Hadoop jar命令錯誤

Question

在HDFS上執行JAR文件命令時，出現如下錯誤

#hadoop jar WordCountNew.jar WordCountNew /MRInput57/Input-Big.txt /MROutput57
15/11/06 19:46:32 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same.
15/11/06 19:46:32 INFO mapred.JobClient: Cleaning up the staging area hdfs://localhost:8020/var/lib/hadoop-0.20/cache/mapred/mapred/staging/root/.staging/job_201511061734_0003
15/11/06 19:46:32 ERROR security.UserGroupInformation: PriviledgedActionException as:root (auth:SIMPLE) cause:org.apache.hadoop.mapred.FileAlreadyExistsException: Output directory /MRInput57/Input-Big.txt already exists
Exception in thread "main" org.apache.hadoop.mapred.FileAlreadyExistsException: Output directory /MRInput57/Input-Big.txt already exists
    at org.apache.hadoop.mapreduce.lib.output.FileOutputFormat.checkOutputSpecs(FileOutputFormat.java:132)
    at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:921)
    at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:882)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:396)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1278)
    at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:882)
    at org.apache.hadoop.mapreduce.Job.submit(Job.java:526)
    at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:556)
    at MapReduce.WordCountNew.main(WordCountNew.java:114)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:197)


My Driver class Program is as below

    public static void main(String[] args) throws IOException, Exception {
        // Configutation details w. r. t. Job, Jar file
        Configuration conf = new Configuration();
        Job job = new Job(conf, "WORDCOUNTJOB");

        // Setting Driver class
        job.setJarByClass(MapReduceWordCount.class);
        // Setting the Mapper class
        job.setMapperClass(TokenizerMapper.class);
        // Setting the Combiner class
        job.setCombinerClass(IntSumReducer.class);
        // Setting the Reducer class
        job.setReducerClass(IntSumReducer.class);
        // Setting the Output Key class
        job.setOutputKeyClass(Text.class);
        // Setting the Output value class
        job.setOutputValueClass(IntWritable.class);
        // Adding the Input path
        FileInputFormat.addInputPath(job, new Path(args[0]));
        // Setting the output path
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        // System exit strategy
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }

有人可以糾正我的代碼中的問題嗎？

問候普拉納夫

Answer 1

您需要檢查輸出目錄是否不存在，如果存在，請刪除它。 MapReduce無法（或不會）將文件寫入存在的目錄。 它需要創建目錄以確保。

添加：

Path outPath = new Path(args[1]);
FileSystem dfs = FileSystem.get(outPath.toUri(), conf);
if (dfs.exists(outPath)) {
    dfs.delete(outPath, true);
}

Answer 2

在執行程序之前，輸出目錄不應該存在。 在程序中刪除現有目錄或提供新目錄或刪除輸出目錄。

我更喜歡從命令提示符處刪除輸出目錄，然后再從命令提示符處執行程序。

在命令提示符下：

hdfs dfs -rm -r <your_output_directory_HDFS_URL>

從Java：

Chris Gerken code is good enough.

Answer 3

您正在嘗試創建用於存儲輸出的輸出目錄已存在。因此，請嘗試刪除以前相同名稱的目錄或更改輸出目錄的名稱。

Answer 4

正如其他人指出的那樣，由於輸出目錄已經存在而導致出現錯誤，很可能是因為您之前曾嘗試執行此作業。

您可以在運行作業之前刪除現有的輸出目錄，即：

#hadoop fs -rm -r /MROutput57 && \
hadoop jar WordCountNew.jar WordCountNew /MRInput57/Input-Big.txt /MROutput57