examples. But when I run the command then it throw error 'Could not find or load main class org.apache.hadoop.util.RunJar'. My guess is that installed Hadoop doesn't have example jar. I have installed 'hadoop-2.1.0-beta.tar.gz' on cygwin on Win 7 laptop. Please suggest how to get example jar.
run following command
hadoop jar PathToYourJarFile wordcount inputPath OutputPath
you can get examples jar file at your hadoop installation directory
What I can suggest here is you should manually go to the Hadoop installation directory and look for a jar name similar to hadoop-examples.jar yourself. Different distribution can have different names for the jar.
If you are in Cygwin, while in the Hadoop Installation directory you can also do a ls *examples*.jar to find the same, narrowing down the file listing to any jar file containing examples as a string.
You can then directly use the jar file name like --
hadoop jar <exampleJarYourFound.jar>
Hope this takes you to a solution.