我正在尝试将对象存储在 MongoDB 数据库中(使用 MongoDB 3.0.2)，并在尝试使用错误消息对对象进行编码时收到 CodecConfigurationException
Can't find a codec for class java.time.LocalDate.
我已经为 LocalDate 对象编写并包含了一个编解码器。详情如下。
我尝试存储的对象 DutyBlock 具有以下成员变量:
public class DutyBlock {
private LocalDate startDate;
private LocalDate endDate; //Inclusive
private int blockLength;
private double pointValue;
private ArrayList<Ra> assigned;
}
我编写了以下编解码器来对数据库中的 DutyBlock 对象进行编码:
public class DutyBlockCodec implements Codec<DutyBlock> {
@Override
public void encode(BsonWriter writer, DutyBlock t, EncoderContext ec) {
Document document = new Document();
document.append("startDate", t.getStartDate());
document.append("endDate", t.getEndDate());
document.append("blockLength", t.getBlockLength());
document.append("pointValue", t.getPointValue());
document.append("assigned", t.getRasOnDuty());
writer.writeString(document.toJson()); //Line 27 in the error message.
}
@Override
public Class<DutyBlock> getEncoderClass() {
return DutyBlock.class;
}
@Override
public DutyBlock decode(BsonReader reader, DecoderContext dc) {
String json = reader.readString();
return new DutyBlock(Document.parse(json));
}
}
由于 MongoDB 目前不支持 java.time.LocalDate 类，我编写了以下编解码器来编码数据库中的 LocalDate 对象:
public class LocalDateCodec implements Codec<LocalDate> {
@Override
public void encode(BsonWriter writer, LocalDate t, EncoderContext ec) {
writer.writeString(t.toString());
}
@Override
public Class<LocalDate> getEncoderClass() {
return LocalDate.class;
}
@Override
public LocalDate decode(BsonReader reader, DecoderContext dc) {
String date = reader.readString();
return LocalDate.parse(date);
}
}
我已将两个 Codec(以及一个用于 Ra 类型的)添加到 MongoClient 级别的 CodecRegistry，同时实例化 MongoClient。
public class DutyScheduleDB {
private MongoClient mongoClient;
private MongoDatabase db;
public DutyScheduleDB() {
CodecRegistry codecRegistry =
CodecRegistries.fromRegistries(
CodecRegistries.fromCodecs(new LocalDateCodec(), new DutyBlockCodec(), new RaCodec()),
MongoClient.getDefaultCodecRegistry());
MongoClientOptions options = MongoClientOptions.builder()
.codecRegistry(codecRegistry).build();
mongoClient = new MongoClient(new ServerAddress(), options);
db = mongoClient.getDatabase("DutySchedulerDB");
}
. (More code not shown)
.
.
}
我尝试将 DutyBlock 对象的 ArrayList 作为 org.bson.Document 的一部分存储在 MongoDB 数据库中。
public void storeScheduledCalendar(String id,
String calendarName,
ArrayList<DutyBlock> cal) {
//Access collection of scheduled calendars.
MongoCollection collection = db.getCollection("ScheduledCalendars");
//Query parameter is uuid + calendarName.
Document doc = new Document("name", id + calendarName);
doc.append("dutyBlocks", cal);
//Insert doc to collection.
collection.insertOne(doc); //Line 59 in the error message.
}
但是，我遇到了这个错误消息:
Exception in thread "main" org.bson.codecs.configuration.CodecConfigurationException: Can't find a codec for class java.time.LocalDate.
at org.bson.codecs.configuration.CodecCache.getOrThrow(CodecCache.java:46)
at org.bson.codecs.configuration.ProvidersCodecRegistry.get(ProvidersCodecRegistry.java:63)
at org.bson.codecs.configuration.ProvidersCodecRegistry.get(ProvidersCodecRegistry.java:37)
at org.bson.codecs.DocumentCodec.writeValue(DocumentCodec.java:174)
at org.bson.codecs.DocumentCodec.writeMap(DocumentCodec.java:189)
at org.bson.codecs.DocumentCodec.encode(DocumentCodec.java:131)
at org.bson.codecs.DocumentCodec.encode(DocumentCodec.java:45)
at org.bson.Document.toJson(Document.java:294)
at org.bson.Document.toJson(Document.java:268)
at org.bson.Document.toJson(Document.java:255)
at SchedulingHeuristic.DutyBlockCodec.encode(DutyBlockCodec.java:27)
at SchedulingHeuristic.DutyBlockCodec.encode(DutyBlockCodec.java:16)
at org.bson.codecs.EncoderContext.encodeWithChildContext(EncoderContext.java:91)
at org.bson.codecs.DocumentCodec.writeValue(DocumentCodec.java:175)
at org.bson.codecs.DocumentCodec.writeIterable(DocumentCodec.java:197)
at org.bson.codecs.DocumentCodec.writeValue(DocumentCodec.java:170)
at org.bson.codecs.DocumentCodec.writeMap(DocumentCodec.java:189)
at org.bson.codecs.DocumentCodec.encode(DocumentCodec.java:131)
at org.bson.codecs.DocumentCodec.encode(DocumentCodec.java:45)
at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:63)
at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:29)
at com.mongodb.connection.InsertCommandMessage.writeTheWrites(InsertCommandMessage.java:99)
at com.mongodb.connection.InsertCommandMessage.writeTheWrites(InsertCommandMessage.java:43)
at com.mongodb.connection.BaseWriteCommandMessage.encodeMessageBody(BaseWriteCommandMessage.java:112)
at com.mongodb.connection.BaseWriteCommandMessage.encodeMessageBody(BaseWriteCommandMessage.java:35)
at com.mongodb.connection.RequestMessage.encode(RequestMessage.java:132)
at com.mongodb.connection.BaseWriteCommandMessage.encode(BaseWriteCommandMessage.java:89)
at com.mongodb.connection.WriteCommandProtocol.sendMessage(WriteCommandProtocol.java:170)
at com.mongodb.connection.WriteCommandProtocol.execute(WriteCommandProtocol.java:73)
at com.mongodb.connection.InsertCommandProtocol.execute(InsertCommandProtocol.java:66)
at com.mongodb.connection.InsertCommandProtocol.execute(InsertCommandProtocol.java:37)
at com.mongodb.connection.DefaultServer$DefaultServerProtocolExecutor.execute(DefaultServer.java:155)
at com.mongodb.connection.DefaultServerConnection.executeProtocol(DefaultServerConnection.java:219)
at com.mongodb.connection.DefaultServerConnection.insertCommand(DefaultServerConnection.java:108)
at com.mongodb.operation.MixedBulkWriteOperation$Run$2.executeWriteCommandProtocol(MixedBulkWriteOperation.java:416)
at com.mongodb.operation.MixedBulkWriteOperation$Run$RunExecutor.execute(MixedBulkWriteOperation.java:604)
at com.mongodb.operation.MixedBulkWriteOperation$Run.execute(MixedBulkWriteOperation.java:363)
at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:148)
at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:141)
at com.mongodb.operation.OperationHelper.withConnectionSource(OperationHelper.java:186)
at com.mongodb.operation.OperationHelper.withConnection(OperationHelper.java:177)
at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:141)
at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:72)
at com.mongodb.Mongo.execute(Mongo.java:747)
at com.mongodb.Mongo$2.execute(Mongo.java:730)
at com.mongodb.MongoCollectionImpl.executeSingleWriteRequest(MongoCollectionImpl.java:482)
at com.mongodb.MongoCollectionImpl.insertOne(MongoCollectionImpl.java:277)
at DutyScheduleDB.storeScheduledCalendar(DutyScheduleDB.java:59)
at DutyScheduleDB.main(DutyScheduleDB.java:106)
在尝试对 DutyBlock 对象进行编码时，似乎没有使用我的 LocalDate 编解码器，尽管我已经验证了我正在尝试存储的集合org.bson.Document 确实包含 LocalDateCodec 通过
System.out.println(collection.getCodecRegistry().get(LocalDate.class));
谁能提供一些关于为什么会发生这种情况的见解？
最佳答案
经过几天的研究，我想出了一个解决方案。
DutyBlockCodec 依赖于 LocalDateCodec(我创建的)以进行编码/解码。仅仅通过将两个编解码器添加到同一个编解码器注册表中并不能满足这种依赖关系。解决方案是传递一个 CodecRegistry 对象，该对象包含 DutyBlockCodec 所依赖的编解码器(例如，一个 CodecRegistry 在其中包含 LocalDateCodec) 到 DutyBlockCodec 的构造函数，该构造函数存储为成员变量。为了使用 LocalDateCodec 进行编码，我使用 EncoderContext.encodeWithChildContext() 方法，传入编解码器、编写器和元素进行编码。此外，我编写单独的字段，而不是将 Document 编写为 String(就像我的原始代码一样)。因此 DutyBlock 编解码器最终看起来像这样:
public class DutyBlockCodec implements Codec<DutyBlock> {
private final CodecRegistry codecRegistry;
public DutyBlockCodec(final CodecRegistry codecRegistry) {
this.codecRegistry = codecRegistry;
}
@Override
public void encode(BsonWriter writer, DutyBlock t, EncoderContext ec) {
writer.writeStartDocument();
Codec dateCodec = codecRegistry.get(LocalDate.class);
writer.writeName("startDate");
ec.encodeWithChildContext(dateCodec, writer, t.getStartDate());
writer.writeName("endDate");
ec.encodeWithChildContext(dateCodec, writer, t.getEndDate());
writer.writeName("blockLength");
writer.writeInt32(t.getBlockLength());
writer.writeName("pointValue");
writer.writeDouble(t.getPointValue());
//Writing ArrayList of RAs
writer.writeName("assigned");
writer.writeStartArray();
for (Ra ra : t.getRasOnDuty()) {
Codec raCodec = codecRegistry.get(Ra.class);
ec.encodeWithChildContext(raCodec, writer, ra);
}
writer.writeEndArray();
writer.writeEndDocument();
}
@Override
public Class<DutyBlock> getEncoderClass() {
return DutyBlock.class;
}
@Override
public DutyBlock decode(BsonReader reader, DecoderContext dc) {
reader.readStartDocument();
Codec<LocalDate> dateCodec = codecRegistry.get(LocalDate.class);
reader.readName();
LocalDate startDate = dateCodec.decode(reader, dc);
reader.readName();
LocalDate endDate = dateCodec.decode(reader, dc);
reader.readName();
int blockLength = reader.readInt32();
reader.readName();
double pointValue = reader.readDouble();
//Reading ArrayList of RAs
reader.readName();
Codec<Ra> raCodec = codecRegistry.get(Ra.class);
ArrayList<Ra> rasOnDuty = new ArrayList<>();
reader.readStartArray();
while (reader.readBsonType() != BsonType.END_OF_DOCUMENT) {
rasOnDuty.add(raCodec.decode(reader, dc));
}
reader.readEndArray();
reader.readEndDocument();
return new DutyBlock(startDate, endDate, blockLength, pointValue, rasOnDuty);
}
}
DutyBlockCodec 依赖于另一个编解码器，因此需要在其构造函数中传入 CodecRegistry。虽然我相信可以使用 LocalDateCodec 创建一个 CodecRegistry，然后将其作为参数传递给 DutyBlockCodec 的构造函数，然后创建另一个CodecRegistry 同时包含 LocalDateCodec 和 DutyBlockCodec，这样比较困惑，而 MongoDB 提供了一个功能，CodecProvider 方便这个过程。
使用CodecProvider接口(interface)，我写了一个DutyBlockCodecProvider
public class DutyBlockCodecProvider implements CodecProvider {
@Override
public <T> Codec<T> get(Class<T> type, CodecRegistry cr) {
if (type == DutyBlock.class) {
return (Codec<T>) new DutyBlockCodec(cr);
}
return null;
}
}
我使用 CodecRegistries.fromProviders() 方法将这些 CodecProviders 添加到 MongoDB 客户端。
CodecRegistry codecRegistry = CodecRegistries.fromRegistries(
CodecRegistries.fromCodecs(new LocalDateCodec()),
CodecRegistries.fromProviders(
new RaCodecProvider(),
new DutyBlockCodecProvider(),
new ScheduledDutyCodecProvider()),
MongoClient.getDefaultCodecRegistry());
MongoClientOptions options = MongoClientOptions.builder()
.codecRegistry(codecRegistry).build();
mongoClient = new MongoClient(new ServerAddress(), options);
db = mongoClient.getDatabase("DutySchedulerDB");
我的这个项目的源代码可以在 https://github.com/desrepair/DutyScheduler 找到 我愿意回答人们可能提出的任何问题。
关于java - 编码对象时未使用 MongoDB BSON 编解码器，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30569228/