我试图从simple-yarn-app运行简单的yarn应用程序。但是我的应用程序错误日志中出现以下异常。
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/hadoop/yarn/conf/YarnConfiguration
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2531)
at java.lang.Class.getMethod0(Class.java:2774)
at java.lang.Class.getMethod(Class.java:1663)
at sun.launcher.LauncherHelper.getMainMethod(LauncherHelper.java:494)
at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:486)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.yarn.conf.YarnConfiguration
但是，如果我在所有数据节点上运行“yarn classpath”命令，则会看到以下输出:
/etc/hadoop/conf:/usr/lib/hadoop/lib/*:/usr/lib/hadoop/.//*:/usr/lib/hadoop-hdfs/./:/usr/lib/hadoop-hdfs/lib/*:/usr/lib/hadoop-hdfs/.//*:/usr/lib/hadoop-yarn/lib/*:/usr/lib/hadoop-yarn/.//*:/usr/lib/hadoop-mapreduce/lib/*:/usr/lib/hadoop-mapreduce/.//*:/usr/lib/hadoop-yarn/.//*:/usr/lib/hadoop-yarn/lib/*
它具有应用程序所需的 yarn 客户端，yarn-api，yarn-common和hadoop-common的路径。谁能指出我可能忘记设置正确的类路径的方向。
最佳答案
我发现Hadoop在迭代YarnConfiguration属性时不会解析$ HADOOP_HOME和$ YARN_HOME环境变量。在您的Yarn Client中运行以下命令将打印未解决的配置，例如，
YarnConfiguration conf = new YarnConfiguration()
for (String c : conf.getStrings(
YarnConfiguration.YARN_APPLICATION_CLASSPATH,
YarnConfiguration.DEFAULT_YARN_APPLICATION_CLASSPATH)) {
System.out.println(c);
}
因此，如果您提供yarn.application.classpath属性的完整路径，则可以解决NoClassDefFoundError问题。
<property>
<description>CLASSPATH for YARN applications. A comma-separated list of CLASSPATH entries</description>
<name>yarn.application.classpath</name>
<value>
/etc/hadoop/conf,
/usr/lib/hadoop/*,
/usr/lib/hadoop/lib/*,
/usr/lib/hadoop-hdfs/*,
/usr/lib/hadoop-hdfs/lib/*,
/usr/lib/hadoop-mapreduce/*,
/usr/lib/hadoop-mapreduce/lib/*,
/usr/lib/hadoop-yarn/*,
/usr/lib/hadoop-yarn/lib/*
</value>
</property>
关于hadoop - NoClassDefFoundError用于简单的Yarn应用程序，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/23458385/