Java Hadoop错误。ClassCastException:org.apache.Hadoop.io.LongWritable无法强制转换为org.apache.Hadoop.io.Text
我的计划如下:Java Hadoop错误。ClassCastException:org.apache.Hadoop.io.LongWritable无法强制转换为org.apache.Hadoop.io.Text,java,hadoop,mapreduce,Java,Hadoop,Mapreduce,我的计划如下: public static class MapClass extends Mapper<Text, Text, Text, LongWritable> { public void map(Text key, Text value, Context context) throws IOException, InterruptedException { // your map code goes here
public static class MapClass extends Mapper<Text, Text, Text, LongWritable> {
public void map(Text key, Text value, Context context) throws IOException, InterruptedException {
// your map code goes here
String[] fields = value.toString().split(",");
for(String str : fields) {
context.write(new Text(str), new LongWritable(1L));
}
}
}
public int run(String args[]) throws Exception {
Job job = new Job();
job.setJarByClass(TopOS.class);
job.setMapperClass(MapClass.class);
FileInputFormat.setInputPaths(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
job.setJobName("TopOS");
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(LongWritable.class);
job.setNumReduceTasks(0);
boolean success = job.waitForCompletion(true);
return success ? 0 : 1;
}
public static void main(String args[]) throws Exception {
int ret = ToolRunner.run(new TopOS(), args);
System.exit(ret);
}
}
为什么会出现以下错误?我怎样才能避开这件事
Hadoop : java.lang.ClassCastException: org.apache.hadoop.io.LongWritable cannot be cast to org.apache.hadoop.io.Text
你能用吗
//Set the key class for the job output data.
job.setOutputKeyClass(Class<?> theClass)
//Set the value class for job outputs
job.setOutputValueClass(Class<?> theClass)
//设置作业输出数据的键类。
job.setOutputKeyClass(类的类)
//设置作业输出的值类
job.setOutputValueClass(类的类)
而不是setMapOutputKeyClass和setMapOutputValueClass方法。在我看来,代码中只有一个小错误 当您使用平面文本文件作为输入时,fixed key类是LongWritable(您不需要/使用的),value类是ist Text 将映射器中的keyClass设置为Object,以便在不使用它的情况下加下划线,就可以消除错误 这是我稍微修改过的代码
package org.woopi.stackoverflow.q22853574;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.lib.input.*;
import org.apache.hadoop.mapreduce.lib.output.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.fs.Path;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
public class MapReduceJob {
public static class MapClass extends Mapper<Object, Text, Text, LongWritable> {
public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
// your map code goes here
String[] fields = value.toString().split(",");
for(String str : fields) {
context.write(new Text(str), new LongWritable(1L));
}
}
}
public int run(String args[]) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf);
job.setJarByClass(MapReduceJob.class);
job.setMapperClass(MapClass.class);
FileInputFormat.setInputPaths(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
job.setJobName("MapReduceJob");
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(LongWritable.class);
job.setNumReduceTasks(0);
job.setInputFormatClass(TextInputFormat.class);
boolean success = job.waitForCompletion(true);
return success ? 0 : 1;
}
public static void main(String args[]) throws Exception {
MapReduceJob j = new MapReduceJob();
int ret = j.run(args);
System.exit(ret);
}
package org.woopi.stackoverflow.q22853574;
导入org.apache.hadoop.io.*;
导入org.apache.hadoop.mapreduce.lib.input.*;
导入org.apache.hadoop.mapreduce.lib.output.*;
导入org.apache.hadoop.mapreduce.*;
导入org.apache.hadoop.fs.Path;
导入java.io.IOException;
导入org.apache.hadoop.conf.Configuration;
公共类MapReduceJob{
公共静态类映射器类扩展映射器{
公共void映射(对象键、文本值、上下文上下文)引发IOException、InterruptedException{
//你的地图代码在这里
字符串[]字段=value.toString().split(“,”);
for(字符串str:fields){
编写(新文本(str)、新长可写(1L));
}
}
}
公共int运行(字符串args[])引发异常{
Configuration conf=新配置();
Job Job=Job.getInstance(conf);
job.setJarByClass(MapReduceJob.class);
job.setMapperClass(MapClass.class);
setInputPaths(作业,新路径(args[0]);
setOutputPath(作业,新路径(args[1]);
job.setJobName(“MapReduceJob”);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(LongWritable.class);
job.setNumReduceTasks(0);
setInputFormatClass(TextInputFormat.class);
布尔值success=job.waitForCompletion(true);
返回成功?0:1;
}
公共静态void main(字符串args[])引发异常{
MapReduceJob j=新的MapReduceJob();
int-ret=j.run(args);
系统退出(ret);
}
我希望这有帮助
Martin我看不出哪里违反了继承树。输出键是文本,而LongWritable是输出值。你能解释一下吗?我不明白你的意思。
Mapper
应该改为Mapper
。键是当前行的文件偏移量。它的类型是LongWritable。
package org.woopi.stackoverflow.q22853574;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.lib.input.*;
import org.apache.hadoop.mapreduce.lib.output.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.fs.Path;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
public class MapReduceJob {
public static class MapClass extends Mapper<Object, Text, Text, LongWritable> {
public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
// your map code goes here
String[] fields = value.toString().split(",");
for(String str : fields) {
context.write(new Text(str), new LongWritable(1L));
}
}
}
public int run(String args[]) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf);
job.setJarByClass(MapReduceJob.class);
job.setMapperClass(MapClass.class);
FileInputFormat.setInputPaths(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
job.setJobName("MapReduceJob");
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(LongWritable.class);
job.setNumReduceTasks(0);
job.setInputFormatClass(TextInputFormat.class);
boolean success = job.waitForCompletion(true);
return success ? 0 : 1;
}
public static void main(String args[]) throws Exception {
MapReduceJob j = new MapReduceJob();
int ret = j.run(args);
System.exit(ret);
}