HADOOP - 1.2.1稳定的字数统计实例 [英] HADOOP - Word Count Example for 1.2.1 Stable

问题描述

我正在通过hadoop 1.2.1的一个字数计算例子。但是有些东西一定会改变的，因为我似乎无法使它工作。

这是我的Reduce类：

  public static class Reduce extends Reducer< WritableComparable，Writable，WritableComparable，Writable> {
 $ b $ public void reduce（WritableComparable key，
 Iterator< Writable> values，
 OutputCollector< WritableComparable，NullWritable>输出，
 Reporter记者）抛出IOException {
 
 output.collect（key，NullWritable.get（））; 
 
} 
 
} 
  

而我的主要函数：

  public static void main（String [] args）throws Exception {
 
 JobConf jobConf =新的JobConf（MapDemo.class）; 
 
 jobConf.setNumMapTasks（10）; 
 jobConf.setNumReduceTasks（1）; 
 
 jobConf.setJobName（MapDemo）; 
 
 jobConf.setOutputKeyClass（Text.class）; 
 jobConf.setOutputValueClass（NullWritable.class）; 
 
 jobConf.setMapperClass（Map.class）; 
 jobConf.setReducerClass（Reduce.class）; 
 
 jobConf.setInputFormat（TextInputFormat.class）; 
 jobConf.setOutputFormat（TextOutputFormat.class）; 
 
 FileInputFormat.setInputPaths（jobConf，new Path（args [0]））; 
 FileOutputFormat.setOutputPath（jobConf，new Path（args [1]））; 
 
 JobClient.runJob（jobConf）; 
} 
  

我的IDE告诉我存在一个错误，由Maven证实： p>

  [错误]编译错误：
 [信息] --------------- ---------------------------------------------- 
 [错误] com / example / mapreduce / MapDemo.java：[71,16]类org.apache.hadoop.mapred.JobConf中的方法setReducerClass不能应用于给定的类型; 
需要：java.lang.Class<？扩展org.apache.hadoop.mapred.Reducer> 
 found：java.lang.Class< com.example.mapreduce.MapDemo.Reduce> 
 reason：实际参数java.lang.Class< com.example.mapreduce.MapDemo.Reduce>无法转换为java.lang.Class<扩展org.apache.hadoop.mapred.Reducer>通过方法调用转换
 [INFO] 1错误
 [INFO] ------------------------------ ------------------------------- 
 [信息] ------------ -------------------------------------------------- ---------- 
 [INFO] BUILD FAILURE 
 [INFO] ------------------------ ------------------------------------------------ 
 [INFO]总时间：1.679s 
 [信息]完成时间：周一9月16日09:23:08 PDT 2013 
 [INFO]最终记忆：17M / 202M 
 [信息] -------------------------------------------------- ---------------------- 
 [错误]无法执行目标org.apache.maven.plugins：maven-compiler-plugin：3.0：compile （default-compile）：编译失败
 [错误] com / example / mapreduce / MapDemo.java：[71,16]类org.apache.hadoop.mapred.JobConf中的方法setReducerClass不能应用于给定类型; 
 [错误] required：java.lang.Class<？扩展org.apache.hadoop.mapred.Reducer> 
 [错误] found：java.lang.Class< com.example.mapreduce.MapDemo.Reduce> 
  

我相信网上的数字例子在1.2.1中已经过期。我该如何解决？有没有人有一个链接到一个工作1.2.1字数java源？

解决方案

你跟随哪个链接？我从来没有见过这样的WC。但是，无论你使用的是旧API，它们肯定是过时的。我怀疑你是否正确地遵守了它。

这应该可以工作：

  public class WordCount {
 / ** 
 * WordCount的地图类。 
 * / 
 public static class TokenCounterMapper extends 
 Mapper< Object，Text，Text，IntWritable> {
 
 private static static IntWritable one = new IntWritable（1）; 
私人文字=新文字（）; 
 $ b $ public void map（Object key，Text value，Context context）
 throws IOException，InterruptedException {
 
 StringTokenizer itr = new StringTokenizer（value.toString（）） ; 
 while（itr.hasMoreTokens（））{
 word.set（itr.nextToken（））; 
 context.write（word，one）; 
 
 
 
 $ b / ** 
 * WordCount的缩减器类
 * / 
公共静态类TokenCounterReducer扩展
 Reducer<文本，IntWritable，文本，IntWritable> {
 public void reduce（Text key，Iterable< IntWritable> values，
 Context context）throws IOException，InterruptedException {
 int sum = 0; （IntWritable value：values）
（
 sum + = value.get（）; 
} 
 context.write（key，new IntWritable（sum））; 
} 
} 
 
 / ** 
 *主要入口点。 
 * / 
 public static void main（String [] args）throws Exception {
 Configuration conf = new Configuration（）; 
 conf.addResource（new Path（/ Users / miqbal1 / hadoop-eco / hadoop-1.1.2 / conf / core-site.xml））; 
 conf.addResource（new Path（/ Users / miqbal1 / hadoop-eco / hadoop-1.1.2 / conf / hdfs-site.xml））; 
 conf.set（fs.default.name，hdfs：// localhost：9000）; 
 conf.set（mapred.job.tracker，localhost：9001）; 
工作职位=新职位（conf，WordCount）; 
 job.setJarByClass（WordCount.class）; 
 job.setMapperClass（TokenCounterMapper.class）; 
 job.setReducerClass（TokenCounterReducer.class）; 
 job.setNumReduceTasks（2）; 
 job.setOutputKeyClass（Text.class）; 
 job.setOutputValueClass（IntWritable.class）; 
 FileInputFormat.addInputPath（job，new Path（/ inputs / demo.txt））; 
 FileOutputFormat.setOutputPath（job，new Path（/ outputs / 1111223））; 
 System.exit（job.waitForCompletion（true）？0：1）; 
 
 
 $ / code $ 
 
 
 
几乎没有观察到：
 
 
 
 
 
由于我看到 NullWritable 从Reducer发出，因此您没有发出任何计数。它只会发出没有任何计数的密钥。
 
 
使用正确类型输入和输出键/值。
 > 
 
使用新API 。它更干净，更好。
 
 
 
I am working through a word count example for hadoop 1.2.1. But something must have changed, because I cant seem to get it to work.

Here is my Reduce class:
public static class Reduce extends Reducer<WritableComparable, Writable, WritableComparable, Writable> {

    public void reduce(WritableComparable key,
                       Iterator<Writable> values,
                       OutputCollector<WritableComparable, NullWritable> output,
                       Reporter reporter) throws IOException {

        output.collect(key, NullWritable.get());

    }

}
And my main function:
public static void main(String[] args) throws Exception {

    JobConf jobConf = new JobConf(MapDemo.class);

    jobConf.setNumMapTasks(10);
    jobConf.setNumReduceTasks(1);

    jobConf.setJobName("MapDemo");

    jobConf.setOutputKeyClass(Text.class);
    jobConf.setOutputValueClass(NullWritable.class);

    jobConf.setMapperClass(Map.class);
    jobConf.setReducerClass(Reduce.class);

    jobConf.setInputFormat(TextInputFormat.class);
    jobConf.setOutputFormat(TextOutputFormat.class);

    FileInputFormat.setInputPaths(jobConf, new Path(args[0]));
    FileOutputFormat.setOutputPath(jobConf, new Path(args[1]));

    JobClient.runJob(jobConf);
}
My IDE is telling me there is an error, corroborated by Maven:
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] com/example/mapreduce/MapDemo.java:[71,16] method setReducerClass in class org.apache.hadoop.mapred.JobConf cannot be applied to given types;
required: java.lang.Class<? extends org.apache.hadoop.mapred.Reducer>
found: java.lang.Class<com.example.mapreduce.MapDemo.Reduce>
reason: actual argument java.lang.Class<com.example.mapreduce.MapDemo.Reduce> cannot be converted to java.lang.Class<? extends org.apache.hadoop.mapred.Reducer> by method invocation conversion
[INFO] 1 error
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.679s
[INFO] Finished at: Mon Sep 16 09:23:08 PDT 2013
[INFO] Final Memory: 17M/202M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.0:compile (default-compile) on project inventory: Compilation failure
[ERROR] com/example/mapreduce/MapDemo.java:[71,16] method setReducerClass in class org.apache.hadoop.mapred.JobConf cannot be applied to given types;
[ERROR] required: java.lang.Class<? extends org.apache.hadoop.mapred.Reducer>
[ERROR] found: java.lang.Class<com.example.mapreduce.MapDemo.Reduce>
I believe the word count examples online are out of date for 1.2.1.  How do I fix this?  Does anyone have a link to a working 1.2.1 word count java source?
解决方案
Which link have you followed? I have never seen this kind of WC. But whatever you have followed is definitely outdated since it is making use of the old API. And I doubt if you have followed it properly. 

This should work :
public class WordCount {
    /**
     * The map class of WordCount.
     */
    public static class TokenCounterMapper extends
            Mapper<Object, Text, Text, IntWritable> {

        private final static IntWritable one = new IntWritable(1);
        private Text word = new Text();

        public void map(Object key, Text value, Context context)
                throws IOException, InterruptedException {              

            StringTokenizer itr = new StringTokenizer(value.toString());
            while (itr.hasMoreTokens()) {
                word.set(itr.nextToken());
                context.write(word, one);
            }
        }
    }

    /**
     * The reducer class of WordCount
     */
    public static class TokenCounterReducer extends
            Reducer<Text, IntWritable, Text, IntWritable> {
        public void reduce(Text key, Iterable<IntWritable> values,
                Context context) throws IOException, InterruptedException {
            int sum = 0;
            for (IntWritable value : values) {
                sum += value.get();
            }
            context.write(key, new IntWritable(sum));
        }
    }

    /**
     * The main entry point.
     */
    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        conf.addResource(new Path("/Users/miqbal1/hadoop-eco/hadoop-1.1.2/conf/core-site.xml"));
        conf.addResource(new Path("/Users/miqbal1/hadoop-eco/hadoop-1.1.2/conf/hdfs-site.xml"));
        conf.set("fs.default.name", "hdfs://localhost:9000");
        conf.set("mapred.job.tracker", "localhost:9001");
        Job job = new Job(conf, "WordCount");
        job.setJarByClass(WordCount.class);
        job.setMapperClass(TokenCounterMapper.class);
        job.setReducerClass(TokenCounterReducer.class);
        job.setNumReduceTasks(2);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        FileInputFormat.addInputPath(job, new Path("/inputs/demo.txt"));
        FileOutputFormat.setOutputPath(job, new Path("/outputs/1111223"));
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}
Few observations to make :


You are not emitting any count as I can see NullWritable getting emitted from your Reducer. It will just emit the key without any count.
Use proper types for your input and output keys/values.
Use the new API. It is cleaner and better.


                        
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