= 將 wordcount2 改成 0.20 版 =

 == 前言 ==
按照hadoop 0.20 官方網頁的 wordcount v2 .[[BR]]
[http://hadoop.apache.org/common/docs/r0.20.1/mapred_tutorial.html#Example%3A+WordCount+v1.0  WordCount]

最需要給的地方是 ''' " extends MapReduceBase implements Mapper" ''' 原因是在hadoop 0.20時，mapreducebase 此class已經被deprecated，[[BR]]
因此應改寫如 ''' " extends Mapper" '''

然而最主要不能改變的原因是，程式中很重要的功能 [http://hadoop.apache.org/common/docs/r0.20.1/api/org/apache/hadoop/filecache/DistributedCache.html DistributedCache ]  以及 -Dwordcount.skip.patterns 等功能寫於 configure() 函數內。 此configure() 繼承自 MapReduceBase，[[BR]]
因此若整個程式改成hadoop 0.20 的 " extends Mapper" '''，則有些功能將不知是否能使用


 == 原始程式碼 ==

{{{
#!java
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.filecache.DistributedCache;
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.FileInputFormat;
import org.apache.hadoop.mapred.FileOutputFormat;
import org.apache.hadoop.mapred.JobClient;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapred.Mapper;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reducer;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.mapred.TextInputFormat;
import org.apache.hadoop.mapred.TextOutputFormat;
import org.apache.hadoop.util.StringUtils;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;
public class WordCountV2 extends Configured implements Tool {

	public static class Map extends MapReduceBase implements
			Mapper<LongWritable, Text, Text, IntWritable> {

		static enum Counters {
			INPUT_WORDS
		}

		private final static IntWritable one = new IntWritable(1);
		private Text word = new Text();

		private boolean caseSensitive = true;
		private Set<String> patternsToSkip = new HashSet<String>();

		private long numRecords = 0;
		private String inputFile;

		public void configure(JobConf job) {
			caseSensitive = job.getBoolean("wordcount.case.sensitive", true);
			inputFile = job.get("map.input.file");

			if (job.getBoolean("wordcount.skip.patterns", false)) {
				Path[] patternsFiles = new Path[0];
				try {
					patternsFiles = DistributedCache.getLocalCacheFiles(job);
				} catch (IOException ioe) {
					System.err
							.println("Caught exception while getting cached files: "
									+ StringUtils.stringifyException(ioe));
				}
				for (Path patternsFile : patternsFiles) {
					parseSkipFile(patternsFile);
				}
			}
		}

		private void parseSkipFile(Path patternsFile) {
			try {
				BufferedReader fis = new BufferedReader(new FileReader(
						patternsFile.toString()));
				String pattern = null;
				while ((pattern = fis.readLine()) != null) {
					patternsToSkip.add(pattern);
				}
			} catch (IOException ioe) {
				System.err
						.println("Caught exception while parsing the cached file '"
								+ patternsFile
								+ "' : "
								+ StringUtils.stringifyException(ioe));
			}
		}

		public void map(LongWritable key, Text value,
				OutputCollector<Text, IntWritable> output, Reporter reporter)
				throws IOException {
			String line = (caseSensitive) ? value.toString() : value.toString()
					.toLowerCase();

			for (String pattern : patternsToSkip) {
				line = line.replaceAll(pattern, "");
			}

			StringTokenizer tokenizer = new StringTokenizer(line);
			while (tokenizer.hasMoreTokens()) {
				word.set(tokenizer.nextToken());
				output.collect(word, one);
				reporter.incrCounter(Counters.INPUT_WORDS, 1);
			}

			if ((++numRecords % 100) == 0) {
				reporter.setStatus("Finished processing " + numRecords
						+ " records " + "from the input file: " + inputFile);
			}
		}
	}

	public static class Reduce extends MapReduceBase implements
			Reducer<Text, IntWritable, Text, IntWritable> {
		public void reduce(Text key, Iterator<IntWritable> values,
				OutputCollector<Text, IntWritable> output, Reporter reporter)
				throws IOException {
			int sum = 0;
			while (values.hasNext()) {
				sum += values.next().get();
			}
			output.collect(key, new IntWritable(sum));
		}
	}

	public int run(String[] args) throws Exception {


		JobConf conf = new JobConf(getConf(), WordCount.class);
		conf.setJobName("wordcount");

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

		conf.setMapperClass(Map.class);
		conf.setCombinerClass(Reduce.class);
		conf.setReducerClass(Reduce.class);

		conf.setInputFormat(TextInputFormat.class);
		conf.setOutputFormat(TextOutputFormat.class);

		List<String> other_args = new ArrayList<String>();
		for (int i = 0; i < args.length; ++i) {
			if ("-skip".equals(args[i])) {
				DistributedCache
						.addCacheFile(new Path(args[++i]).toUri(), conf);
				conf.setBoolean("wordcount.skip.patterns", true);
			} else {
				other_args.add(args[i]);
			}
		}

		FileInputFormat.setInputPaths(conf, new Path(other_args.get(0)));
		FileOutputFormat.setOutputPath(conf, new Path(other_args.get(1)));
		CheckAndDelete.checkAndDelete(other_args.get(1), conf);
		JobClient.runJob(conf);
		return 0;
	}

	public static void main(String[] args) throws Exception {
		String[] argv = { "-Dwordcount.case.sensitive=false",
				"/user/waue/input", "/user/waue/output-wc2", "-skip",
				"/user/waue/patterns/patterns.txt" };
		args = argv;
		int res = ToolRunner.run(new Configuration(), new WordCountV2(), args);
		System.exit(res);
	}
}
}}}

 == 修改 ==

此程式碼用hadoop 0.20的api 將 deprecated 修正，然而卻出現以下錯誤

{{{
#!text
 Exception in thread "main" java.lang.NullPointerException
at WordCountV020.run(WordCountV020.java:127)
at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:65)
at WordCountV020.main(WordCountV020.java:147)
}}}

由於 ''' patternsFiles = DistributedCache.getLocalCacheFiles(conf); ''' 沒有取到任何資料，因此出錯



=== 修改後原始碼 ===

{{{
#!java
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.filecache.DistributedCache;
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.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.util.StringUtils;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

public class WordCountV020 extends Configured implements Tool {

	static boolean caseSensitive = true;
	static Set<String> patternsToSkip = new HashSet<String>();

	static void parseSkipFile(Path patternsFile) {
		try {
			BufferedReader fis = new BufferedReader(new FileReader(patternsFile
					.toString()));
			String pattern = null;
			while ((pattern = fis.readLine()) != null) {
				patternsToSkip.add(pattern);
			}
		} catch (IOException ioe) {
			System.err
					.println("Caught exception while parsing the cached file '"
							+ patternsFile + "' : "
							+ StringUtils.stringifyException(ioe));
		}
	}

	public static class Map extends
			Mapper<LongWritable, Text, Text, IntWritable> {

		static enum Counters {
			INPUT_WORDS
		}

		private final static IntWritable one = new IntWritable(1);
		private Text word = new Text();

		public void map(LongWritable key, Text value, Context context)
				throws IOException, InterruptedException {

			String line = (caseSensitive) ? value.toString() : value.toString()
					.toLowerCase();

			for (String pattern : patternsToSkip) {
				line = line.replaceAll(pattern, "");
			}

			StringTokenizer tokenizer = new StringTokenizer(line);
			while (tokenizer.hasMoreTokens()) {
				word.set(tokenizer.nextToken());
				context.write(word, one);

			}

		}
	}

	public static class Reduce extends
			Reducer<Text, IntWritable, Text, IntWritable> {
		public void reduce(Text key, Iterator<IntWritable> values, Context context)
				throws IOException, InterruptedException {
			int sum = 0;
			while (values.hasNext()) {
				sum += values.next().get();
			}
			context.write(key, new IntWritable(sum));
		}
	}

	public int run(String[] args) throws Exception {

		Configuration conf = new Configuration();
		// 宣告job 取得conf 並設定名稱 Hadoop Hello World
		Job job = new Job(conf, "Hadoop Hello World");
		// 設定此運算的主程式
		job.setJarByClass(HelloHadoop.class);

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

		job.setMapperClass(Map.class);
		job.setCombinerClass(Reduce.class);
		job.setReducerClass(Reduce.class);

		List<String> other_args = new ArrayList<String>();
		for (int i = 0; i < args.length; ++i) {
			if ("-skip".equals(args[i])) {
				DistributedCache
						.addCacheFile(new Path(args[++i]).toUri(), conf);
				conf.setBoolean("wordcount.skip.patterns", true);
			} else {
				other_args.add(args[i]);
			}
		}

		caseSensitive = conf.getBoolean("wordcount.case.sensitive", true);

		if (conf.getBoolean("wordcount.skip.patterns", false)) {
			Path[] patternsFiles = new Path[0];
			try {
				patternsFiles = DistributedCache.getLocalCacheFiles(conf);
				
			} catch (IOException ioe) {
				System.err
						.println("Caught exception while getting cached files: "
								+ StringUtils.stringifyException(ioe));
			}
			for (Path patternsFile : patternsFiles) {
				parseSkipFile(patternsFile);
			}
		}

		FileInputFormat.setInputPaths(job, new Path(other_args.get(0)));
		// 設定輸出路徑
		FileOutputFormat.setOutputPath(job, new Path(other_args.get(1)));

		CheckAndDelete.checkAndDelete(other_args.get(1), conf);
		job.waitForCompletion(true);
		return 0;
	}

	public static void main(String[] args) throws Exception {
		String[] argv = { "-Dwordcount.case.sensitive=false",
				"/user/waue/input", "/user/waue/output-v020", "-skip",
				"/user/waue/patterns/patterns.txt" };
		args = argv;
		int res = ToolRunner
				.run(new Configuration(), new WordCountV020(), args);
		System.exit(res);
	}
}
}}}