问题:

I was wondering what the Java driver's equivalent to the Mongo JavaScript shell's Object.bsonsize( doc ) method? For example, what is the Java code to perform the following:

bobk-mbp:~ bobk$ mongo
MongoDB shell version: 2.0.4
connecting to: test
PRIMARY> use devices;
switched to db devices
PRIMARY> Object.bsonsize( db.profiles.findOne( { _id: "REK_0001" } ) );
186
PRIMARY> Object.bsonsize( db.profiles.findOne( { _id: "REK_0002" } ) );
218
PRIMARY>

How do I perform this same basic use case with the MongoDB Java Driver. Its not obvious through the JavaDocs.

回答1:

There's nothing quite as clean as what's available in the shell, but this will work:

DBObject obj = coll.findOne();
int bsonSize = DefaultDBEncoder.FACTORY.create().
        writeObject(new BasicOutputBuffer(), obj));

回答2:

You can use BasicBSONEncoder:

DBObject obj = coll.findOne();
int bsonSize = new BasicBSONEncoder().encode(obj).length;

回答3:

What about:

        CommandResult result = db.doEval("Object.bsonsize(db.profiles.findOne({ _id: "REK_0001" }))");
        double bsonSize = (Double) result.get("retval");

It's double instead of int.

doEval is part of the MongoDB Java Driver since the first version.