问题描述
我将Mongodb与Micronaut结合使用，并且读取多态Java对象给我错误，因为Mongodb无法通过类型确定具体的实现类。
myPet: { "_id" : ObjectId("5f96f4633dbd690c548c2a38"),pets: [{"type" : "Cat" },{"type" : "Dog" }]}
public class MyPet {
private List<Animal> pets = new ArrayList<Animal>(0);
public List<Animal> getPets() {
return pets;
}
public void setPets(List<Animal> pets) {
this.pets = pets;
}
}
public class Cat implements Animal {
private String type = "Cat";
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
}
public class Dog implements Animal {
private String type = "Dog";
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
}
public interface Animal {
String getType();
}
我尝试过
MongoCollection<MyPet> myPetColl = db.getCollection("myPet",MyPet.class);
myPetColl.find()
但出现错误
Unexpected error occurred: An exception occurred when decoding using the AutomaticPojoCodec.
Decoding into a 'MyPet' Failed with the following exception:
Failed to decode 'MyPet'. Decoding 'content' errored with: Cannot find a public constructor for 'Animal'.
A custom Codec or PojoCodec may need to be explicitly configured and registered to handle this type.
org.bson.codecs.configuration.CodecConfigurationException: An exception occurred when decoding using the AutomaticPojoCodec.
Decoding into a 'MyPet' Failed with the following exception:
Failed to decode 'MyPet'. Decoding 'content' errored with: Cannot find a public constructor for 'Animal'.
A custom Codec or PojoCodec may need to be explicitly configured and registered to handle this type.
at org.bson.codecs.pojo.AutomaticPojoCodec.decode(AutomaticPojoCodec.java:40)
at com.mongodb.internal.operation.CommandResultArrayCodec.decode(CommandResultArrayCodec.java:52)
at com.mongodb.internal.operation.CommandResultDocumentCodec.readValue(CommandResultDocumentCodec.java:60)
at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:84)
at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:41)
at org.bson.internal.LazyCodec.decode(LazyCodec.java:48)
at org.bson.codecs.BsonDocumentCodec.readValue(BsonDocumentCodec.java:101)
at com.mongodb.internal.operation.CommandResultDocumentCodec.readValue(CommandResultDocumentCodec.java:63)
at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:84)
at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:41)
at com.mongodb.internal.connection.ReplyMessage.<init>(ReplyMessage.java:51)
at com.mongodb.internal.connection.InternalStreamConnection.getCommandResult(InternalStreamConnection.java:412)
at com.mongodb.internal.connection.InternalStreamConnection.access$900(InternalStreamConnection.java:75)
at com.mongodb.internal.connection.InternalStreamConnection$2$1.onResult(InternalStreamConnection.java:397)
at com.mongodb.internal.connection.InternalStreamConnection$2$1.onResult(InternalStreamConnection.java:375)
at com.mongodb.internal.connection.InternalStreamConnection$MessageHeaderCallback$MessageCallback.onResult(InternalStreamConnection.java:676)
at com.mongodb.internal.connection.InternalStreamConnection$MessageHeaderCallback$MessageCallback.onResult(InternalStreamConnection.java:643)
at com.mongodb.internal.connection.InternalStreamConnection$5.completed(InternalStreamConnection.java:513)
at com.mongodb.internal.connection.InternalStreamConnection$5.completed(InternalStreamConnection.java:510)
at com.mongodb.internal.connection.AsynchronousChannelStream$BasicCompletionHandler.completed(AsynchronousChannelStream.java:230)
at com.mongodb.internal.connection.AsynchronousChannelStream$BasicCompletionHandler.completed(AsynchronousChannelStream.java:213)
at java.base/sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:127)
at java.base/sun.nio.ch.Invoker.invokeDirect(Invoker.java:158)
at java.base/sun.nio.ch.UnixAsynchronousSocketChannelImpl.implRead(UnixAsynchronousSocketChannelImpl.java:560)
at java.base/sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:277)
at java.base/sun.nio.ch.AsynchronousSocketChannelImpl.read(AsynchronousSocketChannelImpl.java:298)
at com.mongodb.internal.connection.AsynchronousSocketChannelStream$AsynchronousSocketChannelAdapter.read(AsynchronousSocketChannelStream.java:136)
at com.mongodb.internal.connection.AsynchronousChannelStream.readAsync(AsynchronousChannelStream.java:109)
at com.mongodb.internal.connection.InternalStreamConnection.readAsync(InternalStreamConnection.java:510)
at com.mongodb.internal.connection.InternalStreamConnection.access$1000(InternalStreamConnection.java:75)
at com.mongodb.internal.connection.InternalStreamConnection$MessageHeaderCallback.onResult(InternalStreamConnection.java:633)
at com.mongodb.internal.connection.InternalStreamConnection$MessageHeaderCallback.onResult(InternalStreamConnection.java:618)
at com.mongodb.internal.connection.InternalStreamConnection$5.completed(InternalStreamConnection.java:513)
at com.mongodb.internal.connection.InternalStreamConnection$5.completed(InternalStreamConnection.java:510)
at com.mongodb.internal.connection.AsynchronousChannelStream$BasicCompletionHandler.completed(AsynchronousChannelStream.java:230)
at com.mongodb.internal.connection.AsynchronousChannelStream$BasicCompletionHandler.completed(AsynchronousChannelStream.java:213)
at java.base/sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:127)
at java.base/sun.nio.ch.UnixAsynchronousSocketChannelImpl.finishRead(UnixAsynchronousSocketChannelImpl.java:437)
at java.base/sun.nio.ch.UnixAsynchronousSocketChannelImpl.finish(UnixAsynchronousSocketChannelImpl.java:191)
at java.base/sun.nio.ch.UnixAsynchronousSocketChannelImpl.onEvent(UnixAsynchronousSocketChannelImpl.java:213)
at java.base/sun.nio.ch.KQueuePort$EventHandlerTask.run(KQueuePort.java:312)
at java.base/sun.nio.ch.AsynchronousChannelGroupImpl$1.run(AsynchronousChannelGroupImpl.java:112)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
是否可以使用if-condition返回正确的类类型：
如果（obj.type ==“ Dog”）返回Dog.class，否则返回Cat.class
像杰克逊一样
@JsonTypeInfo(
use = JsonTypeInfo.Id.NAME,include = JsonTypeInfo.As.PROPERTY,property = "type")
@JsonSubTypes({
@JsonSubTypes.Type(value = Dog.class,name = "Dog"),@JsonSubTypes.Type(value = Cat.class,name = "Cat"),})
解决方法
您可以使用@BsonDiscriminator注释来告诉MongoDB驱动程序哪个字段用作鉴别键。这是一个工作示例：
import org.bson.codecs.pojo.annotations.BsonDiscriminator;
@BsonDiscriminator(key = Animal.DISCRIMINATOR_KEY)
public interface Animal {
String DISCRIMINATOR_KEY = "type";
String getType();
}
public class Cat implements Animal {
@Override
public String getType() {
return Cat.class.getName();
}
}
public class Dog implements Animal {
@Override
public String getType() {
return Dog.class.getName();
}
}
如您所见，我使用完整的类名作为type字段的值。不幸的是，自定义标识符值（不同于全类名）现在在Micronaut MongoDB Client中尚不起作用。正是由于这个问题，仍未解决：https://github.com/micronaut-projects/micronaut-mongodb/issues/10