Java Circuit

In this Post we are going to learn the most powerful Database Framework called JPA.

Here I am going to demonstrate CRUD(Create, Retrieve, Update and Delete) operations.

For this create the fallowing directory structure in Netbeans and create the fallowing JSPs and Servlets, and also generate the Entity Class.



index.jsp



view.jsp


addDept.jsp



Now the code for ViewAllServlet.java is given below, and prior to that inject Persistence into the servlet.

public class ViewAllServlet extends HttpServlet {
    @Resource
    private javax.transaction.UserTransaction utx;
   
    
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {

            Context ctx = (Context) new InitialContext().lookup("java:comp/env");
            utx.begin();
            EntityManager em = (EntityManager) ctx.lookup("persistence/LogicalName");
            //em.persist(object);
            Query q=em.createNamedQuery("Dept.findAll");
            List list=q.getResultList();
            utx.commit();

            request.setAttribute("list", list);
            RequestDispatcher view=request.getRequestDispatcher("/view.jsp");
            view.forward(request, response);
        } 
        catch(Exception e)
        {
            out.print(e.toString());
        }
        finally {
            out.close();
        }
    } 

Now, the code for DelDeptServlet.java is given below.

public class DelDeptServlet extends HttpServlet {
    @Resource
    private javax.transaction.UserTransaction utx;
   
    
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {


            String cmd=request.getParameter("cmd");

            if(cmd.equals("Submit"))
            {
                Short deptno=new Short(request.getParameter("deptno"));
                String dname=request.getParameter("dname");
                String loc=request.getParameter("loc");

                Dept dept=new Dept();
                dept.setDeptno(deptno);
                dept.setDname(dname);
                dept.setLoc(loc);

                Context ctx = (Context) new InitialContext().lookup("java:comp/env");
                utx.begin();
                EntityManager em = (EntityManager) ctx.lookup("persistence/LogicalName");
                em.persist(dept);
                utx.commit();

                RequestDispatcher view=request.getRequestDispatcher("/ViewAllServlet");
                view.forward(request, response);

            }


            if(cmd.equals("Delete"))
            {
                String deptno=request.getParameter("deptno");

                Context ctx = (Context) new InitialContext().lookup("java:comp/env");
                utx.begin();
                EntityManager em = (EntityManager) ctx.lookup("persistence/LogicalName");

                if(deptno!=null)
                {
                    Dept dept=em.find(Dept.class, new Short(deptno));
                    em.remove(dept);
                    utx.commit();
                    RequestDispatcher view=request.getRequestDispatcher("/ViewAllServlet");
                    view.forward(request, response);
                }


                String str[] =request.getParameterValues("del");

                if(str!=null)
                {
                    for(int i=0;i<<str.length;i++)
                    {
                        Dept dept=em.find(Dept.class, new Short(str[i]));
                        em.remove(dept);
                    }
                
                    utx.commit();

                    RequestDispatcher view=request.getRequestDispatcher("/ViewAllServlet");
                    view.forward(request, response);
                }
                else
                {
                    out.print("You Must Select atleast one Record to Delete");
                }
            }

            if(cmd.equals("Edit"))
            {
                Short deptno=new Short(request.getParameter("deptno"));
                Context ctx = (Context) new InitialContext().lookup("java:comp/env");
                utx.begin();
                EntityManager em = (EntityManager) ctx.lookup("persistence/LogicalName");
                Dept dept=em.find(Dept.class, deptno);
                utx.commit();

                request.setAttribute("dept", dept);
                RequestDispatcher view=request.getRequestDispatcher("/addDept.jsp");
                view.forward(request, response);

            }

            if(cmd.equals("Update"))
            {

                Short deptno=new Short(request.getParameter("deptno"));
                String dname=request.getParameter("dname");
                String loc=request.getParameter("loc");
                Context ctx = (Context) new InitialContext().lookup("java:comp/env");
                 utx.begin();
                EntityManager em = (EntityManager) ctx.lookup("persistence/LogicalName");
                Dept dept=em.find(Dept.class, deptno);
                dept.setDname(dname);
                dept.setLoc(loc);
                em.merge(dept);
                utx.commit();

                RequestDispatcher view=request.getRequestDispatcher("/ViewAllServlet");
                view.forward(request, response);
            }
            
        }

        catch(Exception e)
        {
            out.print(e.toString());
        }
        finally {
            out.close();
        }
    } 

When we compile the above program we will get the fallowing output.


That's it folks !!!

I will get back to you with some more interesting topics !!