编码对象时未使用MongoDB BSON编解码器

Question

我正在尝试将对象存储在MongoDB数据库中(使用MongoDB 3.0.2)并CodecConfigurationException在尝试使用错误消息对对象进行编码时获取

Can't find a codec for class java.time.LocalDate. 

我已经编写并包含了LocalDate对象的编解码器.细节如下.

DutyBlock我试图存储的对象具有以下成员变量:

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编码DutyBlock数据库中的对象:

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 class,我编写了以下编解码器来编码LocalDate数据库中的对象:

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);
    }
}

我在实例化MongoClient时将两个Codec(以及一个Ra类型)添加到CodecRegistryMongoClient级别.

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)
    .
    .
}

我尝试将存储ArrayList的DutyBlock对象作为一部分org.bson.DocumentMongoDB的数据库中.

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,我遇到此错误消息:

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)

LocalDate在尝试编码DutyBlock对象时似乎没有使用我的编解码器,尽管我已经验证了我试图存储的集合org.bson.Document确实包含了LocalDateCodecvia a

System.out.println(collection.getCodecRegistry().get(LocalDate.class));

任何人都可以提供一些有关这种情况发生的见解吗？

Answer 1

经过几天的研究,我找到了解决方案.

的DutyBlockCodec依赖于LocalDateCodec为了编码/解码(我创建).仅通过将两个编解码器添加到相同的编解码器注册表中就不满足此依赖性.该解决方案是通过一CodecRegistry包含该编解码器的对象DutyBlockCodec依赖于(例如,CodecRegistry在其内的含LocalDateCodec)到DutyBlockCodec的构造,它存储作为成员变量.为了使用LocalDateCodec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.另外,我写单个字段而不是写Document一个String(就像在我的原始代码中).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取决于另一个编解码器,因此需要CodecRegistry在其构造函数中传入.虽然我相信这是可能建立一个CodecRegistry与LocalDateCodec,那么通过这个作为参数传递给DutyBlockCodec的构造,然后创建另一个CodecRegistry含有LocalDateCodec和DutyBlockCodec,这是相当混乱,和MongoDB提供了功能性,CodecProvider以促进该过程.

使用CodecProvider界面,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CodecProviders使用该CodecRegistries.fromProviders()方法将这些添加到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");

我可以在https://github.com/desrepair/DutyScheduler找到这个项目的源代码. 我愿意回答人们可能遇到的任何问题.