MongoDB java driver. The custom builder for update operations.

DBCollection collection = new Mongo("localhost", 27017)
        .getDB("test").getCollection("users");
DBObject criteria = new QueryBuilder().put("name")
        .is("Perry").and("age").greaterThan(20).get();
DBObject doc = collection.findOne(criteria);

/**
 * The utility for creating update queries.
 */
public class Builder {

    /**
     * The update query.
     */
    private final DBObject query;

    /**
     * Initializes the update builder.
     */
    public Builder() {
        query = new BasicDBObject();
    }

    /**
     * Sets the new value for the field.
     *
     * @param key    field name
     * @param object value to set
     * @return Builder instance
     */
    public Builder set(final String key,
                       final Object object) {
        addToQuery(Operators.SET, key, object);

        return this;
    }

    /**
     * Increments the field by a specified value.
     *
     * @param key   field name
     * @param value number value
     * @return Builder instance
     */
    public Builder inc(final String key,
                       final int value) {
        addToQuery(Operators.INC, key, value);

        return this;
    }

    /**
     * Deletes the field.
     *
     * @param key field name
     * @return Builder instance
     */
    public Builder unset(final String key) {
        addToQuery(Operators.UNSET, key, 1);

        return this;
    }

    /**
     * Checks whether the builder is empty.
     *
     * @return true if the builder is empty, false otherwise
     */
    public boolean isEmpty() {
        return query.keySet().isEmpty();
    }

    /**
     * Creates the DBObject-based query to be used for update operations.
     *
     * @return the query instance
     */
    public DBObject get() {
        return query;
    }

    /**
     * Adds the operation to the query.
     *
     * @param operator update operator
     * @param key      param to update
     * @param object   value to set
     */
    private void addToQuery(final String operator,
                            final String key,
                            final Object object) {
        final BasicDBObject subQuery = query.get(operator) != null ?
                (BasicDBObject) query.get(operator) : new BasicDBObject();

        query.put(operator, subQuery.append(key, object));
    }
}

/**
 * MongoDB keywords for update operations.
 */
public class Operators {

    public final static String SET = "$set";

    public final static String INC = "$inc";

    public final static String UNSET = "$unset";
}

DBCollection collection = new Mongo("localhost", 27017)
        .getDB("test").getCollection("users");
DBObject criteria = new QueryBuilder().put("name")
        .is("Perry").get();
DBObject update = new Builder().inc("age", 1).get();
collection.update(criteria, update);