We currently have a Stateful bean that is injected into a Servlet. The problem is that sometimes we get a Caused by: javax.ejb.ConcurrentAccessException: SessionBean is executing another request. [session-key: 7d90c02200a81f-752fe1cd-1] when executing a method on the stateful bean.
public class NewServlet extends HttpServlet {
@EJB
private ReportLocal reportBean;
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
try {
String[] parameters = fetchParameters(request);
out.write(reportBean.constructReport(parameters));
} finally {
out.close();
}
}
}
In the above code, constructReport will check if it needs to open a new connection to the database specified in the Report after which a Report in HTML is constructed from a query which is built from the parameters specified.
The reason why we chose to use a stateful bean over a stateless bean was because we need to open a database connection to an unknown database and perform queries on it. With a stateless bean it seems terribly inefficient to repeatedly open and close database connections with each injected instance of the bean.
This is not what stateful session beans (SFSB) are intended to be used for. They are designed to hold conversation state, and are to be bound to the user's http session to hold that state, like a heavyweight alternative to storing state in the session directly.
If you want to hold things like database connections, then there are better ways to go about it.
Best option is to use a connection pool. You should always use a connection pool, and if you're running inside an application server (which, if you're using EJBs, then you are), then you can easily use your appserver's datasource configuration to create a connection pool, and use that inside your stateless session bean (SLSB).