Mapreduce求TopK最大值

素颜马尾好姑娘i 2022-08-26 12:15 159阅读 0赞

package suanfa;
    
    
    import java.io.IOException;
    import java.net.URI;
    
    
    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.NullWritable;
    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.input.TextInputFormat;
    import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
    import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
    import org.apache.hadoop.mapreduce.lib.partition.HashPartitioner;
    
    
    public class TopK {
    
    public static final String INPUT_PATH="hdfs://192.168.0.9:9000/seq100w.txt";
    public static final String OUTPUT_PATH="hdfs://192.168.0.9:9000/maxseq";
    
    public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    Job job = new Job(conf,TopK.class.getSimpleName());
    
    //设置输入路径
    FileInputFormat.addInputPath(job, new Path(INPUT_PATH));
    //设置输入格式化
    job.setInputFormatClass(TextInputFormat.class);
    
    //设置自定义map
    job.setMapperClass(MyMapper.class);
    //设置map输出类型
    job.setMapOutputKeyClass(LongWritable.class);
    job.setMapOutputValueClass(NullWritable.class);
    
    //分区
    job.setPartitionerClass(HashPartitioner.class);
    //设置reduce任务
    job.setNumReduceTasks(1);
    
    //排序、分组
    
    //规约
    
    //设置自定义reduce类
    job.setReducerClass(MyReduce.class);
    //设置reduce输出类型
    job.setOutputKeyClass(LongWritable.class);
    job.setOutputValueClass(NullWritable.class);
    
    //删除已存在的路径
    FileSystem fileSystem = FileSystem.get(new URI(INPUT_PATH), conf);
    Path path=new Path(OUTPUT_PATH);
    if(fileSystem.exists(path)){
    fileSystem.delete(path,true);
    }
    
    //设置输出路径
    FileOutputFormat.setOutputPath(job, new Path(OUTPUT_PATH));
    //设置输出格式化类
    job.setOutputFormatClass(TextOutputFormat.class);
    
    //提交任务
    job.waitForCompletion(true);
    }
    
    static class MyMapper extends Mapper<LongWritable, Text, LongWritable, NullWritable>{
    public long max=Long.MIN_VALUE;
    @Override
    protected void map(LongWritable key, Text value,Context context)
    throws IOException, InterruptedException {
    long temp=Long.parseLong(value.toString());
    if(temp>max){
    max=temp;
    }
    }
    
    @Override
    protected void cleanup(Context context)
    throws IOException, InterruptedException {
    context.write(new LongWritable(max), NullWritable.get());
    }
    }
    
    static class MyReduce extends Reducer<LongWritable, NullWritable, LongWritable, NullWritable>{
    public long max=Long.MIN_VALUE;
    @Override
    protected void reduce(LongWritable k2, Iterable<NullWritable> v2s,Context context)
    throws IOException, InterruptedException {
    long temp=k2.get();
    if(temp>max){
    max=temp;
    }
    }
    
    @Override
    protected void cleanup(Context context)
    throws IOException, InterruptedException {
    context.write(new LongWritable(max), NullWritable.get());
    }
    }
    }