我有一个POJO类,看起来像这样-
public class CacheEntity<V> {
private String cacheId;
private V value;
public static final String ID_KEY = "cacheId";
public CacheEntity() {
}
public CacheEntity(String cache_id, V value) {
this.cacheId = cache_id;
this.value = value;
}
public V getValue() {
return value;
}
public void setValue(V value) {
this.value = value;
}
public String getCacheId() {
return cacheId;
}
public void setCacheId(String cacheId) {
this.cacheId = cacheId;
}
}
我使用的是官方驱动mongodb- driver -sync版本3.8.1
正如文档here中所提到的,我将CodecRegistry与automatic PojoCodecProvider结合使用。当我试图持久化这个实体时,我得到了以下错误。
Exception in thread "main" org.bson.codecs.configuration.CodecConfigurationException: CacheEntity contains generic types that have not been specialised.
Top level classes with generic types are not supported by the PojoCodec.
at org.bson.codecs.pojo.PojoCodecImpl.encode(PojoCodecImpl.java:93)
at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:63)
at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:29)
at com.mongodb.operation.BulkWriteBatch$WriteRequestEncoder.encode(BulkWriteBatch.java:398)
at com.mongodb.operation.BulkWriteBatch$WriteRequestEncoder.encode(BulkWriteBatch.java:377)
at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:63)
at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:29)
at com.mongodb.internal.connection.BsonWriterHelper.writeDocument(BsonWriterHelper.java:75)
at com.mongodb.internal.connection.BsonWriterHelper.writePayload(BsonWriterHelper.java:59)
at com.mongodb.internal.connection.CommandMessage.encodeMessageBodyWithMetadata(CommandMessage.java:143)
at com.mongodb.internal.connection.RequestMessage.encode(RequestMessage.java:138)
at com.mongodb.internal.connection.CommandMessage.encode(CommandMessage.java:57)
at com.mongodb.internal.connection.InternalStreamConnection.sendAndReceive(InternalStreamConnection.java:244)
at com.mongodb.internal.connection.UsageTrackingInternalConnection.sendAndReceive(UsageTrackingInternalConnection.java:99)
at com.mongodb.internal.connection.DefaultConnectionPool$PooledConnection.sendAndReceive(DefaultConnectionPool.java:444)
at com.mongodb.internal.connection.CommandProtocolImpl.execute(CommandProtocolImpl.java:72)
at com.mongodb.internal.connection.DefaultServer$DefaultServerProtocolExecutor.execute(DefaultServer.java:200)
at com.mongodb.internal.connection.DefaultServerConnection.executeProtocol(DefaultServerConnection.java:269)
at com.mongodb.internal.connection.DefaultServerConnection.command(DefaultServerConnection.java:131)
at com.mongodb.operation.MixedBulkWriteOperation.executeCommand(MixedBulkWriteOperation.java:418)
at com.mongodb.operation.MixedBulkWriteOperation.executeBulkWriteBatch(MixedBulkWriteOperation.java:256)
at com.mongodb.operation.MixedBulkWriteOperation.access$700(MixedBulkWriteOperation.java:67)
at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:200)
at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:191)
at com.mongodb.operation.OperationHelper.withReleasableConnection(OperationHelper.java:419)
at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:191)
at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:67)
at com.mongodb.client.internal.MongoClientDelegate$DelegateOperationExecutor.execute(MongoClientDelegate.java:193)
at com.mongodb.client.internal.MongoCollectionImpl.executeSingleWriteRequest(MongoCollectionImpl.java:960)
at com.mongodb.client.internal.MongoCollectionImpl.executeReplaceOne(MongoCollectionImpl.java:602)
at com.mongodb.client.internal.MongoCollectionImpl.replaceOne(MongoCollectionImpl.java:578)
at com.mongodb.client.internal.MongoCollectionImpl.replaceOne(MongoCollectionImpl.java:567)
我能做些什么来让它工作呢?谢谢。
发布于 2019-06-06 03:36:55
有以下几个选项可以让它工作。
通过子类化
如果你每次都用具体的泛型类型子类化,它就会起作用:
public class MyClassCacheEntity extends CacheEntity<MyClass> {}
通过使用BsonDocument
+ Jackson
为了避免子类化,您可以尝试将任意对象存储为BsonDocument
-s,并使用Jackson序列化/反序列化它们:
public class CacheEntity<V> {
private String cacheId;
private BsonDocument rawValue;
// [...]
// sets the value
public void withValue(T o) {
this.rawValue = BsonDocument.parse(new ObjectMapper().writeValueAsString(o))
}
// recovers the value
public T value(Class<T> clazz) {
return new ObjectMapper().readValue(this.rawValue.toJson(), clazz);
}
}
除非您避免使用withValue()
和value()
方法的getters/setters约定,否则Mongo会开始抱怨同样的泛型问题。
与纯bson相同
我认为,您也可以尝试使用org.bson.codecs.pojo.PojoCodec
来完成上述操作,您可以从当前的mongo编解码器注册表中创建或提取它。如果你提前知道并给它真正的类,它就不应该抱怨泛型。
https://stackoverflow.com/questions/52197137
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