Hadoop WordCount 案例

  package com.syh;    import org.apache.hadoop.conf.Configuration;  import org.apache.hadoop.fs.FileSystem;  import org.apache.hadoop.fs.Path;  import org.apache.hadoop.io.LongWritable;  import org.apache.hadoop.io.Text;  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 java.io.IOException;    /**   * 词频统计   */  public class WordCountApp {      /**       * map 阶段       */      public static class MyMapper extends Mapper<LongWritable, Text, Text, LongWritable> {          LongWritable one = new LongWritable(1);            @Override          protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {              // 分              String line = value.toString();              // 拆分              String[] s = line.split(" ");              for (String word : s) {                  // 输出                  context.write(new Text(word), one);              }          }      }        /**       * reduce 阶段       */      public static class MyReducer extends Reducer<Text, LongWritable, Text, LongWritable> {          @Override          protected void reduce(Text key, Iterable<LongWritable> values, Context context) throws IOException, InterruptedException {              long sum = 0;              // 合并统计              for (LongWritable value : values) {                  // 求和                  sum += value.get();              }              context.write(key, new LongWritable(sum));          }      }        public static void main(String[] args) throws Exception {          Configuration configuration = new Configuration();          Job job = Job.getInstance(configuration, "wordcount");          job.setJarByClass(WordCountApp.class);            // 设置 map 相关参数          FileInputFormat.setInputPaths(job, new Path(args[0]));          job.setMapperClass(MyMapper.class);          job.setMapOutputKeyClass(Text.class);          job.setMapOutputValueClass(LongWritable.class);            // 设置 reduce 相关参数          job.setReducerClass(MyReducer.class);          job.setOutputKeyClass(MyReducer.class);          job.setOutputValueClass(LongWritable.class);            Path outPath = new Path(args[1]);          FileSystem fileSystem = FileSystem.get(configuration);          if (fileSystem.exists(outPath)) {              // 删除文件              fileSystem.delete(outPath, true);              System.out.println("输出路径已存在, 已被删除");          }          FileOutputFormat.setOutputPath(job, outPath);            // 控制台输出详细信息          // 输出：1  不输出：0          System.exit(job.waitForCompletion(true) ? 0 : 1);      }  }

  hadoop fs -rm -r /output/wc

  语法：  hadoop jar 主函数全限定名 输入 输出  示例：  hadoop jar hadoopdemo-1.0-SNAPSHOT.jar com.syh.WordCountApp hdfs://hadoop000:8020/WordCount.txt hdfs://hadoop000:8020/output/wc

  hadoop fs -cat /output/wc/part-r-00000