MapReduce TopK统计加排序中介绍的TopK在mapreduce的实现。

本案例省略的上面案例中的Sort步骤，改用TreeMap来实现获取前K个词

package TopK1;
import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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;

/**
 * 统计词频
 * @author zx
 * zhangxian1991@qq.com
 */
public class WordCount {
	
	/**
	 * 读取单词
	 * @author zx
	 *
	 */
	public static class Map extends Mapper<Object,Text,Text,IntWritable>{

		IntWritable count = new IntWritable(1);
		
		@Override
		protected void map(Object key, Text value, Context context)
				throws IOException, InterruptedException {
			StringTokenizer st = new StringTokenizer(value.toString());
			while(st.hasMoreTokens()){	
				String word = st.nextToken().replaceAll("\"", "").replace("'", "").replace(".", "");
				context.write(new Text(word), count);
			}
		}
		
	}
	
	/**
	 * 统计词频
	 * @author zx
	 *
	 */
	public static class Reduce extends Reducer<Text,IntWritable,Text,IntWritable>{

		@SuppressWarnings("unused")
		@Override
		protected void reduce(Text key, Iterable<IntWritable> values,Context context)
				throws IOException, InterruptedException {
			int count = 0;
			for (IntWritable intWritable : values) {
				count ++;
			}
			context.write(key,new IntWritable(count));
		}
		
	}
	
	@SuppressWarnings("deprecation")
	public static boolean run(String in,String out) throws IOException, ClassNotFoundException, InterruptedException{
		
		FileUtil.deleteFile(out);

		Configuration conf = new Configuration();
		
		Job job = new Job(conf,"WordCount1");
		job.setJarByClass(WordCount.class);
		job.setMapperClass(Map.class);
		job.setReducerClass(Reduce.class);
		
		// 设置Map输出类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);

        // 设置Reduce输出类型
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

        // 设置输入和输出目录
        FileInputFormat.addInputPath(job, new Path(in));
        FileOutputFormat.setOutputPath(job, new Path(out));
        
        return job.waitForCompletion(true);
	}
	
}

package TopK1;

import java.io.IOException;
import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeMap;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
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.NullOutputFormat;

/**
 * 
 * @author zx
 *zhangxian1991@qq.com
 */
public class TopK {

	public static class TopKMap extends Mapper<Object, Text, IntWritable, IntWritable>{

		TreeMap<Integer,String> tm = new TreeMap<Integer,String>(new Comparator<Integer>() {

			/**
			 * treeMap中的元素逆序排列
			 * @param o1
			 * @param o2
			 * @return
			 */
			@Override
			public int compare(Integer o1, Integer o2) {
				return o2.compareTo(o1);
			}
			
		});
		int k = 0;
		
		@Override
		protected void cleanup(Context context) throws IOException,
				InterruptedException {
			Configuration conf = context.getConfiguration();
			Path topKPath = new Path(conf.get("topKOut"));
			FileSystem fs = topKPath.getFileSystem(conf);
			FSDataOutputStream fsDOS = fs.create(topKPath);
			Iterator<Integer> it = tm.keySet().iterator();
			while(it.hasNext()){
				Integer key = it.next();
				String value = http://www.mamicode.com/tm.get(key).toString();>
package TopK1;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

/**
 * 
 * @author zx
 *
 */
public class FileUtil {

	/**
	 * 上传数据文件到hdfs
	 * @param inputPath
	 * @param fileName
	 * @return
	 * @throws IOException
	 */
	public static String loadFile(String inputPath,String folder,String fileName) throws IOException{
		
		//获取数据文件的全路径
		
		
		if(null != folder && !"".equals(folder)){
			folder = folder + "/";
		}
		
		String srcPathDir = FileUtil.class.getProtectionDomain().getCodeSource().getLocation()
                .getFile() + folder + fileName;
		
		Path srcpath = new Path("file:///" + srcPathDir);
		
		Path dstPath = new Path(getJobRootPath(inputPath) + fileName);
		
		Configuration conf = new Configuration();
		
		FileSystem fs = dstPath.getFileSystem(conf);
		
		fs.delete(dstPath, true);
		
		fs.copyFromLocalFile(srcpath, dstPath);
		
		fs.close();
		
		return getJobRootPath(inputPath) + fileName;
	}
	
	/**
	 * 如果路径的最后不包哈“/”就加一个“/”
	 * @param path
	 * @return
	 */
	public static String getJobRootPath(String path){
		if(path.lastIndexOf("/") == path.length()-1){
			path = path.substring(0, path.lastIndexOf("/"));
		}
		return path.substring(0, path.lastIndexOf("/")+1);
	}
	
	public static void deleteFile(String ...filePath) throws IOException{
		Configuration conf = new Configuration();
		for (int i = 0; i < filePath.length; i++) {
			Path path = new Path(filePath[i]);
			FileSystem fs = path.getFileSystem(conf);
			fs.delete(path,true);
		}
	}
	
}