在Ubuntu 16.04中使用JAVA中的MapReduce在文本文件中搜索给定单词

Question

我必须做一个项目来查找给定的单词（字符串）。 该字符串将由用户输入。 然后在存储在HDFS中的特定文本文件中查找单词的出现。 输出应该表明单词字符串的存在。

package stringSearchJob;
import java.io.IOException;
import java.util.Scanner;

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.mapred.JobClient;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class StringSearch{
    public static void main(String argv[]) throws Exception {
        try {
            if (argv.length<3) {
                System.err.println("Give the input/ output/ keyword!");
                return;
            }
            JobConf conf = new JobConf(StringSearch.class);
            Job job = new Job(conf,"StringSearch");

            FileInputFormat.addInputPath(job, new Path(argv[0]));
            FileOutputFormat.setOutputPath(job, new Path(argv[1]));
            conf.set("search", argv[2]);

            job.setJarByClass(StringSearch.class);
            job.setMapperClass(WordMapper.class);
            job.setNumReduceTasks(0);

            job.setMapOutputKeyClass(Text.class);
            job.setMapOutputValueClass(IntWritable.class);

            job.setOutputKeyClass(Text.class);
            job.setOutputValueClass(IntWritable.class);

            JobClient.runJob(conf); 
            job.waitForCompletion(true);
       }    
       catch (Exception e) {
           e.printStackTrace();
       }
  }    
  public static class WordMapper extends Mapper<LongWritable, Text, Text, IntWritable>{ 
    @Override 
    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            try {
                Configuration conf = context.getConfiguration();
                String search = conf.get("search");
                String line = value.toString();
                Scanner scanner = new Scanner(line);
                while (scanner.hasNext()) {
                    if (line.contains(search)) {
                        String line1 = scanner.next();
                        context.write(new Text(line1), new IntWritable(1));
                    }
                }
                scanner.close();
            }
            catch (IOException e){
                e.printStackTrace();
            }
            catch (InterruptedException e){
                e.printStackTrace();
            }
        }    
    }    
}

我的代码错了吗？ 因为我在Ubuntu-16.04 Terminal上获得的输出不正确。 我遵循的步骤如下：

1. 拧上上面的代码后，我将其导出到名为StringSearch.jar的Runnable JAR文件中。 类名是StringSearch 。

2. 现在，在终端上，我编写了以下命令：

    hadoop fs -mkdir /user hadoop fs -mkdir /user/hduser hadoop fs -mkdir /user/hduser/StringSearch hadoop fs -mkdir Stringsearch/input hadoop -fs -copyFromLocal sample.txt StringSearch/input hadoop jar StringSearchNew.jar StringSearch /user/hduser/StringSearch/input user/hduser/StringSearch/output 'Lord' 

3. 而且我得到的错误如下。

    17/08/20 19:17:35 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable 17/08/20 19:17:41 INFO Configuration.deprecation: session.id is deprecated. Instead, use dfs.metrics.session-id 17/08/20 19:17:41 INFO jvm.JvmMetrics: Initializing JVM Metrics with processName=JobTracker, sessionId= 17/08/20 19:17:41 INFO jvm.JvmMetrics: Cannot initialize JVM Metrics with processName=JobTracker, sessionId= - already initialized Exception in thread "main" org.apache.hadoop.mapred.InvalidJobConfException: Output directory not set in JobConf. at org.apache.hadoop.mapred.FileOutputFormat.checkOutputSpecs(FileOutputFormat.java:117) at org.apache.hadoop.mapreduce.JobSubmitter.checkSpecs(JobSubmitter.java:268) at org.apache.hadoop.mapreduce.JobSubmitter.submitJobInternal(JobSubmitter.java:139) at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1290) at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1287) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:422) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1698) at org.apache.hadoop.mapreduce.Job.submit(Job.java:1287) at org.apache.hadoop.mapred.JobClient$1.run(JobClient.java:575) at org.apache.hadoop.mapred.JobClient$1.run(JobClient.java:570) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:422) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1698) at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:570) at org.apache.hadoop.mapred.JobClient.submitJob(JobClient.java:561) at org.apache.hadoop.mapred.JobClient.runJob(JobClient.java:870) at stringSearchJob.StringSearch.main(StringSearch.java:43) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.hadoop.util.RunJar.run(RunJar.java:221) at org.apache.hadoop.util.RunJar.main(RunJar.java:136) 

我基本上了解了如何仅从Internet使用Hadoop MapReduce。 当我尝试了所有其他类似的答案后，试图用JAVA制作程序时，它没有给出输出。 我是Hadoop的新手，因此，如果您能帮助我解决这个问题，将会对您有所帮助。 我不明白这里有什么问题！

---

阅读答案后，我编辑了代码并得到以下错误：

    17/08/24 05:01:30 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
    Exception in thread "main" java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.eclipse.jdt.internal.jarinjarloader.JarRsrcLoader.main(JarRsrcLoader.java:58)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.hadoop.util.RunJar.run(RunJar.java:221)
at org.apache.hadoop.util.RunJar.main(RunJar.java:136)
Caused by: java.io.IOException: No FileSystem for scheme: hdfs
at org.apache.hadoop.fs.FileSystem.getFileSystemClass(FileSystem.java:2660)
at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:2667)
at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:94)
at org.apache.hadoop.fs.FileSystem$Cache.getInternal(FileSystem.java:2703)
at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:2685)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:373)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:172)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:357)
at org.apache.hadoop.fs.Path.getFileSystem(Path.java:295)
at org.apache.hadoop.mapreduce.lib.input.FileInputFormat.addInputPath(FileInputFormat.java:520)
at stringSearchJob.StringSearch.main(StringSearch.java:28)
... 11 more

Answer 1

将输入和输出目录设置为JobConf对象而不是Job对象

您必须进行以下更改：

 FileInputFormat.setInputPaths(conf /*from job to conf*/, new Path(args[0]));
 FileOutputFormat.setOutputPath(conf /*from job to conf*/, new Path(args[1]));

因此，修改后的代码应如下所示：

if (argv.length<3) {
                System.err.println("Give the input/ output/ keyword!");
                return;
            }
            JobConf conf = new JobConf(StringSearch.class);
            Job job = new Job(conf,"StringSearch");

            FileInputFormat.setInputPaths(conf, new Path(args[0]));
     FileOutputFormat.setOutputPath(conf, new Path(args[1]));
            conf.set("search", argv[2]);

            job.setJarByClass(StringSearch.class);
            job.setMapperClass(WordMapper.class);
            job.setNumReduceTasks(0);

            job.setMapOutputKeyClass(Text.class);
            job.setMapOutputValueClass(IntWritable.class);

            job.setOutputKeyClass(Text.class);
            job.setOutputValueClass(IntWritable.class);

            JobClient.runJob(conf); 
            job.waitForCompletion(true);