Yeah, no I get that. But when you use the sequence file reader example from
The Hadoop The Defintive Guide book page 106
reader = new SequenceFile.Reader(fs, path, conf);
System.out.println(reader.getKeyClass());
System.out.println(reader.getValueClass());
Writable key = (Writable) ReflectionUtils.newInstance(reader
.getKeyClass(), conf);
Writable val = (Writable) ReflectionUtils.newInstance(reader
.getValueClass(), conf);
LuceneDocumentWrapper ldw = null;
long position = reader.getPosition();
while (reader.next(key, val)) {
ldw = (LuceneDocumentWrapper) val;
System.out.println(ldw.get());
}
But when using a LuceneDocumentWrapper which uses the interface, I get this
error
java.lang.RuntimeException: java.lang.NoSuchMethodException:
org.apache.hadoop.hbase.mapreduce.LuceneDocumentWrapper.<init>()
at
org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:115)
at
com.iswcorp.mapreduce.test.SequenceFileReaderTest.main(SequenceFileReaderTest.java:39)
Caused by: java.lang.NoSuchMethodException:
org.apache.hadoop.hbase.mapreduce.LuceneDocumentWrapper.<init>()
at java.lang.Class.getConstructor0(Class.java:2706)
Caused by this line Writable val = (Writable)
ReflectionUtils.newInstance(reader
.getValueClass(), conf);
which has to do with not having a default constructor, which is why I asked
the orginal question. Is there some other way to get the values out?
Ananth T Sarathy
On Mon, May 10, 2010 at 11:46 PM, Ted Yu <[email protected]> wrote:
> Writable is the recommended interface to work with.
> Writable implementations reuse instances which serves large scale data
> processing better than JavaSerialization.
>
> Cheers
>
> On Mon, May 10, 2010 at 6:29 PM, Ananth Sarathy
> <[email protected]>wrote:
>
> > My team and I were working with sequence files and were using the
> > LuceneDocumentWrapper. But when I try to get the valcall, i get a no such
> > method exception from the ReflectionUtils, which is caused because it's
> > trying to call a default constructor which doesn't exist for that class.
> >
> > So my question is whether there is documentation or limitations to the
> > type
> > of objects that can be used with a sequencefile other than the Writable
> > interface? I want to know if maybe I am trying to read from the file in
> the
> > wrong way.
> > Ananth T Sarathy
> >
>
