The class implementing Writable should provide a public default constructor.
On Tue, May 11, 2010 at 7:20 AM, Ananth Sarathy <[email protected]>wrote: > 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 > > > > > >
