I have been trying to understand how to write a simple custom writable class
and I find the documentation available very vague and unclear about certain
things. okay so here is the sample writable implementation in javadoc of
Writable interface
public class MyWritable implements Writable {
// Some data
private int counter;
private long timestamp;
*public void write(DataOutput out) throws IOException {
out.writeInt(counter);
out.writeLong(timestamp);
}*
* public void readFields(DataInput in) throws IOException {
counter = in.readInt();
timestamp = in.readLong();
}*
public static MyWritable read(DataInput in) throws IOException {
MyWritable w = new MyWritable();
w.readFields(in);
return w;
}
}
so in readFields function we are simply saying read an int from the
datainput and put that in counter .. and then read a long and put that in
timestamp variable .. what doesnt makes sense to me is what is the format of
DataInput here .. what if there are multiple ints and multiple longs .. how
is the correct int gonna go in counter .. what if the data I am reading in
my mapper is a string line .. and I am using regular expression to parse the
tokens .. how do I specify which field goes where .. simply saying readInt
or readText .. how does that gets connected to the right stuff ..
so in my case like I said I am reading from iis log files where my mapper
input is a log line which contains usual log information like data, time,
user, server, url, qry, responseTme etc .. I want to parse these into an
object that can be passed to reducer instead of dumping all that information
as text ..
I would appreciate any help.
Thanks
Adeel
