MongoDB 3.0 java driver Codec example - Codec class for the mapping the Grades bean

GradesCodec.java

package org.scratch;

import org.bson.BsonReader;
import org.bson.BsonString;
import org.bson.BsonValue;
import org.bson.BsonWriter;
import org.bson.Document;
import org.bson.codecs.Codec;
import org.bson.codecs.CollectibleCodec;
import org.bson.codecs.DecoderContext;
import org.bson.codecs.DocumentCodec;
import org.bson.codecs.EncoderContext;
import org.bson.types.ObjectId;

public class GradesCodec implements CollectibleCodec<Grades> {

	private Codec<Document> documentCodec;

	public GradesCodec() {
		this.documentCodec = new DocumentCodec();
	}

	public GradesCodec(Codec<Document> codec) {
		this.documentCodec = codec;
	}

	@Override
	public void encode(BsonWriter writer, Grades value,
			EncoderContext encoderContext) {
		Document document = new Document();

		ObjectId id = value.getId();
		Double score = value.getScore();
		Integer studentId = value.getStudentId();
		String type = value.getType();

		if (null != id) {
			document.put("_id", id);
		}

		if (null != score) {
			document.put("score", score);
		}

		if (null != studentId) {
			document.put("student_id", studentId);
		}
		if (null != type) {
			document.put("type", type);
		}

		documentCodec.encode(writer, document, encoderContext);

	}

	@Override
	public Class<Grades> getEncoderClass() {
		return Grades.class;
	}

	@Override
	public Grades decode(BsonReader reader, DecoderContext decoderContext) {
		Document document = documentCodec.decode(reader, decoderContext);
		System.out.println("document "+document);
		Grades grade = new Grades();

		grade.setId(document.getObjectId("_id"));

		grade.setStudentId(document.getInteger("student_id"));

		grade.setType(document.getString("type"));

		grade.setScore(document.getDouble("score"));
		
		return grade;
	}

	@Override
	public Grades generateIdIfAbsentFromDocument(Grades document) {
		return documentHasId(document) ? document.withNewObjectId() : document;
	}

	@Override
	public boolean documentHasId(Grades document) {
		return null == document.getId();
	}

	@Override
	public BsonValue getDocumentId(Grades document) {
		if (!documentHasId(document))
	    {
	        throw new IllegalStateException("The document does not contain an _id");
	    }
	 
	    return new BsonString(document.getId().toHexString());
	}
}