/// <summary>
/// Copy a custom WrappedMapper.Context, optionally replacing
/// the input and output.
/// </summary>
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/// <param name="context">the context to clone</param>
/// <param name="conf">a new configuration</param>
/// <param name="reader">Reader to read from. Null means to clone from context.</param>
/// <param name="writer">Writer to write to. Null means to clone from context.</param>
/// <returns>a new context. it will not be the same class as the original.</returns>
/// <exception cref="System.IO.IOException"/>
/// <exception cref="System.Exception"/>
public static Mapper.Context CloneMapContext <K1, V1, K2, V2>(MapContext <K1, V1, K2
, V2> context, Configuration conf, RecordReader <K1, V1> reader, RecordWriter <K2,
V2> writer)
{
try
{
// get the outer object pointer
object outer = OuterMapField.GetValue(context);
// if it is a wrapped 21 context, unwrap it
if ("org.apache.hadoop.mapreduce.lib.map.WrappedMapper$Context".Equals(context.GetType
().FullName))
{
context = (MapContext <K1, V1, K2, V2>)WrappedContextField.GetValue(context);
}
// if the reader or writer aren't given, use the same ones
if (reader == null)
{
reader = (RecordReader <K1, V1>)ReaderField.GetValue(context);
}
if (writer == null)
{
writer = (RecordWriter <K2, V2>)WriterField.GetValue(context);
}
if (useV21)
{
object basis = MapContextImplConstructor.NewInstance(conf, context.GetTaskAttemptID
(), reader, writer, context.GetOutputCommitter(), ReporterField.GetValue(context
), context.GetInputSplit());
return((Mapper.Context)MapContextConstructor.NewInstance(outer, basis));
}
else
{
return((Mapper.Context)MapContextConstructor.NewInstance(outer, conf, context.GetTaskAttemptID
(), reader, writer, context.GetOutputCommitter(), ReporterField.GetValue(context
), context.GetInputSplit()));
}
}
catch (MemberAccessException e)
{
throw new ArgumentException("Can't access field", e);
}
catch (InstantiationException e)
{
throw new ArgumentException("Can't create object", e);
}
catch (TargetInvocationException e)
{
throw new ArgumentException("Can't invoke constructor", e);
}
}