Implementation: What Is JPA And JPA?

The basic Java framework to access the database is JDBC. Unfortunately, with JDBC, a lot of hand work is needed to convert a database query result into Java classes.

JPA allows us to work with Java classes as it provides a transparent layer to each database specific details; JPA will do the hard work of mapping table to class structure and semantics for the developer.

An easy definition to JPA is: “A group of specifications (a lot of texts, regularizations and Java Interfaces) to define how a JPA implementation should behave”. There are many JPA implementations available both free and paid, e.g. Hibernate, OpenJPA, EclipseLink and the “new born” Batoo etc.

Most JPA implementations are free to add extra codes, annotations that are not present in the JPA specification, but must conform to the JPA specification scemantics.

The main JPA feature to address application portability is the ability to map database tables into the classes. In the following sections we will demonstrate how it is possible to map the column of a table into a Java class field regardless of the names of both the batabase column and Java class field.

JPA created a database language named JPQL to perform database queries. The advantage of JPQL is that the query can be executed in all databases.

SELECT id, name, color, age, doors FROM Car

The query above could be translated to the JPQL below:

SELECT c FROM Car c

Notice that the result of the query above is “c”, that means, a car object and not the fields/values found in the database table. JPA will create the object automatically.

JPA will be responsible to translate the JPQL query to the database native query; the developer will not need to worry about which is the required sql database syntax.