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JPA uses a combination of annotation- and XML-based configuration. The XML file used for this purpose is persistence.xml,
which is located in the application's
META-INF directory. This file defines all the persistence units that are used by this application. Each persistence unit defines all
the entity classes that are mapped to a single database. The persistence.xml file for the Employee application is shown in
<persistence> <persistence-unit name="EmployeePU" transaction-type="RESOURCE_LOCAL"> <provider>oracle.toplink.essentials.PersistenceProvider</provider> <class>com.trial.Employee</class> <properties> <property name="toplink.jdbc.url" value="jdbc:mysql://localhost:3306/projects"/> <property name="toplink.jdbc.user" value="root"/> <property name="toplink.jdbc.driver" value="com.mysql.jdbc.Driver"/> <property name="toplink.jdbc.password" value="infosys"/> </properties> </persistence-unit> </persistence>
The persistence.xml file defines a persistence unit named
EmployeePU. The configuration for the corresponding database is also included in the persistence unit. An application can have multiple
persistence units that relate to different databases.
To summarize, JPA provides a standard POJO-based ORM solution for both Java SE and Java EE applications. It uses entity classes, entity managers, and persistence units to map and persist the domain objects and the tables in the database.
JPA should be used when you need a standard Java-based persistence solution. JPA supports inheritance and polymorphism, both features of object-oriented programming. The downside of JPA is that it requires a provider that implements it. These vendor-specific tools also provide certain other features that are not defined as part of the JPA specification. One such feature is support for caching, which is not clearly defined in JPA but is well supported by Hibernate, one of the most popular frameworks that implements JPA. Also, JPA is defined to work with relational databases only. If your persistence solution needs to be extended to other types of data stores, like XML databases, then JPA is not the answer to your persistence problem.
You've now examined three different persistence mechanisms and their operations. Each of these frameworks has its own pros and cons. Let's consider several parameters that will help you decide the best possible option among them for your requirements.
In the development of many applications, time is a major constraint, especially when team members need to be trained to use a particular framework. In such a scenario, iBATIS is the best option. It is the simplest of the three frameworks, because it only requires knowledge of SQL.
Traditional ORM solutions like Hibernate and JPA should be used to leverage complete object-relational mapping. Hibernate and JPA map Java objects directly to database tables, whereas iBATIS maps Java objects to the results of SQL queries. In some applications, the objects in the domain model are designed according to the business logic and might not completely map to the data model. In such a scenario, iBATIS is the right choice.
There has always been a demarcation between the people who are well versed in Java and those who are comfortable with SQL.
For a proficient Java programmer who wants to use a persistence framework without much interaction with SQL, Hibernate is
the best option, as it generates efficient SQL queries at runtime. However, if you want complete control over database querying
using stored procedures, then iBATIS is the recommended solution. JPA also supports SQL through the
createNativeQuery() method of the
iBATIS strongly supports SQL, while Hibernate and JPA use their own query languages (HQL and JPQL, respectively), which are similar to SQL.
An application must perform well in order to succeed. Hibernate improves performance by providing caching facilities that help with faster retrieval of data from the database. iBATIS uses SQL queries that can be fine-tuned for better performance. The performance of JPA depends on that of the vendor implementation. The choice is particular to each application.
Sometimes, you will need to change the relational database that your application uses. If you use Hibernate as your persistence solution, then this issue is easily resolved, as it uses a database dialect property in the configuration file. Porting from one database to another is simply a matter of changing the dialect property to the appropriate value. Hibernate uses this property as a guide to generate SQL code that is specific to the given database.
As previously mentioned, iBATIS requires you to write your own SQL code; thus, an iBATIS application's portability is dependent on that SQL. If the queries are written using portable SQL, then iBATIS is also portable across different relational databases. On the other hand, the portability of JPA depends on the vendor implementation that is being used. JPA is portable across different implementations, like Hibernate and TopLink Essentials. So, if no vendor-specific features are used by the application, portability becomes a trivial issue.
Hibernate is a clear winner in this aspect. There are many Hibernate-focused forums where members actively respond to queries. iBATIS and JPA are catching up slowly in this regard.
iBATIS supports .Net and Ruby on Rails. Hibernate provides a persistence solution for .Net in the form of NHibernate. JPA, being a Java-specific API, obviously does not support any non-Java platform.
This comparison is summarized in Table 1.
|Complete ORM solution||Average||Best||Best|
|Adaptability to data model changes||Good||Average||Average|
|Dependence on SQL||Good||Average||Average|
|Portability across different relational databases||Average||Best||N/A *|
|Portability to non-Java platforms||Best||Good||Not Supported|
|Community support and documentation||Average||Good||Good|
* The features supported by JPA are dependent on the persistence provider and the end result may vary accordingly.
iBATIS, Hibernate, and JPA are three different mechanisms for persisting data in a relational database. Each has its own advantages and limitations. iBATIS does not provide a complete ORM solution, and does not provide any direct mapping of objects and relational models. However, iBATIS provides you with complete control over queries. Hibernate provides a complete ORM solution, but offers you no control over the queries. Hibernate is very popular and a large and active community provides support for new users. JPA also provides a complete ORM solution, and provides support for object-oriented programming features like inheritance and polymorphism, but its performance depends on the persistence provider.
The choice of a particular persistence mechanism is a matter of weighing all of the features discussed in the comparison section of this article. For most developers the decision will be made based on whether you require complete control over SQL for your application, need to auto-generate SQL, or just want an easy-to-program complete ORM solution.
The authors would like to sincerely acknowledge S. V. Subrahmanya (SVS) for his valuable guidance and support.
S. Sangeetha works as a technical architect at the E-Commerce Research Labs at Infosys Technologies. She has close to 10 years of experience in design and development of Java and Java EE applications. She has co-authored a book on Java EE architecture and also has written articles for JavaWorld and Java.net.
K. L. Nitin works at the E-Commerce Research Labs at Infosys Technologies. He is involved in the design and development of Java EE applications using Hibernate and JPA, and has expertise on agile frameworks like Ruby on Rails.
Ananya S. works at the E-Commerce Research Labs at Infosys Technologies. She has been involved in the design, development, and deployment of Java EE applications using JPA and iBATIS. She also has experience in programming with Ruby and Ruby on Rails.
Mahalakshmi K. works at the E-Commerce Research Labs at Infosys Technologies. She has experience in Java EE technologies and database programming. She is involved in the design and development of Java EE applications using Hibernate and JPA. She has also worked on application development using the Ruby on Rails framework.
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