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Struts Recipes: Hibernate and Struts

Add the power of Hibernate to your Struts application

By George Franciscus and Danilo Gurovich, JavaWorld.com, 01/24/05

Persistence is a fundamental piece of an application. Obviously, without persistence all work would be lost. However, persistence means different things to different people. The length of time something must be persisted is a fundamental qualifier in choosing a persistence storage medium. For example, the HTTP session may be suitable when the life of a piece of data is limited to the user's session. In contrast, persistence over several sessions, or several users, requires a database. The volume of data is another important qualifier. For example, best practices suggest large amounts of data should not be stored in an HTTP session. In those circumstances, you need to consider a database. In this recipe we target persistence in a database.

The type of database you choose has an important influence on your architecture and design. As object-oriented developers, we tend to represent data as an interconnected web of objects as a means to describe the business problem at hand—this is often called a domain model. However, the most common storage medium is based on a relational paradigm. Unless our object model mirrors a relational structure, the in-memory representation of our data is at odds with the means to persist it. This problem is called the mismatch paradigm. One of the most popular tools to address the mismatch problem is a category of tools called object-relational mappers. An object-relational mapper is software used to transform an object view of the data into a relational one, and provide persistence services, such as create, read, update, and delete (CRUD). Many good papers have been written on object-relational mappers, but in essence, they all speak to the Data Mapper pattern. One of the most popular object-relational mappers is the open source Hibernate project.

In this recipe, we show you how to employ Hibernate in a Struts application. In addition, we will show you how to create a Struts plug-in to give your Hibernate-powered Struts applications a performance boost.

Recipe

In this recipe, we use an example to illustrate everything you need to do to use Hibernate in a Struts application. We create an application to retrieve and display elements from the chemical periodic table. The application offers the user a search page to look for an element by element symbol. The application responds by searching the database for an element matching the symbol name and returns information about the element.

We'll start by showing you how to get the Hypersonic database server up and running. With the database server started, we create the table and data required to exercise the application. Once the database is ready to go, we'll create all the Hibernate artifacts required to execute this application by using the Hypersonic database server. The next step is to respond to search requests by calling upon Hibernate to handle database access from inside our Action. Because creating Hibernate factory objects is expensive, we'll create a Struts plug-in to create the factory and store it in context.