1.MapReduce计算框架

2.实例WordCount

package org.apache.hadoop.examples; 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; import org.apache.hadoop.mapred.TextInputFormat; import org.apache.hadoop.mapred.TextOutputFormat; import org.apache.hadoop.util.GenericOptionsParser; public class WordCount { // This is the Mapper class public static class TokenizerMapper extends Mapper<Object, Text, Text, IntWritable>{ //define IntWritaable class object one private final static IntWritable one = new IntWritable(1); private Text word = new Text(); public void map(Object key, Text value, Context context ) throws IOException, InterruptedException { StringTokenizer itr = new StringTokenizer(value.toString()); while (itr.hasMoreTokens()) { word.set(itr.nextToken()); context.write(word, one); } } } public static class IntSumCombiner 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); } } // This is the Reducer class // count of word = count set output format public static class IntSumReducer extends Reducer<Text,IntWritable,Text,Text> { private Text result_key= new Text(); private Text result_value= new Text(); private byte[] prefix; private byte[] suffix; protected void setup(Context context) { try { prefix= Text.encode("count of ").array(); suffix= Text.encode(" =").array(); } catch (Exception e) { prefix = suffix = new byte[0]; } } public void reduce(Text key, Iterable<IntWritable> values, Context context ) throws IOException, InterruptedException { int sum = 0; for (IntWritable val : values) { sum += val.get(); } // generate result key result_key.set(prefix); result_key.append(key.getBytes(), 0, key.getLength()); result_key.append(suffix, 0, suffix.length); // generate result value result_value.set(Integer.toString(sum)); context.write(result_key, result_value); } } public static void main(String[] args) throws Exception { Configuration conf = new Configuration(); System.out.println("conf information: "+conf.toString()); String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs(); System.out.println("otherArgs:"); for(int i=0;i<otherArgs.length;i++) System.out.println(otherArgs[i]); if (otherArgs.length < 2) { System.err.println("Usage: wordcount <in> [<in>...] <out>"); System.exit(2); } Job job = Job.getInstance(conf, "word count"); job.setJarByClass(WordCount.class); job.setMapperClass(TokenizerMapper.class); job.setCombinerClass(IntSumCombiner.class); job.setReducerClass(IntSumReducer.class); job.setMapOutputKeyClass(Text.class); job.setMapOutputValueClass(IntWritable.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(Text.class); // add the input paths as given by command line for (int i = 0; i < otherArgs.length - 1; ++i) { FileInputFormat.addInputPath(job, new Path(otherArgs[i])); System.out.println("=================================="); System.out.println(otherArgs[i]); } System.out.println(otherArgs[otherArgs.length - 1]); // add the output path as given by the command line FileOutputFormat.setOutputPath(job, new Path(otherArgs[otherArgs.length - 1])); System.exit(job.waitForCompletion(true) ? 0 : 1); } }