Question

在HDFS上执行JAR文件命令时出现错误，如下所示

#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);
    }

有人可以在我的代码中纠正这个问题吗？

此致 Pranav

Answer 1

您需要检查输出目录是否已存在，如果存在，则将其删除。 MapReduce不能（或不会）将文件写入存在的目录。它需要创建目录以确保。

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

在执行程序之前，输出目录不应该存在。删除现有目录或提供新目录或删除程序中的输出目录。

我更喜欢在从命令提示符执行程序之前从命令提示符删除输出目录。

从命令提示符：

hdfs dfs -rm -r <your_output_directory_HDFS_URL>

来自java：

Chris Gerken code is good enough.

Answer 3

您尝试创建存储输出的输出目录已经存在。所以尝试删除以前的同名目录或更改输出目录的名称。

Answer 4

正如其他人所说，您收到错误是因为输出目录已经存在，很可能是因为您之前尝试过执行此作业。

您可以在运行作业之前删除现有的输出目录，即：

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

Hadoop jar命令错误

4 个答案: