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https://issues.apache.org/jira/browse/AVRO-1341?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14393138#comment-14393138
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Ryan Blue commented on AVRO-1341:
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[~sunzhaonan], there isn't an @AvroDoc annotation, but its a great idea. Could
you open an issue to add it? It shouldn't be too much work, either.
> Allow controlling avro via java annotations when using reflection.
> -------------------------------------------------------------------
>
> Key: AVRO-1341
> URL: https://issues.apache.org/jira/browse/AVRO-1341
> Project: Avro
> Issue Type: New Feature
> Components: java
> Reporter: Vincenz Priesnitz
> Assignee: Vincenz Priesnitz
> Fix For: 1.7.5
>
> Attachments: AVRO-1341.patch, AVRO-1341.patch, AVRO-1341.patch,
> AVRO-1341.patch, AVRO-1341.patch, AVRO-1341.patch, AVRO-1341.patch
>
>
> It would be great if one could control avro with java annotations. As of now,
> it is already possible to mark fields as Nullable or classes being encoded as
> a String. I propose a bigger set of annotations to control the behavior of
> avro on fields and classes. Such annotations have proven useful with jacksons
> json serialization and morphias mongoDB serialization.
> I propose the following additional annotations:
> @AvroName("alternativeName")
> @AvroAlias(alias="alias", space="space")
> @AvroIgnore
> @AvroMeta(key="K", value="V")
> @AvroEncode(using=CustomEncoding.class)
> Java fields with the @AvroName("alternativeName") annotation will be renamed
> in the induced schema. When reading an avro file via reflection, the
> reflection reader will look for fields in the schema with "alternativeName".
> For example:
> {code}
> @AvroName("foo")
> int bar;
> {code}
> is serialized as
> {code}
> { "name" : "foo", "type" : "int" }
> {code}
> The @AvroAlias annotation will add a new alias to the induced schema of a
> record, enum or field. The space parameter is optional and defaults to the
> namespace of the named schema the alias is added to.
> Fields with the @AvroIgnore annotation will be treated as if they had a
> transient modifier, i.e. they will not be written to or read from avro files.
> The @AvroMeta(key="K", value="V") annotation allows you to store an arbitrary
> key : value pair at every node in the schema.
> {code}
> @AvroMeta(key="fieldKey", value="fieldValue")
> int foo;
> {code}
> will create the following schema
> {code}
> {"name" : "foo", "type" : "int", "fieldKey" : "fieldValue" }
> {code}
> Fields can be custom encoded with the AvroEncode(using=CustomEncoding.class)
> annotation. This annotation is a generalization of the @Stringable
> annotation. The @Stringable annotation is limited to classes with string
> argument constructors. Some classes can be similarly reduced to a smaller
> class or even a single primitive, but dont fit the requirements for
> @Stringable. A prominent example is java.util.Date, which instances can
> essentially be described with a single long. Such classes can now be encoded
> with a CustomEncoding, which reads and writes directly from the
> encoder/decoder.
> One simply extends the abstract CustomEncodings class by implementing a
> schema, a read method and a write method. A java field can then be annotated
> like this:
> {code}
> @AvroEncode(using=DateAslongEncoding.class)
> Date date;
> {code}
> The custom encoding implementation would look like
> {code}
> public class DateAsLongEncoding extends CustomEncoding<Date> {
> {
> schema = Schema.create(Schema.Type.LONG);
> schema.addProp("CustomEncoding", "DateAsLongEncoding");
> }
>
> @Override
> public void write(Object datum, Encoder out) throws IOException {
> out.writeLong(((Date)datum).getTime());
> }
>
> @Override
> public Date read(Object reuse, Decoder in) throws IOException {
> if (reuse != null) {
> ((Date)reuse).setTime(in.readLong());
> return (Date)reuse;
> }
> else return new Date(in.readLong());
> }
> }
> {code}
> I implemented said annotations and a custom encoding for java.util.Date as a
> proof of concept and also extended the @Stringable annotations to fields.
> This issue is a followup of AVRO-1328 and AVRO-1330.
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