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Sqoop, mail # user - ClassNotFoundException thrown by DBConfiguration


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ClassNotFoundException thrown by DBConfiguration
Shixiong Zhu 2013-04-19, 07:02
Hi,

I encountered a ClassNotFoundException when I used DBInputFormat. I
packaged my codes with mysql-connector-java-5.1.24.jar to abc.jar. Then I
run the following command to run:

hadoop jar abc.jar a.b.c.Main

But it is crashed by the following exception:

  Notes: java.lang.RuntimeException: java.lang.RuntimeException:
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at
org.apache.hadoop.mapreduce.lib.db.DBInputFormat.setConf(DBInputFormat.java:158)
at org.apache.hadoop.util.ReflectionUtils.setConf(ReflectionUtils.java:70)
at
org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:130)
at org.apache.hadoop.mapred.JobClient.writeNewSplits(JobClient.java:959)
at org.apache.hadoop.mapred.JobClient.writeSplits(JobClient.java:979)
at org.apache.hadoop.mapred.JobClient.access$500(JobClient.java:170)
at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:891)
at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:844)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:416)
at
org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1232)
at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:844)
at org.apache.hadoop.mapreduce.Job.submit(Job.java:481)
at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:511)
...
at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:70)
at
com.microstrategy.etl.alert.feedback.FeedbackDumpTask.main(FeedbackDumpTask.java:17)
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:616)
at org.apache.hadoop.util.RunJar.main(RunJar.java:208)
Caused by: java.lang.RuntimeException: java.lang.ClassNotFoundException:
com.mysql.jdbc.Driver
at
org.apache.hadoop.mapreduce.lib.db.DBInputFormat.getConnection(DBInputFormat.java:184)
at
org.apache.hadoop.mapreduce.lib.db.DBInputFormat.setConf(DBInputFormat.java:152)
... 25 more
Caused by: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:186)
at
org.apache.hadoop.mapreduce.lib.db.DBConfiguration.getConnection(DBConfiguration.java:143)
at
org.apache.hadoop.mapreduce.lib.db.DBInputFormat.getConnection(DBInputFormat.java:178)
... 26 more

I read the DBConfiguration.java file, and found it uses "Class.forName" to
load "com.mysql.jdbc.Driver":

   /** Returns a connection object to the DB.
   * @throws ClassNotFoundException
   * @throws SQLException */
  public Connection getConnection()
      throws ClassNotFoundException, SQLException {
    Connection connection;

    Class.forName(conf.get(DBConfiguration.DRIVER_CLASS_PROPERTY));

I think that's why my application crashed. The classloader of
DBConfiguration is sun.misc.Launcher$AppClassLoader, but
"com.mysql.jdbc.Driver" exists in the URLClassLoader created by
org.apache.hadoop.util.RunJar.
So "Class.forName" invoked by DBConfiguration can not find
"com.mysql.jdbc.Driver" in the sun.misc.Launcher$AppClassLoader.

Why does DBConfiguration not use "conf.getClassByName" to load the jdbc
driver? If DBConfiguration use the following code, it can work in such
situation.

conf.getClassByName(conf.get(DBConfiguration.DRIVER_CLASS_PROPERTY));

Is there any similar issue? Sorry that I can not find any JIRA about this
problem.

--
Thanks,
Shixiong Zhu