hadoop编程：解决eclipse能运行，打包放到集群上ClassNotFoundException:经验总结

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wbj0110 2023-06-05 12:14:26 博主文章分类：Hadoop ©著作权

文章标签 Hadoop java hadoop apache 文章分类 HarmonyOS 后端开发

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本文之所以称之为经验，是因为我们经常碰到莫名其妙的问题，从原理上是说不通的。但是我们却确确实实碰到了。
在刚开始运行的时候，碰到了下文所表示的错误。本想作为经验总结留下来。为了让错误重现，所以又重新操作了一遍。这时候已经换环境，但是环境与原先没做任何的更改，也就是说他们的配置完全是一样的，神奇的是mapreduce执行的完全正确。对于如果碰到下面问题的同学，可以参考。对于原理性的内容，以后在更新。

对于新手，经常遇到，在eclipse中是可以运行的，但是打包放到集群上，不可行，问题如下：

1. Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/hadoop/conf/Configuration
2. at mapreduce.mapreduce.main(mapreduce.java:24)
3. Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.conf.Configuration
4. at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
5. at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
6. at java.security.AccessController.doPrivileged(Native Method)
7. at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
8. at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
9. at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
10. at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
11. ... 1 more

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1. hadoop jar '/home/user/Desktop/mapreduce.jar' mapreduce
2. 14/03/05 05:35:09 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same.
3. 14/03/05 05:35:09 WARN mapred.JobClient: No job jar file set.  User classes may not be found. See JobConf(Class) or JobConf#setJar(String).
4. 14/03/05 05:35:09 INFO input.FileInputFormat: Total input paths to process : 1
5. 14/03/05 05:35:09 INFO util.NativeCodeLoader: Loaded the native-hadoop library
6. 14/03/05 05:35:10 WARN snappy.LoadSnappy: Snappy native library not loaded
7. 14/03/05 05:35:10 INFO mapred.JobClient: Running job: job_201402280238_0011
8. 14/03/05 05:35:11 INFO mapred.JobClient:  map 0% reduce 0%
9. 14/03/05 05:35:25 INFO mapred.JobClient: Task Id : attempt_201402280238_0011_m_000000_0, Status : FAILED
10. java.lang.RuntimeException: java.lang.ClassNotFoundException: mapreduce.mapreduce$MyMapper
11. at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:867)
12. at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199)
13. at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:719)
14. at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
15. at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
16. at java.security.AccessController.doPrivileged(Native Method)
17. at javax.security.auth.Subject.doAs(Subject.java:415)
18. at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
19. at org.apache.hadoop.mapred.Child.main(Child.java:249)
20. Caused by: java.lang.ClassNotFoundException: mapreduce.mapreduce$MyMapper
21. at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
22. at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
23. at java.security.AccessController.doPrivileged(Native Method)
24. at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
25. at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
26. at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
27. at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
28. at java.lang.Class.forName0(Native Method)
29. at java.lang.Class.forName(Class.java:270)
30. at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:820)
31. at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:865)
32. ... 8 more
33. 
34. 14/03/05 05:35:31 INFO mapred.JobClient: Task Id : attempt_201402280238_0011_m_000000_1, Status : FAILED
35. java.lang.RuntimeException: java.lang.ClassNotFoundException: mapreduce.mapreduce$MyMapper
36. at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:867)
37. at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199)
38. at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:719)
39. at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
40. at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
41. at java.security.AccessController.doPrivileged(Native Method)
42. at javax.security.auth.Subject.doAs(Subject.java:415)
43. at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
44. at org.apache.hadoop.mapred.Child.main(Child.java:249)
45. Caused by: java.lang.ClassNotFoundException: mapreduce.mapreduce$MyMapper
46. at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
47. at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
48. at java.security.AccessController.doPrivileged(Native Method)
49. at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
50. at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
51. at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
52. at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
53. at java.lang.Class.forName0(Native Method)
54. at java.lang.Class.forName(Class.java:270)
55. at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:820)
56. at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:865)
57. ... 8 more
58. 
59. 14/03/05 05:35:37 INFO mapred.JobClient: Task Id : attempt_201402280238_0011_m_000000_2, Status : FAILED
60. java.lang.RuntimeException: java.lang.ClassNotFoundException: mapreduce.mapreduce$MyMapper
61. at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:867)
62. at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199)
63. at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:719)
64. at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
65. at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
66. at java.security.AccessController.doPrivileged(Native Method)
67. at javax.security.auth.Subject.doAs(Subject.java:415)
68. at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
69. at org.apache.hadoop.mapred.Child.main(Child.java:249)
70. Caused by: java.lang.ClassNotFoundException: mapreduce.mapreduce$MyMapper
71. at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
72. at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
73. at java.security.AccessController.doPrivileged(Native Method)
74. at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
75. at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
76. at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
77. at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
78. at java.lang.Class.forName0(Native Method)
79. at java.lang.Class.forName(Class.java:270)
80. at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:820)
81. at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:865)
82. ... 8 more
83. 
84. 14/03/05 05:35:49 INFO mapred.JobClient: Job complete: job_201402280238_0011
85. 14/03/05 05:35:49 INFO mapred.JobClient: Counters: 7
86. 14/03/05 05:35:49 INFO mapred.JobClient:   Job Counters 
87. 14/03/05 05:35:49 INFO mapred.JobClient:     SLOTS_MILLIS_MAPS=33927
88. 14/03/05 05:35:49 INFO mapred.JobClient:     Total time spent by all reduces waiting after reserving slots (ms)=0
89. 14/03/05 05:35:49 INFO mapred.JobClient:     Total time spent by all maps waiting after reserving slots (ms)=0
90. 14/03/05 05:35:49 INFO mapred.JobClient:     Launched map tasks=4
91. 14/03/05 05:35:49 INFO mapred.JobClient:     Data-local map tasks=4
92. 14/03/05 05:35:49 INFO mapred.JobClient:     SLOTS_MILLIS_REDUCES=0
93. 14/03/05 05:35:49 INFO mapred.JobClient:     Failed map tasks=1

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我们需要分析上面是什么错误，其实就是找不到类，为什么会找不到类，是我们打包问题吗？是因为没有环境不正确吗？
是的，这两方面可能都有问题，那么该如何解决
首先来看看我们是如何打包的：

1.单击map.java文件，弹出快捷菜单，选择Export。

2.第一步之后，我们会看到下面，选择Java下面的JAR file。

3.我们单击Next，进入JAR Export选择我们要打的包即可。

4.单击next下一步，然后在下一步，咱们会看到主类，我们选择主类到Main class

5.选择主类到Main class，我们会看到mapreduce.map，其实这是包名.类型

6.到这一步，单击finish。我们看到了这个包。并且看到它的大小。

打包完毕，我们放到集群上运行：
出现下面情况
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/hadoop/conf/Configuration
。
解决：
对于上面我们是否可以采用另外一种方法：答案是可以的。
就是我们，打成java运行jar包，是绝对可行的。