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Vincenz Priesnitz commented on AVRO-1341: ----------------------------------------- Thank you for the feedback. I updated the patch accordingly. > 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 > Attachments: 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. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira