我希望通过hadoop map reduce应用程序从顺序文件中获取所有键值对。 我跟着帖子http://lintool.github.com/Cloud9/docs/content/staging-records.html来阅读主要课程中的顺序文件但该工作正常。 我想将所有keysvalue对打印到hdfs系统中的普通文本文件,我该如何实现呢? 我写下了我的代码。
import java.io.File;
import java.io.IOException;
import java.util.*;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FileUtil;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.SequenceFileAsBinaryInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
public class WordCount
{
public static class Map extends Mapper
{
private final static IntWritable one = new IntWritable(1);
private Text word = new Text();
public void map(BytesWritable key, BytesWritable value, Context context) throws IOException, InterruptedException
{
System.out.println(key.toString());
System.out.println(value.toString());
context.write(key, value);
}
}
public static class Reduce extends Reducer
{
public void reduce(Text key, Iterable<IntWritable> values, Context context)
throws IOException, InterruptedException
{
int sum = 0;
for (IntWritable val : values)
{
sum += val.get();
}
context.write(key, new IntWritable(sum));
}
}
public static void main(String[] args) throws Exception
{
FileUtil.fullyDelete(new File(args[1]));
Configuration conf = new Configuration();
Job job = new Job(conf, "wordcount");
job.setOutputKeyClass(BytesWritable.class);
job.setOutputValueClass(BytesWritable.class);
job.setMapperClass(Map.class);
job.setReducerClass(Reduce.class);
job.setInputFormatClass(org.apache.hadoop.mapreduce.lib.input.SequenceFileAsBinaryInputFormat.class);
job.setOutputFormatClass(TextOutputFormat.class);
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
job.setJarByClass(WordCount.class);
job.waitForCompletion(true);
}
}
答案 0 :(得分:1)
使用以下代码读取所有键/值对。根据需要更改它。
public class SequenceFileReader {
public static void main(String args[]) throws Exception {
System.out.println("Readeing Sequence File");
Configuration conf = new Configuration();
conf.addResource(new Path("/home/mohammad/hadoop-0.20.203.0/conf/core-site.xml"));
conf.addResource(new Path("/home/mohammad/hadoop-0.20.203.0/conf/hdfs-site.xml"));
FileSystem fs = FileSystem.get(conf);
Path path = new Path("/seq/file");
SequenceFile.Reader reader = null;
try {
reader = new SequenceFile.Reader(fs, path, conf);
Writable key = (Writable) ReflectionUtils.newInstance(reader.getKeyClass(), conf);
Writable value = (Writable) ReflectionUtils.newInstance(reader.getValueClass(), conf);
while (reader.next(key, value)) {
System.out.println(key + " <===> " + value.toString());
}
} catch (Exception e) {
e.printStackTrace();
} finally {
IOUtils.closeStream(reader);
}
}
}
答案 1 :(得分:1)
Please find the Below program. It may be useful in getting some idea in converting BytesWritable to Text.
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.WritableUtils;
import org.apache.hadoop.io.SequenceFile.Reader;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.util.ReflectionUtils;
public class SequenceFileRead {
public static void main(String args[]) throws IOException{
Configuration conf=new Configuration();
Path path=new Path(args[0]);
SequenceFile.Reader reader=null;
try{
reader=new SequenceFile.Reader(conf, Reader.file(path));
Text key= new Text();
BytesWritable value=new BytesWritable();
while(reader.next(key,value)){
System.out.println(key);
byte[] bytes=value.getBytes();
int size=bytes.length;
byte[] b=new byte[size];
InputStream is=new ByteArrayInputStream(bytes);
is.read(b);
System.out.println(new String(b));
}
}
finally {
IOUtils.closeStream(reader);
}
}
}