问题
I'm having a strange issue with marshalling/unmarshalling an avro generated class. The error I'm getting is throwing a not an enum error - except there aren't any enum's in my class.
The error is specifically this:
com.fasterxml.jackson.databind.JsonMappingException: Not an enum: {"type":"record","name":"TimeUpdateTopic","namespace":"org.company.mmd.time","fields":[{"name":"time","type":"double"}]} (through reference chain: org.company.mmd.time.TimeUpdateTopic["schema"]->org.apache.avro.Schema$RecordSchema["enumDefault"])
Test Case
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule
import org.junit.Test
class TimeUpdateTopicTest {
val objectMapper = ObjectMapper().registerModule(JavaTimeModule())
@Test
fun decode() {
val t = TimeUpdateTopic(1.0)
objectMapper.writeValueAsString(t)
}
}
AVDL
@namespace("org.company.mmd.time")
protocol TimeMonitor {
record TimeUpdateTopic {
double time;
}
}
Java class generated by the avro task
/**
* Autogenerated by Avro
*
* DO NOT EDIT DIRECTLY
*/
package org.company.mmd.time;
import org.apache.avro.generic.GenericArray;
import org.apache.avro.specific.SpecificData;
import org.apache.avro.util.Utf8;
import org.apache.avro.message.BinaryMessageEncoder;
import org.apache.avro.message.BinaryMessageDecoder;
import org.apache.avro.message.SchemaStore;
@org.apache.avro.specific.AvroGenerated
public class TimeUpdateTopic extends org.apache.avro.specific.SpecificRecordBase implements org.apache.avro.specific.SpecificRecord {
private static final long serialVersionUID = -4648318619505855037L;
public static final org.apache.avro.Schema SCHEMA$ = new org.apache.avro.Schema.Parser().parse("{\"type\":\"record\",\"name\":\"TimeUpdateTopic\",\"namespace\":\"org.company.mmd.time\",\"fields\":[{\"name\":\"time\",\"type\":\"double\"}]}");
public static org.apache.avro.Schema getClassSchema() { return SCHEMA$; }
private static SpecificData MODEL$ = new SpecificData();
private static final BinaryMessageEncoder<TimeUpdateTopic> ENCODER =
new BinaryMessageEncoder<TimeUpdateTopic>(MODEL$, SCHEMA$);
private static final BinaryMessageDecoder<TimeUpdateTopic> DECODER =
new BinaryMessageDecoder<TimeUpdateTopic>(MODEL$, SCHEMA$);
/**
* Return the BinaryMessageEncoder instance used by this class.
* @return the message encoder used by this class
*/
public static BinaryMessageEncoder<TimeUpdateTopic> getEncoder() {
return ENCODER;
}
/**
* Return the BinaryMessageDecoder instance used by this class.
* @return the message decoder used by this class
*/
public static BinaryMessageDecoder<TimeUpdateTopic> getDecoder() {
return DECODER;
}
/**
* Create a new BinaryMessageDecoder instance for this class that uses the specified {@link SchemaStore}.
* @param resolver a {@link SchemaStore} used to find schemas by fingerprint
* @return a BinaryMessageDecoder instance for this class backed by the given SchemaStore
*/
public static BinaryMessageDecoder<TimeUpdateTopic> createDecoder(SchemaStore resolver) {
return new BinaryMessageDecoder<TimeUpdateTopic>(MODEL$, SCHEMA$, resolver);
}
/**
* Serializes this TimeUpdateTopic to a ByteBuffer.
* @return a buffer holding the serialized data for this instance
* @throws java.io.IOException if this instance could not be serialized
*/
public java.nio.ByteBuffer toByteBuffer() throws java.io.IOException {
return ENCODER.encode(this);
}
/**
* Deserializes a TimeUpdateTopic from a ByteBuffer.
* @param b a byte buffer holding serialized data for an instance of this class
* @return a TimeUpdateTopic instance decoded from the given buffer
* @throws java.io.IOException if the given bytes could not be deserialized into an instance of this class
*/
public static TimeUpdateTopic fromByteBuffer(
java.nio.ByteBuffer b) throws java.io.IOException {
return DECODER.decode(b);
}
@Deprecated public double time;
/**
* Default constructor. Note that this does not initialize fields
* to their default values from the schema. If that is desired then
* one should use <code>newBuilder()</code>.
*/
public TimeUpdateTopic() {}
/**
* All-args constructor.
* @param time The new value for time
*/
public TimeUpdateTopic(java.lang.Double time) {
this.time = time;
}
public org.apache.avro.specific.SpecificData getSpecificData() { return MODEL$; }
public org.apache.avro.Schema getSchema() { return SCHEMA$; }
// Used by DatumWriter. Applications should not call.
public java.lang.Object get(int field$) {
switch (field$) {
case 0: return time;
default: throw new org.apache.avro.AvroRuntimeException("Bad index");
}
}
// Used by DatumReader. Applications should not call.
@SuppressWarnings(value="unchecked")
public void put(int field$, java.lang.Object value$) {
switch (field$) {
case 0: time = (java.lang.Double)value$; break;
default: throw new org.apache.avro.AvroRuntimeException("Bad index");
}
}
/**
* Gets the value of the 'time' field.
* @return The value of the 'time' field.
*/
public double getTime() {
return time;
}
/**
* Sets the value of the 'time' field.
* @param value the value to set.
*/
public void setTime(double value) {
this.time = value;
}
/**
* Creates a new TimeUpdateTopic RecordBuilder.
* @return A new TimeUpdateTopic RecordBuilder
*/
public static org.company.mmd.time.TimeUpdateTopic.Builder newBuilder() {
return new org.company.mmd.time.TimeUpdateTopic.Builder();
}
/**
* Creates a new TimeUpdateTopic RecordBuilder by copying an existing Builder.
* @param other The existing builder to copy.
* @return A new TimeUpdateTopic RecordBuilder
*/
public static org.company.mmd.time.TimeUpdateTopic.Builder newBuilder(org.company.mmd.time.TimeUpdateTopic.Builder other) {
if (other == null) {
return new org.company.mmd.time.TimeUpdateTopic.Builder();
} else {
return new org.company.mmd.time.TimeUpdateTopic.Builder(other);
}
}
/**
* Creates a new TimeUpdateTopic RecordBuilder by copying an existing TimeUpdateTopic instance.
* @param other The existing instance to copy.
* @return A new TimeUpdateTopic RecordBuilder
*/
public static org.company.mmd.time.TimeUpdateTopic.Builder newBuilder(org.company.mmd.time.TimeUpdateTopic other) {
if (other == null) {
return new org.company.mmd.time.TimeUpdateTopic.Builder();
} else {
return new org.company.mmd.time.TimeUpdateTopic.Builder(other);
}
}
/**
* RecordBuilder for TimeUpdateTopic instances.
*/
public static class Builder extends org.apache.avro.specific.SpecificRecordBuilderBase<TimeUpdateTopic>
implements org.apache.avro.data.RecordBuilder<TimeUpdateTopic> {
private double time;
/** Creates a new Builder */
private Builder() {
super(SCHEMA$);
}
/**
* Creates a Builder by copying an existing Builder.
* @param other The existing Builder to copy.
*/
private Builder(org.company.mmd.time.TimeUpdateTopic.Builder other) {
super(other);
if (isValidValue(fields()[0], other.time)) {
this.time = data().deepCopy(fields()[0].schema(), other.time);
fieldSetFlags()[0] = other.fieldSetFlags()[0];
}
}
/**
* Creates a Builder by copying an existing TimeUpdateTopic instance
* @param other The existing instance to copy.
*/
private Builder(org.company.mmd.time.TimeUpdateTopic other) {
super(SCHEMA$);
if (isValidValue(fields()[0], other.time)) {
this.time = data().deepCopy(fields()[0].schema(), other.time);
fieldSetFlags()[0] = true;
}
}
/**
* Gets the value of the 'time' field.
* @return The value.
*/
public double getTime() {
return time;
}
/**
* Sets the value of the 'time' field.
* @param value The value of 'time'.
* @return This builder.
*/
public org.company.mmd.time.TimeUpdateTopic.Builder setTime(double value) {
validate(fields()[0], value);
this.time = value;
fieldSetFlags()[0] = true;
return this;
}
/**
* Checks whether the 'time' field has been set.
* @return True if the 'time' field has been set, false otherwise.
*/
public boolean hasTime() {
return fieldSetFlags()[0];
}
/**
* Clears the value of the 'time' field.
* @return This builder.
*/
public org.company.mmd.time.TimeUpdateTopic.Builder clearTime() {
fieldSetFlags()[0] = false;
return this;
}
@Override
@SuppressWarnings("unchecked")
public TimeUpdateTopic build() {
try {
TimeUpdateTopic record = new TimeUpdateTopic();
record.time = fieldSetFlags()[0] ? this.time : (java.lang.Double) defaultValue(fields()[0]);
return record;
} catch (org.apache.avro.AvroMissingFieldException e) {
throw e;
} catch (java.lang.Exception e) {
throw new org.apache.avro.AvroRuntimeException(e);
}
}
}
@SuppressWarnings("unchecked")
private static final org.apache.avro.io.DatumWriter<TimeUpdateTopic>
WRITER$ = (org.apache.avro.io.DatumWriter<TimeUpdateTopic>)MODEL$.createDatumWriter(SCHEMA$);
@Override public void writeExternal(java.io.ObjectOutput out)
throws java.io.IOException {
WRITER$.write(this, SpecificData.getEncoder(out));
}
@SuppressWarnings("unchecked")
private static final org.apache.avro.io.DatumReader<TimeUpdateTopic>
READER$ = (org.apache.avro.io.DatumReader<TimeUpdateTopic>)MODEL$.createDatumReader(SCHEMA$);
@Override public void readExternal(java.io.ObjectInput in)
throws java.io.IOException {
READER$.read(this, SpecificData.getDecoder(in));
}
@Override protected boolean hasCustomCoders() { return true; }
@Override public void customEncode(org.apache.avro.io.Encoder out)
throws java.io.IOException
{
out.writeDouble(this.time);
}
@Override public void customDecode(org.apache.avro.io.ResolvingDecoder in)
throws java.io.IOException
{
org.apache.avro.Schema.Field[] fieldOrder = in.readFieldOrderIfDiff();
if (fieldOrder == null) {
this.time = in.readDouble();
} else {
for (int i = 0; i < 1; i++) {
switch (fieldOrder[i].pos()) {
case 0:
this.time = in.readDouble();
break;
default:
throw new java.io.IOException("Corrupt ResolvingDecoder.");
}
}
}
}
}
Am I doing something stupid and/or wrong here? Or is this an actual bug
Updates
I'm able to get JSON out using this function:
inline fun <reified T: SpecificRecordBase> StringFromAvroGenerated(obj: T) : String {
val schema = obj.schema
val writer = SpecificDatumWriter(T::class.java)
val stream = ByteArrayOutputStream()
var jsonEncoder = EncoderFactory.get().jsonEncoder(schema, stream)
writer.write(obj, jsonEncoder)
jsonEncoder.flush()
return stream.toString("UTF-8")
}
but I was assuming this should be automatic with Jackson
回答1:
So it appears there are two ways to solve my issues (thanks to JsonMappingException when serializing avro generated object to json)
Write a Jackson MixIn to handle the getSchema call
So the first option required me to create a Mixin such as this:
abstract class AvroMixIn {
@JsonIgnore
abstract fun getSchema(): org.apache.avro.Schema
@JsonIgnore
abstract fun getSpecificData() : org.apache.avro.specific.SpecificData
}
And then when i make an object mapper:
val objectMapper = ObjectMapper()
.registerModule(JavaTimeModule())
.addMixIn(Object::class.java, AvroMixIn::class.java)
I chose Object::class.java instead of the actual class because it should apply to all classes. Probably a better solution is to apply it to a shared base-class all the AvroGenerated stuff has.
Rewrite the Avro Velocity Templates to automatically add this
This is actually the 1st approach I took because it seemed more "seemless".
1) Check out the avro project
2) Copy enum.vm, fixed.vm, protocol.vm, record.vm into a /avro_templates directory off the main root of my project
3) Add the @com.fasterxml.jackson.annotation.JsonIgnore property to the template:
#end
@com.fasterxml.jackson.annotation.JsonIgnore
public org.apache.avro.specific.SpecificData getSpecificData() { return MODEL$; }
@com.fasterxml.jackson.annotation.JsonIgnore
public org.apache.avro.Schema getSchema() { return SCHEMA$; }
// Used by DatumWriter. Applications should not call.
4) Update the gradle task:
avro {
dateTimeLogicalType="JSR310"
templateDirectory = "avro_templates/"
}
5) re-build avro classes
(everything now works)
来源：https://stackoverflow.com/questions/56742226/avro-generated-class-issue-with-json-conversion-kotlin