1.用hadoop的eclipse插件下M/R程序的时候，有时候会报
Exception in thread "main" java.lang.IllegalArgumentException: Pathname /D:/hadoop/hadoop-2.2.0/hadoop-2.2.0/share/hadoop/mapreduce/hadoop-mapreduce-client-core-2.2.0.jar from hdfs://uat84:49100/D:/hadoop/hadoop-2.2.0/hadoop-2.2.0/share/hadoop/mapreduce/hadoop-mapreduce-client-core-2.2.0.jar is not a valid DFS filename
服务器下报错是：
[2014-05-11 19:09:40,019] ERROR [main] (UserGroupInformation.java:1494) org.apache.hadoop.security.UserGroupInformation - PriviledgedActionException as:hadoop (auth:SIMPLE) cause:java.io.FileNotFoundException: File does not exist: hdfs://uat84:49100/usr/local/bigdata/hbase/lib/hadoop-common-2.2.0.jar
Exception in thread "main" java.io.FileNotFoundException: File does not exist: hdfs://uat84:49100/usr/local/bigdata/hbase/lib/hadoop-common-2.2.0.jar
at org.apache.hadoop.hdfs.DistributedFileSystem$17.doCall(DistributedFileSystem.java:1110)
at org.apache.hadoop.hdfs.DistributedFileSystem$17.doCall(DistributedFileSystem.java:1102)
at org.apache.hadoop.fs.FileSystemLinkResolver.resolve(FileSystemLinkResolver.java:81)
at org.apache.hadoop.hdfs.DistributedFileSystem.getFileStatus(DistributedFileSystem.java:1102)
at org.apache.hadoop.mapreduce.filecache.ClientDistributedCacheManager.getFileStatus(ClientDistributedCacheManager.java:288)
at org.apache.hadoop.mapreduce.filecache.ClientDistributedCacheManager.getFileStatus(ClientDistributedCacheMa
这是tm的什么fucking错误！！拿着别人正确的程序一点一点查，发现是因为有这句话：
Configuration conf = new Configuration();
conf.set("fs.default.name", "hdfs://uat84:49100");
这是什么意思呢，就是说，你如果是本地跑，就是不引入mapred-site,yarn-site,core-site这些配置文件，那么这个地方也不要设置，因为你是在本地跑M/R程序，(fs.default.name默认值是file:///，表示本地文件系统)这个地方却又告诉hadoop，需要的jar包从hdfs中取，当然会报以上的问题。那么，在本地跑直接去掉这句话就ok了。
反之，如果你是提交到集群，引入了mapred-site,yarn-site，却没有引入core-site，也没有设置fs.default.name,那么，因为不知道namenode的地址，无法将job.jar提交到hadoop集群上，因此会报如下错误：
[2014-05-13 16:35:03,625] INFO [main] (Job.java:1358) org.apache.hadoop.mapreduce.Job - Job job_1397132528617_2814 failed with state FAILED due to: Application application_1397132528617_2814 failed 2 times due to AM Container for appattempt_1397132528617_2814_000002 exited with exitCode: -1000 due to: File file:/tmp/hadoop-yarn/staging/hadoop/.staging/job_1397132528617_2814/job.jar does not exist
.Failing this attempt.. Failing the application.
牛不牛！因此我们只要告诉hadoop我们的namenode地址就可以了。引入core-site或是设置
fs.default.name 都是一样的
2.在跑hdfs到hbase的代码的时候，报出如下错误：
java.lang.RuntimeException: java.lang.NoSuchMethodException: CopyOfHive2Hbase$Redcuer.<init>()
at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:131)
at org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:629)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:405)
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:445)
Caused by: java.lang.NoSuchMethodException: CopyOfHive2Hbase$Redcuer.<init>()
at java.lang.Class.getConstructor0(Class.java:2715)
at java.lang.Class.getDeclaredConstructor(Class.java:1987)
at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:125)
... 3 more
fucking man啊，光看这个，谁能看出来Rducer哪里写的有问题！我服他了！！！
也是对比人家正确的代码，一点一点看，发现，原来是因为我的reduce方法不是static的！！！！
想死的心都有了
public static class Redcuer extends TableReducer<Text, Text, NullWritable> {
private String[] columname ;
public void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
System.out.println("!!!!!!!!!!!!!!!!!!!reduce!!!!!!!" + key.toString());
Put put = new Put(Bytes.toBytes("test1234"));
put.add(Bytes.toBytes("fc"), Bytes.toBytes("1"), Bytes.toBytes("2"));
context.write(NullWritable.get(), put);
}
}
