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SequenceReader.java
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SequenceReader.java
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package com.continuumio.seqreaderapp;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.util.ReflectionUtils;
import org.apache.nutch.util.NutchConfiguration;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
public class SequenceReader {
private static final Configuration conf = NutchConfiguration.create();
private static final FileSystem fs;
static {
try {
fs = FileSystem.get(conf);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
//convert Java Types to Hadoop Writable Types
public static Object type_to_writable(Object obj) {
Object new_obj;
System.out.println(obj.toString());
System.out.println(obj == String.class);
if (obj.equals(String.class)){
new_obj = new Text();
}
else if (obj.equals(Integer.class)) {
new_obj = new IntWritable();
}
else {
new_obj = new Object();
}
return new_obj;
}
public static List head(int nrows, String path) throws IOException {
// read first nrows from sequence file
List<List> rows = new ArrayList<List>();
Path file = new Path(path);
System.out.println(file);
SequenceFile.Reader reader = new SequenceFile.Reader(conf, SequenceFile.Reader.file(file));
Writable key = (Writable)
ReflectionUtils.newInstance(reader.getKeyClass(), conf);
Writable value = (Writable)
ReflectionUtils.newInstance(reader.getValueClass(), conf);
int i = 0;
while(reader.next(key, value)) {
if (i == nrows) {
break;
}
try {
//hack JAVA tuple construction
//need to keep types simple for python conversion
List<String> t_row =new ArrayList<String>();
t_row.add(key.toString());
t_row.add(value.toString());
rows.add(t_row);
} catch (Exception e) {
//figure out something to do
// how to pass messags back upstream to python
}
i += 1;
}
return rows;
}
public static List read(String path) throws IOException {
// reads the entire contents of the file
List<List> rows=new ArrayList<List>();
Path file = new Path(path);
System.out.println(file);
SequenceFile.Reader reader = new SequenceFile.Reader(conf, SequenceFile.Reader.file(file));
Writable key = (Writable)
ReflectionUtils.newInstance(reader.getKeyClass(), conf);
Writable value = (Writable)
ReflectionUtils.newInstance(reader.getValueClass(), conf);
while(reader.next(key, value)) {
try {
//hack JAVA tuple construction
//need to keep types simple for python conversion
List<String> t_row =new ArrayList<String>();
t_row.add(key.toString());
t_row.add(value.toString());
rows.add(t_row);
}
catch (Exception e) {
}
}
return rows;
}
public static List slice(long start, long stop, String path) throws IOException {
//read rows between start and stop
List<List> rows=new ArrayList<List>();
Path file = new Path(path);
System.out.println(file);
SequenceFile.Reader reader = new SequenceFile.Reader(conf, SequenceFile.Reader.file(file));
Writable key = (Writable)
ReflectionUtils.newInstance(reader.getKeyClass(), conf);
Writable value = (Writable)
ReflectionUtils.newInstance(reader.getValueClass(), conf);
//skip rows
long i = 0;
for (; i < start && reader.next(key, value); i++ ); //Skip
for (; i < stop && reader.next(key, value); i++ ){
try {
//hack JAVA tuple construction
//need to keep types simple for python conversion
List<String> t_row =new ArrayList<String>();
t_row.add(key.toString());
t_row.add(value.toString());
rows.add(t_row);
}
catch (Exception e) {
e.printStackTrace();
}
}
return rows;
}
/**
* Lazily reads the sequence file as and when the records are consumed from
* the returned iterator
* @param path path of sequence file
* @param start starting record number
* @return Iterator of Writable list which stores key and value in first two indices
* @throws IOException when an error occurs
*/
public static RecordIterator getRecordIterator(String path, long start)
throws IOException {
return getRecordIterator(path, start, Long.MAX_VALUE);
}
/**
* Lazily reads the sequence file as and when the records are consumed from
* the returned iterator
* @param path - sequence file path
* @param start - the starting record number
* @param limit - number of records to read
* @return Iterator of Writable list which stores key and value in first two indices
* @throws IOException when an error occurs
*/
public static RecordIterator getRecordIterator(
String path, long start, long limit) throws IOException{
Path file = new Path(path);
System.out.println("Creating document stream from : " + file);
SequenceFile.Reader reader = new SequenceFile.Reader(conf, SequenceFile.Reader.file(file));
return new RecordIterator(reader, start, limit);
}
public static long count(String path) throws IOException {
//read rows between start and stop
Path file = new Path(path);
System.out.println(file);
SequenceFile.Reader reader = new SequenceFile.Reader(conf, SequenceFile.Reader.file(file));
Writable key = (Writable)
ReflectionUtils.newInstance(reader.getKeyClass(), conf);
Writable value = (Writable)
ReflectionUtils.newInstance(reader.getValueClass(), conf);
//skip rows
long i = 0;
while(reader.next(key, value)) {
i += 1;
}
return i;
}
}