Database Reference
In-Depth Information
which passes the fields of
GenericRecord
to the
Encoder
. We pass a
null
to the
encoder factory because we are not reusing a previously constructed encoder here.
In this example, only one object is written to the stream, but we could call
write()
with
more objects before closing the stream if we wanted to.
The
GenericDatumWriter
needs to be passed the schema because it follows the
schema to determine which values from the data objects to write out. After we have called
the writer's
write()
method, we flush the encoder, then close the output stream.
We can reverse the process and read the object back from the byte buffer:
DatumReader
<
GenericRecord
>
reader
=
new
GenericDatumReader
<
GenericRecord
>(
schema
);
Decoder decoder
=
DecoderFactory
.
get
().
binaryDecoder
(
out
.
toByteArray
(),
null
);
GenericRecord result
=
reader
.
read
(
null
,
decoder
);
assertThat
(
result
.
get
(
"left"
).
toString
(),
is
(
"L"
));
assertThat
(
result
.
get
(
"right"
).
toString
(),
is
(
"R"
));
We pass
null
to the calls to
binaryDecoder()
and
read()
because we are not re-
using objects here (the decoder or the record, respectively).
The objects returned by
result.get("left")
and
result.get("left")
are of
type
Utf8
, so we convert them into Java
String
objects by calling their
toString()
methods.
The Specific API
Let's look now at the equivalent code using the Specific API. We can generate the
StringPair
class from the schema file by using Avro's Maven plug-in for compiling
schemas. The following is the relevant part of the Maven Project Object Model (POM):
<project>
...
<build>
<plugins>
<plugin>
<groupId>
org.apache.avro
</groupId>
<artifactId>
avro-maven-plugin
</artifactId>
<version>
${avro.version}
</version>
<executions>
<execution>
<id>
schemas
</id>
<phase>
generate-sources
</phase>
