我正在编写我的第一个 Hadoop 应用程序，但出现错误。我不太明白这个堆栈跟踪中的一些细节是什么意思。这是一个ClassNotFoundException。我在 Ubuntu Linux v12.10、Eclipse 3.8.0、Java 1.6.0_24 上构建它。我通过从 Apache 站点下载 Hadoop 并使用 Ant 构建它来安装 Hadoop。
当我创建工作时，我的崩溃发生在程序的第一行。
public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException {
Job job = new Job(); <<== crashing here.
Program [Java Application]
com.sandbox.hadoop.Program at localhost:33878
Thread [main] (Suspended (exception ClassNotFoundException))
owns: Launcher$AppClassLoader (id=29)
owns: Class<T> (org.apache.hadoop.security.UserGroupInformation) (id=25)
URLClassLoader$1.run() line: 217
AccessController.doPrivileged(PrivilegedExceptionAction<T>, AccessControlContext) line: not available [native method]
Launcher$AppClassLoader(URLClassLoader).findClass(String) line: 205
Launcher$AppClassLoader(ClassLoader).loadClass(String, boolean) line: 321
Launcher$AppClassLoader.loadClass(String, boolean) line: 294
Launcher$AppClassLoader(ClassLoader).loadClass(String) line: 266
DefaultMetricsSystem.<init>() line: 37
DefaultMetricsSystem.<clinit>() line: 34
UgiInstrumentation.create(Configuration) line: 51
UserGroupInformation.initialize(Configuration) line: 216
UserGroupInformation.ensureInitialized() line: 184
UserGroupInformation.isSecurityEnabled() line: 236
KerberosName.<clinit>() line: 79
UserGroupInformation.initialize(Configuration) line: 209
UserGroupInformation.ensureInitialized() line: 184
UserGroupInformation.isSecurityEnabled() line: 236
UserGroupInformation.getLoginUser() line: 477
UserGroupInformation.getCurrentUser() line: 463
Job(JobContext).<init>(Configuration, JobID) line: 80
Job.<init>(Configuration) line: 50
Job.<init>() line: 46
Program.main(String[]) line: 17
/usr/lib/jvm/java-6-openjdk-amd64/bin/java (Jan 14, 2013 2:42:36 PM)
控制台输出：
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/configuration/Configuration
at org.apache.hadoop.metrics2.lib.DefaultMetricsSystem.<init>(DefaultMetricsSystem.java:37)
at org.apache.hadoop.metrics2.lib.DefaultMetricsSystem.<clinit>(DefaultMetricsSystem.java:34)
at org.apache.hadoop.security.UgiInstrumentation.create(UgiInstrumentation.java:51)
at org.apache.hadoop.security.UserGroupInformation.initialize(UserGroupInformation.java:216)
at org.apache.hadoop.security.UserGroupInformation.ensureInitialized(UserGroupInformation.java:184)
at org.apache.hadoop.security.UserGroupInformation.isSecurityEnabled(UserGroupInformation.java:236)
at org.apache.hadoop.security.KerberosName.<clinit>(KerberosName.java:79)
at org.apache.hadoop.security.UserGroupInformation.initialize(UserGroupInformation.java:209)
at org.apache.hadoop.security.UserGroupInformation.ensureInitialized(UserGroupInformation.java:184)
at org.apache.hadoop.security.UserGroupInformation.isSecurityEnabled(UserGroupInformation.java:236)
at org.apache.hadoop.security.UserGroupInformation.getLoginUser(UserGroupInformation.java:477)
at org.apache.hadoop.security.UserGroupInformation.getCurrentUser(UserGroupInformation.java:463)
at org.apache.hadoop.mapreduce.JobContext.<init>(JobContext.java:80)
at org.apache.hadoop.mapreduce.Job.<init>(Job.java:50)
at org.apache.hadoop.mapreduce.Job.<init>(Job.java:46)
at com.sandbox.hadoop.Program.main(Program.java:18)
Caused by: java.lang.ClassNotFoundException: org.apache.commons.configuration.Configuration
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)
... 16 more