首页 \ 问答 \ 无法在mapper，MapReduce中访问hashmap(Can't access hashmap in mapper, MapReduce)

无法在mapper，MapReduce中访问hashmap(Can't access hashmap in mapper, MapReduce)

 我想使用另一个文件中定义的字典（csv）替换mapper中输入数据的值。 所以我试着将csv数据放到HashMap中并在mapper中引用它。 
 

 下面的java代码和csv是我程序的简化版本。 此代码适用于我的本地环境 （Mac OS X，伪分布式模式），但不适用于我的EC2实例（ubuntu，伪分布式模式） 。 
 

 详细地说，我在这个过程中得到了这个标准： 
 

cat:4
human:2
flamingo:1

 

 这意味着文件读取器成功地将csv数据放入HashMap。 
 

 然而，映射器没有映射任何内容因此我在EC2环境中得到空输出，尽管它映射了3 *（输入文件的行数）元素并在本地生成以下内容： 
 

test,cat
test,flamingo
test,human

 

 有没有人有答案或提示？ 
 

 Test.java 
 

import java.io.IOException;
import java.util.StringTokenizer;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.DataInput; 
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.mapreduce.RecordWriter;
import org.apache.hadoop.io.WritableUtils;

public class Test {

  public static HashMap<String, Integer> map  = new HashMap<String, Integer>();

  public static class Mapper1 extends Mapper<LongWritable, Text, Text, Text> {
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
      for(Map.Entry<String, Integer> e : map.entrySet()) {
        context.write(new Text(e.getKey()), new Text("test"));
      }
    }
  }

  public static class Reducer1 extends Reducer<Text, Text, Text, Text> {
    @Override
    protected void reduce(Text key, Iterable<Text> vals, Context context) throws IOException, InterruptedException {
      context.write(new Text("test"), key);
    }
  }

  public static class CommaTextOutputFormat extends TextOutputFormat<Text, Text> {
    @Override
    public RecordWriter<Text, Text> getRecordWriter(TaskAttemptContext job) throws IOException, InterruptedException {
      Configuration conf = job.getConfiguration();
      String extension = ".txt";
      Path file = getDefaultWorkFile(job, extension);
      FileSystem fs = file.getFileSystem(conf);
      FSDataOutputStream fileOut = fs.create(file, false);
      return new LineRecordWriter<Text, Text>(fileOut, ",");
    }
  }

  public static void get_list(String list_path){
    try {
      FileReader fr = new FileReader(list_path);
      BufferedReader br = new BufferedReader(fr);
      String line = null, name = null;
      int leg = 0;

      while ((line = br.readLine()) != null) {
        if (!line.startsWith("name") && !line.trim().isEmpty()) {
          String[] name_leg = line.split(",", 0);
          name = name_leg[0];
          leg = Integer.parseInt(name_leg[1]);
          map.put(name, leg);
        }
      }
      br.close();
    }
    catch(IOException ex) {
      System.err.println(ex.getMessage());
      ex.printStackTrace();
    }

    for(Map.Entry<String, Integer> e : map.entrySet()) {
      System.out.println(e.getKey() + ":" + e.getValue());
    }
  }

  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();

    if (args.length != 3) {
      System.err.println(
        "Need 3 arguments: <input dir> <output base dir> <list path>");
      System.exit(1);
    }

    get_list(args[2]);
    Job job = Job.getInstance(conf, "test");

    job.setJarByClass(Test.class);
    job.setMapperClass(Mapper1.class);
    job.setReducerClass(Reducer1.class);
    job.setNumReduceTasks(1);
    job.setInputFormatClass(TextInputFormat.class);

    // mapper output
    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(Text.class);

    // reducer output
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(Text.class);

    // formtter
    job.setOutputFormatClass(CommaTextOutputFormat.class);

    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));

    if(!job.waitForCompletion(true)){
      System.exit(1);
    }

    System.out.println("All Finished");
    System.exit(0);
  }
}

 

 list.csv（args [2]） 
 

name,legs
cat,4
human,2
flamingo,1

 

 ================================= 
 

 我参考@Rahul Sharma的回答并修改我的代码如下。 然后我的代码在两种环境中都有效。 
 

 非常感谢@Rahul Sharma和@Serhiy的精确答案和有用的评论。 
 

 Test.java 
 

import java.io.IOException;
import java.util.StringTokenizer;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.DataInput; 
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.net.URI;
import java.io.InputStreamReader;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.mapreduce.RecordWriter;
import org.apache.hadoop.io.WritableUtils;

public class Test {

  public static HashMap<String, Integer> map  = new HashMap<String, Integer>();

  public static class Mapper1 extends Mapper<LongWritable, Text, Text, Text> {

    @Override
    protected void setup(Context context) throws IOException, InterruptedException {
      URI[] files = context.getCacheFiles();
      Path list_path = new Path(files[0]);

      try {
        FileSystem fs = list_path.getFileSystem(context.getConfiguration());
        BufferedReader br = new BufferedReader(new InputStreamReader(fs.open(list_path)));
        String line = null, name = null;
        int leg = 0;

        while ((line = br.readLine()) != null) {
          if (!line.startsWith("name") && !line.trim().isEmpty()) {
            String[] name_leg = line.split(",", 0);
            name = name_leg[0];
            leg = Integer.parseInt(name_leg[1]);
            map.put(name, leg);
          }
        }
        br.close();
      }
      catch(IOException ex) {
        System.err.println(ex.getMessage());
        ex.printStackTrace();
      }

      for(Map.Entry<String, Integer> e : map.entrySet()) {
        System.out.println(e.getKey() + ":" + e.getValue());
      }
    }

    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
      for(Map.Entry<String, Integer> e : map.entrySet()) {
        context.write(new Text(e.getKey()), new Text("test"));
      }
    }

  }

  public static class Reducer1 extends Reducer<Text, Text, Text, Text> {
    @Override
    protected void reduce(Text key, Iterable<Text> vals, Context context) throws IOException, InterruptedException {
      context.write(new Text("test"), key);
    }
  }

  // Writer
  public static class CommaTextOutputFormat extends TextOutputFormat<Text, Text> {
    @Override
    public RecordWriter<Text, Text> getRecordWriter(TaskAttemptContext job) throws IOException, InterruptedException {
      Configuration conf = job.getConfiguration();
      String extension = ".txt";
      Path file = getDefaultWorkFile(job, extension);
      FileSystem fs = file.getFileSystem(conf);
      FSDataOutputStream fileOut = fs.create(file, false);
      return new LineRecordWriter<Text, Text>(fileOut, ",");
    }
  }

  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();

    if (args.length != 3) {
      System.err.println(
        "Need 3 arguments: <input dir> <output base dir> <list path>");
      System.exit(1);
    }

    Job job = Job.getInstance(conf, "test");
    job.addCacheFile(new Path(args[2]).toUri());

    job.setJarByClass(Test.class);
    job.setMapperClass(Mapper1.class);
    job.setReducerClass(Reducer1.class);
    job.setNumReduceTasks(1);
    job.setInputFormatClass(TextInputFormat.class);

    // mapper output
    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(Text.class);

    // reducer output
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(Text.class);

    // formtter
    job.setOutputFormatClass(CommaTextOutputFormat.class);

    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));

    if(!job.waitForCompletion(true)){
      System.exit(1);
    }

    System.out.println("All Finished");
    System.exit(0);
  }
}


I'd like to replace values of input data in my mapper, using dictionalies(csv) defined in another file. So I tried to put the csv data to HashMap and refer it in the mapper.
 

The java code and csv below are simplified version of my program. This code works in my local environment(Mac OS X, pseudo-distributed mode), but doesn't in my EC2 instance(ubuntu, pseudo-distributed mode).
 

In detail, I got this stdout in process:
 

cat:4
human:2
flamingo:1

 

this means the filereader successfully put csv data into HashMap.
 

However the mapper mapped nothing and therefore I got empty output in the EC2 environment, although it mapped 3 * (the number of lines of the input file) elements and generated the following in the local:
 

test,cat
test,flamingo
test,human

 

Does anyone have answers or hints? 
 

Test.java
 

import java.io.IOException;
import java.util.StringTokenizer;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.DataInput; 
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.mapreduce.RecordWriter;
import org.apache.hadoop.io.WritableUtils;

public class Test {

  public static HashMap<String, Integer> map  = new HashMap<String, Integer>();

  public static class Mapper1 extends Mapper<LongWritable, Text, Text, Text> {
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
      for(Map.Entry<String, Integer> e : map.entrySet()) {
        context.write(new Text(e.getKey()), new Text("test"));
      }
    }
  }

  public static class Reducer1 extends Reducer<Text, Text, Text, Text> {
    @Override
    protected void reduce(Text key, Iterable<Text> vals, Context context) throws IOException, InterruptedException {
      context.write(new Text("test"), key);
    }
  }

  public static class CommaTextOutputFormat extends TextOutputFormat<Text, Text> {
    @Override
    public RecordWriter<Text, Text> getRecordWriter(TaskAttemptContext job) throws IOException, InterruptedException {
      Configuration conf = job.getConfiguration();
      String extension = ".txt";
      Path file = getDefaultWorkFile(job, extension);
      FileSystem fs = file.getFileSystem(conf);
      FSDataOutputStream fileOut = fs.create(file, false);
      return new LineRecordWriter<Text, Text>(fileOut, ",");
    }
  }

  public static void get_list(String list_path){
    try {
      FileReader fr = new FileReader(list_path);
      BufferedReader br = new BufferedReader(fr);
      String line = null, name = null;
      int leg = 0;

      while ((line = br.readLine()) != null) {
        if (!line.startsWith("name") && !line.trim().isEmpty()) {
          String[] name_leg = line.split(",", 0);
          name = name_leg[0];
          leg = Integer.parseInt(name_leg[1]);
          map.put(name, leg);
        }
      }
      br.close();
    }
    catch(IOException ex) {
      System.err.println(ex.getMessage());
      ex.printStackTrace();
    }

    for(Map.Entry<String, Integer> e : map.entrySet()) {
      System.out.println(e.getKey() + ":" + e.getValue());
    }
  }

  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();

    if (args.length != 3) {
      System.err.println(
        "Need 3 arguments: <input dir> <output base dir> <list path>");
      System.exit(1);
    }

    get_list(args[2]);
    Job job = Job.getInstance(conf, "test");

    job.setJarByClass(Test.class);
    job.setMapperClass(Mapper1.class);
    job.setReducerClass(Reducer1.class);
    job.setNumReduceTasks(1);
    job.setInputFormatClass(TextInputFormat.class);

    // mapper output
    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(Text.class);

    // reducer output
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(Text.class);

    // formtter
    job.setOutputFormatClass(CommaTextOutputFormat.class);

    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));

    if(!job.waitForCompletion(true)){
      System.exit(1);
    }

    System.out.println("All Finished");
    System.exit(0);
  }
}

 

list.csv (args[2])
 

name,legs
cat,4
human,2
flamingo,1

 

=================================
 

I refer to @Rahul Sharma 's answer and modifiy my code as below. Then my code works in the both environments. 
 

Thank you very much @Rahul Sharma and @Serhiy for your precise answer and useful comments.
 

Test.java
 

import java.io.IOException;
import java.util.StringTokenizer;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.DataInput; 
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.net.URI;
import java.io.InputStreamReader;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.mapreduce.RecordWriter;
import org.apache.hadoop.io.WritableUtils;

public class Test {

  public static HashMap<String, Integer> map  = new HashMap<String, Integer>();

  public static class Mapper1 extends Mapper<LongWritable, Text, Text, Text> {

    @Override
    protected void setup(Context context) throws IOException, InterruptedException {
      URI[] files = context.getCacheFiles();
      Path list_path = new Path(files[0]);

      try {
        FileSystem fs = list_path.getFileSystem(context.getConfiguration());
        BufferedReader br = new BufferedReader(new InputStreamReader(fs.open(list_path)));
        String line = null, name = null;
        int leg = 0;

        while ((line = br.readLine()) != null) {
          if (!line.startsWith("name") && !line.trim().isEmpty()) {
            String[] name_leg = line.split(",", 0);
            name = name_leg[0];
            leg = Integer.parseInt(name_leg[1]);
            map.put(name, leg);
          }
        }
        br.close();
      }
      catch(IOException ex) {
        System.err.println(ex.getMessage());
        ex.printStackTrace();
      }

      for(Map.Entry<String, Integer> e : map.entrySet()) {
        System.out.println(e.getKey() + ":" + e.getValue());
      }
    }

    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
      for(Map.Entry<String, Integer> e : map.entrySet()) {
        context.write(new Text(e.getKey()), new Text("test"));
      }
    }

  }

  public static class Reducer1 extends Reducer<Text, Text, Text, Text> {
    @Override
    protected void reduce(Text key, Iterable<Text> vals, Context context) throws IOException, InterruptedException {
      context.write(new Text("test"), key);
    }
  }

  // Writer
  public static class CommaTextOutputFormat extends TextOutputFormat<Text, Text> {
    @Override
    public RecordWriter<Text, Text> getRecordWriter(TaskAttemptContext job) throws IOException, InterruptedException {
      Configuration conf = job.getConfiguration();
      String extension = ".txt";
      Path file = getDefaultWorkFile(job, extension);
      FileSystem fs = file.getFileSystem(conf);
      FSDataOutputStream fileOut = fs.create(file, false);
      return new LineRecordWriter<Text, Text>(fileOut, ",");
    }
  }

  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();

    if (args.length != 3) {
      System.err.println(
        "Need 3 arguments: <input dir> <output base dir> <list path>");
      System.exit(1);
    }

    Job job = Job.getInstance(conf, "test");
    job.addCacheFile(new Path(args[2]).toUri());

    job.setJarByClass(Test.class);
    job.setMapperClass(Mapper1.class);
    job.setReducerClass(Reducer1.class);
    job.setNumReduceTasks(1);
    job.setInputFormatClass(TextInputFormat.class);

    // mapper output
    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(Text.class);

    // reducer output
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(Text.class);

    // formtter
    job.setOutputFormatClass(CommaTextOutputFormat.class);

    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));

    if(!job.waitForCompletion(true)){
      System.exit(1);
    }

    System.out.println("All Finished");
    System.exit(0);
  }
}


原文：
更新时间：2021-09-10 08:09

最满意答案

 您提供的示例在HTML和XHTML中无效。 除非启用了脚本， 否则当前建议不提供包含样式表的方法。 
 

 一般来说，你应该避免<noscript> 。 从有效的东西开始，然后在它上面构建。 
 

 在这种情况下，您可以为非JS客户端编写样式表，然后： 
 

<body>
<script type="text/javascript">document.body.className += ' js';</script>

 

 ...并包含特定于JS的其他规则集： 
 

body.js foo {
}

 

 或者，您可以执行以下操作： 
 

<link href="css/stylenojs.css" rel="stylesheet" type="text/css" id="nojscss" />

 

 和 
 

var nojscss = document.getElementById('nojscss');
nojscss.parentNode.removeChild(nojscss);


The example you give is invalid in HTML as well as XHTML. No current recommendation provides a way to include a stylesheet unless scripting is enabled.
 

In general, you should avoid <noscript>. Start with something that works, and then build on it. 
 

In this case, you could write your stylesheet for non-JS clients, then:
 

<body>
<script type="text/javascript">document.body.className += ' js';</script>

 

… and include additional rule-sets specific to JS being enabled with:
 

body.js foo {
}

 

Alternatively, you could do something like:
 

<link href="css/stylenojs.css" rel="stylesheet" type="text/css" id="nojscss" />

 

and
 

var nojscss = document.getElementById('nojscss');
nojscss.parentNode.removeChild(nojscss);

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