Explore the concepts of Data Access Objects (DAOs), Data Transfer Objects (DTOs), and Client/Server Architecture in application development. Learn about the roles of DTOs in moving data, managing transactions, and best practices for handling connections in DAOs. Avoid common pitfalls in Service or Façade classes by considering key questions related to DAO methods and SQL exceptions.
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Data Transfer Objects (DTOs) Data-only (plus accessors) classes used to move (or transfer ) data from point A to point B in an application Moving data into and out of the Data Persistence subsystem Create, Update, Delete: DTOs passed into DAOs Read: DTOs passed out of DAOs Transferring data between client and server (typically over a network) Web API parameters Web API results 5
Transactions See TransactionManager.java example Service or fa ade does the following: Calls begin() Calls each DAO method to be included in the transaction Calls end(Boolean) (from within a finally block) (pass false if any of the DAOs threw an SQLException) Each DAO in the transaction calls getConnection()to use the same connection (and therefore be part of the same transaction) 11
Questions to Consider Who calls the DAO methods? Should DAO methods throw SQL Exceptions? Why or why not? How do DAOs get connections? Why should this matter? What problem(s) do you see with the Service or Fa ade classes calling the TransactionManger? How can we avoid them? 12
