我正在研究hadoop 1.2.1的字数示例。但是必须有所改变，因为我似乎无法使其正常工作。
这是我的Reduce类(class):
public static class Reduce extends Reducer<WritableComparable, Writable, WritableComparable, Writable> {
public void reduce(WritableComparable key,
Iterator<Writable> values,
OutputCollector<WritableComparable, NullWritable> output,
Reporter reporter) throws IOException {
output.collect(key, NullWritable.get());
}
}
而我的主要功能是:
public static void main(String[] args) throws Exception {
JobConf jobConf = new JobConf(MapDemo.class);
jobConf.setNumMapTasks(10);
jobConf.setNumReduceTasks(1);
jobConf.setJobName("MapDemo");
jobConf.setOutputKeyClass(Text.class);
jobConf.setOutputValueClass(NullWritable.class);
jobConf.setMapperClass(Map.class);
jobConf.setReducerClass(Reduce.class);
jobConf.setInputFormat(TextInputFormat.class);
jobConf.setOutputFormat(TextOutputFormat.class);
FileInputFormat.setInputPaths(jobConf, new Path(args[0]));
FileOutputFormat.setOutputPath(jobConf, new Path(args[1]));
JobClient.runJob(jobConf);
}
我的IDE告诉我有一个错误，由Maven证实:
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] com/example/mapreduce/MapDemo.java:[71,16] method setReducerClass in class org.apache.hadoop.mapred.JobConf cannot be applied to given types;
required: java.lang.Class<? extends org.apache.hadoop.mapred.Reducer>
found: java.lang.Class<com.example.mapreduce.MapDemo.Reduce>
reason: actual argument java.lang.Class<com.example.mapreduce.MapDemo.Reduce> cannot be converted to java.lang.Class<? extends org.apache.hadoop.mapred.Reducer> by method invocation conversion
[INFO] 1 error
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.679s
[INFO] Finished at: Mon Sep 16 09:23:08 PDT 2013
[INFO] Final Memory: 17M/202M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.0:compile (default-compile) on project inventory: Compilation failure
[ERROR] com/example/mapreduce/MapDemo.java:[71,16] method setReducerClass in class org.apache.hadoop.mapred.JobConf cannot be applied to given types;
[ERROR] required: java.lang.Class<? extends org.apache.hadoop.mapred.Reducer>
[ERROR] found: java.lang.Class<com.example.mapreduce.MapDemo.Reduce>
我相信网上的字数示例已过时1.2.1。我该如何解决？是否有人链接到有效的1.2.1字数统计Java源代码？
最佳答案
您跟随哪个链接？我从未见过这种WC。但是，无论您遵循什么，都肯定已经过时了，因为它正在使用旧的API。我怀疑您是否遵循正确。
这应该工作:
public class WordCount {
/**
* The map class of WordCount.
*/
public static class TokenCounterMapper 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);
}
}
}
/**
* The reducer class of WordCount
*/
public static class TokenCounterReducer extends
Reducer<Text, IntWritable, Text, IntWritable> {
public void reduce(Text key, Iterable<IntWritable> values,
Context context) throws IOException, InterruptedException {
int sum = 0;
for (IntWritable value : values) {
sum += value.get();
}
context.write(key, new IntWritable(sum));
}
}
/**
* The main entry point.
*/
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
conf.addResource(new Path("/Users/miqbal1/hadoop-eco/hadoop-1.1.2/conf/core-site.xml"));
conf.addResource(new Path("/Users/miqbal1/hadoop-eco/hadoop-1.1.2/conf/hdfs-site.xml"));
conf.set("fs.default.name", "hdfs://localhost:9000");
conf.set("mapred.job.tracker", "localhost:9001");
Job job = new Job(conf, "WordCount");
job.setJarByClass(WordCount.class);
job.setMapperClass(TokenCounterMapper.class);
job.setReducerClass(TokenCounterReducer.class);
job.setNumReduceTasks(2);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path("/inputs/demo.txt"));
FileOutputFormat.setOutputPath(job, new Path("/outputs/1111223"));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}
很少有观察可做: