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From Doug Cutting <cutt...@apache.org>
Subject Re: DataFileWriter/Reader vs Encoder/Decoders in Java
Date Wed, 13 Jul 2011 19:45:29 GMT
On 07/13/2011 12:15 PM, Wei Yang wrote:

> So my questions are: 1.) Is there a way to encode the schema into the
> output using the Encoder/Decoder method? 2.) Is there a way to encode
> the schema into an Json output?

One can encode the schema as a string.  What is the use case you have in
mind?

> 3.) How does the DataFileWrite/Reader,
> GenericDatumWriter/Reader and Encoder/Decoder all fit together
> architecturally?

Encoder and Decoder are the lowest level APIs.  They primarily encode
and decode primitive values.  These are not generally used directly by
applications, although an application might use them as a event-oriented
API, akin to XML's SAX.

DatumReader and DatumWriter are mid-level APIs.  They serialize and
de-serialize Java objects using an Encoder or Decoder.  Different
versions are used for different Java representations of a Schema.  These
are used by folks implementing Avro data containers, like data files or RPC.

DataFileReader and DataFileWriter are the application-level APIs.  They
permit one to read and write objects from files.

Doug

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