JavaServer Faces

Accessing Application Data

The different parts of a Java web application need to be able access the same data objects. For instance, a product catalog object a listener creates at application start must be accessible by a servlet that processes a user query against the catalog, and the result of the query must be available to the JSP page that renders the response showing the result.

The Servlet API includes methods for managing this type of data as attributes of the objects representing the application, the user session, and the request, defined by these classes, respectively: javax.servlet.ServletContext, javax.servlet.http.HttpSession, and javax.servlet.ServletRequest.

All three classes contain these methods for managing the attributes:

public void setAttribute(String name, Object value);

public Object getAttribute(String name);

public void removeAttribute(String name);

In the product catalog example, the listener uses the setAttribute() method on the ServletContext to make the catalog available to the servlet, and the servlet uses the getAttribute( ) method to obtain it. To make the query result available to the JSP page, the servlet calls the setAttribute( ) method of either the HttpSession or the ServletRequest object (depending on how long the result must be available).

The JSP specification refers to these three attribute collections as different scopes: the application, session, and request scope. It also adds a collection of attributes available only to objects within ...