Java tutorial
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You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ //package org.apache.hadoop.examples; import java.io.IOException; import java.util.HashMap; import java.util.Iterator; import java.util.StringTokenizer; import java.util.Map.Entry; 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.Partitioner; 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.GenericOptionsParser; public class WordCountD { public static class TokenizerMapper extends Mapper<Object, Text, Text, IntWritable> { private final static IntWritable one = new IntWritable(1); private static HashMap<Text, IntWritable> RealWordMap; // Override the setup function to initialize the HashMap data structure @Override protected void setup(Context context) throws IOException, InterruptedException { super.setup(context); //Initializing the HashMap RealWordMap RealWordMap = new HashMap<Text, IntWritable>(); } public void map(Object key, Text value, Context context) throws IOException, InterruptedException { StringTokenizer itr = new StringTokenizer(value.toString()); while (itr.hasMoreTokens()) { String cur = itr.nextToken(); // Only count the real words starting with letters "m n o p q" // (no matter capitalized) if ((cur.charAt(0) >= 'm' && cur.charAt(0) <= 'q') || (cur.charAt(0) >= 'M' && cur.charAt(0) <= 'Q')) { // word.set(cur); Text word = new Text(cur); if (!RealWordMap.containsKey(word)) { // If the word never counted in HashMap, put it into HashMap RealWordMap.put(word, one); } else { // If the word already existing in HashMAP, change the value to plus one. IntWritable num = new IntWritable(RealWordMap.get(word).get() + 1); RealWordMap.put(word, num); } } } } // Override the cleanup function to clean the HashMap after all Map calls @Override protected void cleanup(Context context) throws IOException, InterruptedException { super.cleanup(context); //Emit the key from HashMap Iterator<Entry<Text, IntWritable>> iterator = RealWordMap.entrySet().iterator(); while (iterator.hasNext()) { Text keyText = iterator.next().getKey(); context.write(keyText, RealWordMap.get(keyText)); } } } /** * * @author junrongyan Partitioner class * */ public static class Letterpartitioner extends Partitioner<Text, IntWritable> { @Override public int getPartition(Text key, IntWritable value, int numReduceTasks) { String w = key.toString(); Character w1 = Character.toLowerCase(w.charAt(0)); //this is done to avoid performing mod with 0 if (numReduceTasks == 0) { return 0; } // Words starting with "M" or "m" assigned to reduce task 0 if (w1 == 'm') { return 0; } // Words starting with "N" or "n" assigned to reduce task 1 if (w1 == 'n') { return 1 % numReduceTasks; } // Words starting with "O" or "o" assigned to reduce task 2 if (w1 == 'o') { return 2 % numReduceTasks; } // Words starting with "P" or "p" assigned to reduce task 3 // Else, words starting with "Q" or "q" assigned to reduce task 4 if (w1 == 'p') { return 3 % numReduceTasks; } else { return 4 % numReduceTasks; } } } public static class IntSumReducer extends Reducer<Text, IntWritable, Text, IntWritable> { private IntWritable result = new IntWritable(); public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { int sum = 0; for (IntWritable val : values) { sum += val.get(); } result.set(sum); context.write(key, result); } } public static void main(String[] args) throws Exception { Configuration conf = new Configuration(); String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs(); if (otherArgs.length < 2) { System.err.println("Usage: wordcount <in> [<in>...] <out>"); System.exit(2); } Job job = Job.getInstance(conf, "word count"); job.setJarByClass(WordCountC.class); job.setMapperClass(TokenizerMapper.class); // Disable the combiner // job.setCombinerClass(IntSumReducer.class); // Setup the Partitioner job.setPartitionerClass(Letterpartitioner.class); job.setReducerClass(IntSumReducer.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); for (int i = 0; i < otherArgs.length - 1; ++i) { FileInputFormat.addInputPath(job, new Path(otherArgs[i])); } FileOutputFormat.setOutputPath(job, new Path(otherArgs[otherArgs.length - 1])); System.exit(job.waitForCompletion(true) ? 0 : 1); } }