J2EE Design Patterns

Name

Data Transfer Hash

Goal

Reduce coupling between objects communicating via DTOs (Figure B-1).

Figure B-1. Data transfer hash classes

Participants

Business objects

Create hashes for sending data, or use values in received hashes.

Data transfer hash

Stores data for transport between layers as a set of values associated with well-known keys.

Presentation tier objects

Create hashes for sending data, or use values in received hashes.

Interactions

A presentation tier object requests data from the business tier. The business object reads the data, and inserts the values into a hash table with well-known keys for transport. The presentation tier object retrieves the data in the received hash by key. The presentation tier object modifies the received hash or creates a new one to transport data back to the business tier.

Notes

Data transfer hashes may be implemented as simple hash tables (or HashMaps). A more robust implementation uses a container object to hold the hash, as well as identifying information, type-safe data retrieval methods, and well-known keys.