浅谈MapReduce

最新推荐文章于 2022-04-26 16:43:41 发布

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最新推荐文章于 2022-04-26 16:43:41 发布

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最近研究hadoop mapreduce，总结一下研究的结果。

eclipse中写一个简单的mapreduce程序：

1.首先配置eclipse 与 hadoop，其配置方式如下：

http://www.cnblogs.com/kinglau/p/3802705.html

配置完后就可以开始创建mapreduce程序了。

2.创建MapReduce Project工程。并准备输入文件。

输入文件：

file1： hello word file2： hello

hadoop word good

welcome good

3.创建Mapper Class，继承Mapper<Object, Text, Text, IntWritable>,并重写map(Object key, Text value, Context context)方法。

public class HadoopMapper extends Mapper<Object, Text, Text, IntWritable> {
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);
}
}
}

4.创建Reduce Class，继承Reducer<Text,IntWritable,Text,IntWritable>，并重写reduce(Text key, Iterable<IntWritable> values, Context context)方法。

public class HadoopReducer 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);
}
}

5.创建MapReduce Drver Class。

public class HadoopMain {
@SuppressWarnings("deprecation")
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
String[] otherArgs=new GenericOptionsParser(conf,args).getRemainingArgs();
for(String s: otherArgs){
System.out.println(s);
}
if (otherArgs.length != 2){
System.out.println("Usage:wordcount <in> <out>");
System.exit(2);
}
Job job=new Job(conf,"MaxPara1");
job.setJarByClass(HadoopMatlabMain.class);
job.setMapperClass(HadoopMatlabMapper.class);
job.setCombinerClass(HadoopMatlabReducer.class);
job.setReducerClass(HadoopMatlabReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
System.exit(job.waitForCompletion(true) ? 0:1);
}
}