I am learning Java EE and I downloaded the eclipse with glassfish for the same. I saw some examples and also read the Oracle docs to know all about Java EE 5. Connecting to a database was very simple. I opened a dynamic web project, created a session EJB and I used EntityManager and with the get methods could access the stored data table.
For my next project I had create a simple class and then access some DB table. The very first problem I encuntered was, that the PersistenceUnit attribute would only be recognised by EJB,Servlet etc and not a simple java class. So then I could not use the EntityManager way(or can I?)
I was asked to go via the "JDBC" way. The very first problem I encountered was to get the connection to the DB. It seems all this must be hardcoded. I had a persistence.xml with which I could easily configure the data base connection. Even setting up a driver for the DB was easy. Also there no get/set methods in the JDBC for accessing table entities.
How do I understand JPA and persistence in relation to JDBC? What was JPA thought for? Why is there set/get methods? Can someone throw some light on the essence of these two and what are the pros/cons without "jargons"?? Please also suggest some links. A simple google search for JPA and JDBC differences led me to some sites full of "terminology" I couldn't follow :(
JDBCis a standard for Database Access
JPAis a standard for
JDBC is a standard for connecting to a DB directly and running SQL against it - e.g SELECT * FROM USERS, etc. Datasets can be returned which you can handle in your app, and you can do all the usual things like INSERTS, DELETES, run stored procedures, etc. It is one of the underlying technologies behind most java database access (including
One of the issues with traditional
JDBC apps is that you can often have some crappy code where lots of mapping between datasets and objects occur, logic is mixed in with SQL, etc.
JPA is a standard for Object Relational Mapping. This is a technology which allows you to map between objects in code and database tables. This can "hide" the SQL from the developer so that all they deal with are java classes, and the provider allows you to save them and load them magically. Mostly, XML mapping files or annotations on getters, setters can be used to tell the JPA provider which fields on your object map to which fields in the DB. The most famous JPA provider is Hibernate, so is a good place to start for concrete examples.
Other examples include OpenJPA, toplink, etc.
Under the hood, Hibernate and most other providers for JPA write SQL and use JDBC to read and write to the DB.