我正在寻找一种以通用方式将 POJO 转换为 avro 对象的方法。该实现对于 POJO 类的任何更改都应该具有鲁棒性。我已经实现了它,但明确填写了 avro 记录(请参见下面的示例)。
有没有办法摆脱硬编码的字段名称,只从对象中填充 avro 记录?反射是唯一的方法吗?或者 avro 是否提供了开箱即用的此功能?
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
import org.apache.avro.Schema;
import org.apache.avro.generic.GenericData.Record;
import org.apache.avro.reflect.ReflectData;
public class PojoToAvroExample {
static class PojoParent {
public final Map<String, String> aMap = new HashMap<String, String>();
public final Map<String, Integer> anotherMap = new HashMap<String, Integer>();
}
static class Pojo extends PojoParent {
public String uid;
public Date eventTime;
}
static Pojo createPojo() {
Pojo foo = new Pojo();
foo.uid = "123";
foo.eventTime = new Date();
foo.aMap.put("key", "val");
foo.anotherMap.put("key", 42);
return foo;
}
public static void main(String[] args) {
// extract the avro schema corresponding to Pojo class
Schema schema = ReflectData.get().getSchema(Pojo.class);
System.out.println("extracted avro schema: " + schema);
// create avro record corresponding to schema
Record avroRecord = new Record(schema);
System.out.println("corresponding empty avro record: " + avroRecord);
Pojo foo = createPojo();
// TODO: to be replaced by generic variant:
// something like avroRecord.importValuesFrom(foo);
avroRecord.put("uid", foo.uid);
avroRecord.put("eventTime", foo.eventTime);
avroRecord.put("aMap", foo.aMap);
avroRecord.put("anotherMap", foo.anotherMap);
System.out.println("expected avro record: " + avroRecord);
}
}
你用的是Spring吗?
我使用 Spring 功能为此构建了一个映射器。但也可以通过原始反射工具构建这样的映射器:
import org.apache.avro.Schema;
import org.apache.avro.generic.GenericData;
import org.apache.avro.reflect.ReflectData;
import org.springframework.beans.PropertyAccessorFactory;
import org.springframework.util.Assert;
public class GenericRecordMapper {
public static GenericData.Record mapObjectToRecord(Object object) {
Assert.notNull(object, "object must not be null");
final Schema schema = ReflectData.get().getSchema(object.getClass());
final GenericData.Record record = new GenericData.Record(schema);
schema.getFields().forEach(r -> record.put(r.name(), PropertyAccessorFactory.forDirectFieldAccess(object).getPropertyValue(r.name())));
return record;
}
public static <T> T mapRecordToObject(GenericData.Record record, T object) {
Assert.notNull(record, "record must not be null");
Assert.notNull(object, "object must not be null");
final Schema schema = ReflectData.get().getSchema(object.getClass());
Assert.isTrue(schema.getFields().equals(record.getSchema().getFields()), "Schema fields didn't match");
record.getSchema().getFields().forEach(d -> PropertyAccessorFactory.forDirectFieldAccess(object).setPropertyValue(d.name(), record.get(d.name()) == null ? record.get(d.name()) : record.get(d.name()).toString()));
return object;
}
}
使用此映射器,您可以生成一个 GenericData.Record,它可以轻松序列化为 avro。当您反序列化 Avro ByteArray 时,您可以使用它从反序列化记录重建 POJO:
连载
byte[] serialized = avroSerializer.serialize("topic", GenericRecordMapper.mapObjectToRecord(yourPojo));
反序列化
GenericData.Record deserialized = (GenericData.Record) avroDeserializer.deserialize("topic", serialized);
YourPojo yourPojo = GenericRecordMapper.mapRecordToObject(deserialized, new YourPojo());
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