JsonMappingException when serializing avro generated object to json

问题

I used avro-tools to generate java classes from avsc files, using:

java.exe -jar avro-tools-1.7.7.jar compile -string schema myfile.avsc

Then I tried to serialize such objects to json by ObjectMapper, but always got a JsonMappingException saying "not an enum" or "not a union". In my test I create the generated object using it's builder or constructor. I got such exceptions for objects of different classes...

Sample Code:

ObjectMapper serializer = new ObjectMapper(); // com.fasterxml.jackson.databind
serializer.register(new JtsModule()); // com.bedatadriven.jackson.datatype.jts
...
return serializer.writeValueAsBytes(avroConvertedObject); // => JsonMappingException

I also tried many configurations using: serializer.configure(...) but still failed. Versions: Java 1.8, jackson-datatype-jts 2.3, jackson-core 2.6.5, jackson-databind 2.6.5, jackson-annotations 2.6.5

Any suggestions? Thanks!

回答1:

If the SCHEMA member is really the case (we don't see the full error message), then you can switch it off. I use a mixin to do it, like this:

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import org.apache.avro.Schema;
import org.junit.Test;

import java.io.File;
import java.io.IOException;

public class AvroGenerTests
{
  abstract class IgnoreSchemaProperty
  {
    // You have to use the correct package for JsonIgnore,
    // fasterxml or codehaus
    @JsonIgnore abstract void getSchema();
  }

  @Test
  public void writeJson() throws IOException {
    BookAvro b = BookAvro.newBuilder()
      .setTitle("Wilk stepowy")
      .setAuthor("Herman Hesse")
      .build();
    ObjectMapper om = new ObjectMapper();
    om.enable(SerializationFeature.INDENT_OUTPUT);
    om.addMixIn(BookAvro.class, IgnoreSchemaProperty.class);
    om.writeValue(new File("plik_z_gen.json"), b);
  }
}

来源：https://stackoverflow.com/questions/39349733/jsonmappingexception-when-serializing-avro-generated-object-to-json

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java

json

serialization

avro