driver-legacy/src/main/com/mongodb/DB.java
public Set<String> getCollectionNames() {
        List<String> collectionNames =
                new MongoIterableImpl<DBObject>(null, executor, ReadConcern.DEFAULT, primary(),
                        mongo.getMongoClientOptions().getRetryReads()) {
                    @Override
                    public ReadOperation<BatchCursor<DBObject>> asReadOperation() {
                        return new ListCollectionsOperation<DBObject>(name, commandCodec)
                                .nameOnly(true);
                    }
                }.map(new Function<DBObject, String>() {
                            @Override
                            public String apply(final DBObject result) {
                                return (String) result.get("name");
                            }
                        }).into(new ArrayList<String>());
        Collections.sort(collectionNames);
        return new LinkedHashSet<String>(collectionNames);
    }
public Set<String> getCollectionNames() {
        List<String> collectionNames =
                new MongoIterableImpl<DBObject>(null, executor, ReadConcern.DEFAULT, primary(),
                        mongo.getMongoClientOptions().getRetryReads()) {
                    @Override
                    public ReadOperation<BatchCursor<DBObject>> asReadOperation() {
                        return new ListCollectionsOperation<DBObject>(name, commandCodec)
                                .nameOnly(true);
                    }
                }.map(new Function<DBObject, String>() {
                            @Override
                            public String apply(final DBObject result) {
                                return (String) result.get("name");
                            }
                        }).into(new ArrayList<String>());
        Collections.sort(collectionNames);
        return new LinkedHashSet<String>(collectionNames);
    }
Returns a set containing the names of all collections in this database.

@return the names of collections in this database
@throws MongoException if the operation failed
@mongodb.driver.manual reference/method/db.getCollectionNames/ getCollectionNames()