CompressionCodecFactory returns unconfigured GZipCodec if io.compression.codecs 
is not set
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                 Key: HADOOP-7196
                 URL: https://issues.apache.org/jira/browse/HADOOP-7196
             Project: Hadoop Common
          Issue Type: Bug
    Affects Versions: 0.20.2
            Reporter: Peter Voss


In case io.compression.codecs property is not set the GZipCodec is added using 
this code:
{code:java}
List<Class<? extends CompressionCodec>> codecClasses = getCodecClasses(conf);
if (codecClasses == null) {
  addCodec(new GzipCodec());
  addCodec(new DefaultCodec());      
} else {
  Iterator<Class<? extends CompressionCodec>> itr = codecClasses.iterator();
  while (itr.hasNext()) {
    CompressionCodec codec = ReflectionUtils.newInstance(itr.next(), conf);
    addCodec(codec);     
  }
}
{code}
which leaves GzipCodec unconfigured. If it is set via the 
{{io.compression.codecs}} property it gets configured properly using 
ReflectionUtils.newInstance(..., conf).

I have seen a lot of NPEs on systems that don't have this property set when 
using a LineRecordReader (that internally gets the codec from 
CompressionCodecFactory).

I would suggest to use 
{{org.apache.hadoop.io.compress.GzipCodec,org.apache.hadoop.io.compress.DefaultCodec}}
 as default value for {{io.compression.codecs}}, instead of having another 
independent code path that deals with the case that this property is not set.

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