How to map binary data in a SpringData MongoDb Java bean?

Question

I have a bean that includes a Java object that is stored as binary data in Mongo DB. Introducing SpringData for mapping gave me the problem. So, the Bean code is:

@Document(collection = “cache”)
public class CacheBean {
    ... 
    private Object objectData;
    ...
}

The insertion code to Mongo Db is:

protected void setToMongo(String key, Object value){
    ByteArrayOutputStream b = new ByteArrayOutputStream();
    ObjectOutputStream o = new ObjectOutputStream(b);
    o.writeObject(value);
    CacheBean cacheBean = new CacheBean();
    cacheBean.setObjectData(getBytesForObject(o));
    mongoTemplate.save(cacheBean);
}
private byte[] getBytesForObject(Object o) throws IOException{
    ByteArrayOutputStream b = new ByteArrayOutputStream();
    ObjectOutputStream os = new ObjectOutputStream(b);
    os.writeObject(o);
    return b.toByteArray();
}

The extraction code is as follows:

Object resultObject = cacheBean.getObjectData();
org.bson.types.Binary result = (Binary) resultObject;
ByteArrayInputStream b = new ByteArrayInputStream(result.getData());
ObjectInputStream o = new ObjectInputStream(b);
return o.readObject();

I am getting the exception on the line

org.bson.types.Binary result = (Binary) resultObject:

java.lang.ClassCastException: [B cannot be cast to org.bson.types.Binary

Ori Dar · Accepted Answer · 2015-08-18 20:40:14Z

2

MongoDB implicitly store (I think) byte array as Bson BinData.

Note that you yourself set the objectData to a byte array:

cacheBean.setObjectData(getBytesForObject(o));

At that point private Object objectData; is of type byte[]

So there is nothing preventing you from declaring this in CacheBean:

private byte[] objectData;

And therefore...

ByteArrayInputStream b = new ByteArrayInputStream(cacheBean.getObjectData());
ObjectInputStream o = new ObjectInputStream(b);
return o.readObject();

For convenience, you may also want to store the object class as a field.

answered Aug 18, 2015 at 20:40

Ori Dar

19.1k5 gold badges61 silver badges76 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Alex Over a year ago

I actually used the same idea but I stored objectData as org.bson.types.Binary instead of byte[]

Collectives™ on Stack Overflow

How to map binary data in a SpringData MongoDb Java bean?

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related