我正在尝试编写简单的map reduce程序,以使用新的API(0.20.2)找到最大的素数 . 这就是我的Map和reduce类的样子......
public class PrimeNumberMap extends Mapper<LongWritable, Text, IntWritable, IntWritable> {
public void map (LongWritable key, Text Kvalue,Context context) throws IOException,InterruptedException
{
Integer value = new Integer(Kvalue.toString());
if(isNumberPrime(value))
{
context.write(new IntWritable(value), new IntWritable(new Integer(key.toString())));
}
}
boolean isNumberPrime(Integer number)
{
if (number == 1) return false;
if (number == 2) return true;
for (int counter =2; counter<(number/2);counter++)
{
if(number%counter ==0 )
return false;
}
return true;
}
}
public class PrimeNumberReduce extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> {
public void reduce ( IntWritable primeNo, Iterable<IntWritable> Values,Context context) throws IOException ,InterruptedException
{
int maxValue = Integer.MIN_VALUE;
for (IntWritable value : Values)
{
maxValue= Math.max(maxValue, value.get());
}
//output.collect(primeNo, new IntWritable(maxValue));
context.write(primeNo, new IntWritable(maxValue)); }
}
public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException{
if (args.length ==0)
{
System.err.println(" Usage:\n\tPrimenumber <input Directory> <output Directory>");
System.exit(-1);
}
Job job = new Job();
job.setJarByClass(Main.class);
job.setJobName("Prime");
// Creating job configuration object
FileInputFormat.addInputPath(job, new Path (args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
job.setMapOutputKeyClass(IntWritable.class);
job.setMapOutputValueClass(IntWritable.class);
job.setOutputKeyClass(IntWritable.class);
job.setOutputValueClass(IntWritable.class);
String star ="*********************************************";
System.out.println(star+"\n Prime number computer \n"+star);
System.out.println(" Application started ... keeping fingers crossed :/ ");
System.exit(job.waitForCompletion(true)?0:1);
}
}
我仍然收到关于 Map 密钥不匹配的错误
java.io.IOException:键入map中的键不匹配:期望org.apache.hadoop.io.IntWritable,收到org.apache.hadoop.mapred.MapTask上的org.apache.hadoop.io.LongWritable $ MapOutputBuffer.collect(位于org.apache的org.apache.hadoop.mapred.MapTask $ NewOutputCollector.write(MapTask.java:595)org.apache的org.apache.hadoop.mapreduce.TaskInputOutputContext.write(TaskInputOutputContext.java:80)中的MapTask.java:1034)位于org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java)org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)的.hadoop.mapreduce.Mapper.map(Mapper.java:124) :668)atg.apache.hadoop.mapred.MapTask.run(MapTask.java:334)atg.apache.hadoop.mapred.Child $ 4.run(Child.java:270)at java.security.AccessController.doPrivileged (本机方法)位于org.apache.hadoop.mapred.Child的org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1109)的javax.security.auth.Subject.doAs(Subject.java:396) .main(Child.java:264)2012-06-13 14:27:21,116 INFO org.apache.hadoop.mapre d.Task:为任务运行清理
有人可以建议有什么不对 . 我试过所有的钩子和骗子 .
3 回答
您没有在主块中配置Mapper或reducer类,因此正在使用默认的Mapper(称为标识映射器) - 它输出的每一对都是输出(因此LongWritable作为输出键):
代替
请参阅Hadoop权威指南第3版,第2章,第24页
我是hadoop mapreduce程序的新手 .
映射时,我使用
IntWritable
但是我减少了IntWritable
格式的值,并在上下文写入中使用DoubleWritable
之前将结果转换为double .运行时失败 .
我在map中处理covert int的方法是double in double: