java - Hadoop ClassNotFoundException 异常

Question

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 站点下载并使用 Ant 构建来安装 Hadoop。

当我创建作业时，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

Answer 1

您应该添加在 /usr/lib/hadoop-0.xx/lib 中找到的所有 jar 以避免此类类路径问题。

为了给您一个想法，您可以键入 hadoop classpath，它会打印出获取 Hadoop jar 和所需库所需的类路径。

在您的情况下，您缺少 hadoop-common-0.xx.jar，因此您应该将其添加到类路径中，然后就可以开始了。