java - Sequence Files in Hadoop -

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how these sequence files generated ? saw link sequence file here, 

http://wiki.apache.org/hadoop/sequencefile

are these written using default java serializer ? , how read sequence file ?

sequence files generated mapreduce tasks , and can used common format transfer data between mapreduce jobs.

you can read them in following manner:

configuration config = new configuration(); path path = new path(path_to_your_file); sequencefile.reader reader = new sequencefile.reader(filesystem.get(config), path, config); writablecomparable key = (writablecomparable) reader.getkeyclass().newinstance(); writable value = (writable) reader.getvalueclass().newinstance(); while (reader.next(key, value))   // perform operating reader.close();

also can generate sequence files using sequencefile.writer.

the classes used in example following:

import org.apache.hadoop.conf.configuration; import org.apache.hadoop.fs.filesystem; import org.apache.hadoop.fs.path; import org.apache.hadoop.io.sequencefile; import org.apache.hadoop.io.writable; import org.apache.hadoop.io.writablecomparable;

and contained within hadoop-core maven dependency:

<dependency>     <groupid>org.apache.hadoop</groupid>     <artifactid>hadoop-core</artifactid>     <version>1.2.1</version> </dependency>

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