Java – Avro architecture does not respect backward compatibility
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Java
I have this Avro architecture
{ "namespace": "xx.xxxx.xxxxx.xxxxx","type": "record","name": "MyPayLoad","fields": [ {"name": "filed1","type": "string"},{"name": "filed2","type": "long"},{"name": "filed3","type": "boolean"},{ "name" : "metrics","type": { "type" : "array","items": { "name": "MyRecord","fields" : [ {"name": "min",{"name": "max",{"name": "sum",{"name": "count","type": "long"} ] } } } ] }
This is the code we use to parse the data
public static final MyPayLoad parseBinaryPayload(byte[] payload) { DatumReader<MyPayLoad> payloadReader = new SpecificDatumReader<>(MyPayLoad.class); Decoder decoder = DecoderFactory.get().binaryDecoder(payload,null); MyPayLoad myPayLoad = null; try { myPayLoad = payloadReader.read(null,decoder); } catch (IOException e) { logger.log(Level.SEVERE,e.getMessage(),e); } return myPayLoad; }
Now I want to add a field to the schema, so the schema is as follows
{ "namespace": "xx.xxxx.xxxxx.xxxxx","type": "long"} ] } } } {"name": "agentType","type": ["null","string"],"default": "APP_AGENT"} ] }
Note that the added fields also define default values The problem is, if we receive data written using the old schema, I will receive this error
java.io.EOFException: null at org.apache.avro.io.BinaryDecoder.ensureBounds(BinaryDecoder.java:473) ~[avro-1.7.4.jar:1.7.4] at org.apache.avro.io.BinaryDecoder.readInt(BinaryDecoder.java:128) ~[avro-1.7.4.jar:1.7.4] at org.apache.avro.io.BinaryDecoder.readIndex(BinaryDecoder.java:423) ~[avro-1.7.4.jar:1.7.4] at org.apache.avro.io.ResolvingDecoder.doAction(ResolvingDecoder.java:229) ~[avro-1.7.4.jar:1.7.4] at org.apache.avro.io.parsing.Parser.advance(Parser.java:88) ~[avro-1.7.4.jar:1.7.4] at org.apache.avro.io.ResolvingDecoder.readIndex(ResolvingDecoder.java:206) ~[avro-1.7.4.jar:1.7.4] at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:152) ~[avro-1.7.4.jar:1.7.4] at org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:177) ~[avro-1.7.4.jar:1.7.4] at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:148) ~[avro-1.7.4.jar:1.7.4] at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:139) ~[avro-1.7.4.jar:1.7.4] at com.appdynamics.blitz.shared.util.XXXXXXXXXXXXX.parseBinaryPayload(BlitzAvroSharedUtil.java:38) ~[blitz-shared.jar:na]
I learned from this file that this should be backward compatible, but somehow it doesn't seem so You know what I did wrong?
Solution
At last I got the job I need to give two patterns in the specificdatumreader
public static final MyPayLoad parseBinaryPayload(byte[] payload) { DatumReader<MyPayLoad> payloadReader = new SpecificDatumReader<>(SCHEMA_V1,SCHEMA_V2); Decoder decoder = DecoderFactory.get().binaryDecoder(payload,e); } return myPayLoad; }
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