JPA or JDBC, how are they different?

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 , 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 encountered was that the PersistenceUnit attribute would only be recognized 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 :(

In layman's terms:

• JDBC is a standard for Database Access
• JPA is a standard for ORM

JDBC is a standard for connecting to a DB directly and running SQL against it - e.g SELECT * FROM USERS, etc. Data sets can be returned which you can handle in your app, and you can do all the usual things like INSERT, DELETE, run stored procedures, etc. It is one of the underlying technologies behind most Java database access (including JPA providers).

One of the issues with traditional JDBC apps is that you can often have some crappy code where lots of mapping between data sets 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 and 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 it's 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 from and to the DB.

Main difference between JPA and JDBC is level of abstraction.

JDBC is a low level standard for interaction with databases. JPA is higher level standard for the same purpose. JPA allows you to use an object model in your application which can make your life much easier. JDBC allows you to do more things with the Database directly, but it requires more attention. Some tasks can not be solved efficiently using JPA, but may be solved more efficiently with JDBC.

JDBC is a much lower-level (and older) specification than JPA. In it's bare essentials, JDBC is an API for interacting with a database using pure SQL - sending queries and retrieving results. It has no notion of objects or hierarchies. When using JDBC, it's up to you to translate a result set (essentially a row/column matrix of values from one or more database tables, returned by your SQL query) into Java objects.

Now, to understand and use JDBC it's essential that you have some understanding and working knowledge of SQL. With that also comes a required insight into what a relational database is, how you work with it and concepts such as tables, columns, keys and relationships. Unless you have at least a basic understanding of databases, SQL and data modelling you will not be able to make much use of JDBC since it's really only a thin abstraction on top of these things.

JDBC is the predecessor of JPA.

JDBC is a bridge between the Java world and the databases world. In JDBC you need to expose all dirty details needed for CRUD operations, such as table names, column names, while in JPA (which is using JDBC underneath), you also specify those details of database metadata, but with the use of Java annotations.

So JPA creates update queries for you and manages the entities that you looked up or created/updated (it does more as well).

If you want to do JPA without a Java EE container, then Spring and its libraries may be used with the very same Java annotations.