Question

I’m having a problem viewing my records from an arraylist in JSP page. Every time I load my JSP page automatically by javascript onload event, data is displayed but the process does not stop.

Categoria class:

package proyecto.modelo;

public class Categoria {

    private int idcategoria;

    public int getIdcategoria() {
        return idcategoria;
    }

    public void setIdcategoria(int idcategoria) {       
        this.idcategoria = idcategoria;
    }
}

BaseDAO class:

package proyecto.dao;

import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class BaseDAO {

    protected void cerrarConexion(Connection con) throws RuntimeException {
        try {
            if (con != null && !con.isClosed()) {
                con.close();
            }
        } catch (SQLException se) {
            System.err.println("Error: cerrarConexion: " + se);
        }
    }

    protected void cerrarResultSet(ResultSet rs) throws RuntimeException {
        try {
            if (rs != null) {
                rs.close();
            }
        } catch (SQLException se) {
            System.err.println("Error: cerrarResultSet: " + se);
        }
    }

    protected void cerrarStatement(PreparedStatement stmt)
            throws RuntimeException {
        try {
            if (stmt != null) {
                stmt.close();
            }
        } catch (SQLException se) {
            System.err.println("Error: cerrarStatement: " + se);
        }
    }

    protected void cerrarCallable(CallableStatement callstmt)
            throws RuntimeException {
        try {
            if (callstmt != null) {
                callstmt.close();
            }
        } catch (SQLException se) {
            System.err.println("Error: cerrarCallable: " + se);
        }
    }
}

CategoriaDAO class:

package proyecto.dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Collection;

import proyecto.excepcion.DAOExcepcion;
import proyecto.modelo.Categoria;
import proyecto.util.ConexionBD;

public class CategoriaDAO extends BaseDAO {

    public Collection<Categoria> listarIdCat() throws DAOExcepcion{

        Collection<Categoria> = new ArrayList<Categoria>();
        String query = "SELECT id_categoria from categoria ";
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;

        try {
            con=ConexionBD.obtenerConexionDirecta();
            stmt=con.prepareStatement(query);
            rs=stmt.executeQuery();

            while(rs.next()) {
                Categoria vo=new Categoria();
                vo.setIdcategoria(rs.getInt("id_categoria"));
                c.add(vo);
            }

        } catch (SQLException e) {
            System.err.println(e.getMessage());
            throw new DAOExcepcion(e.getMessage());
        } finally {
            this.cerrarStatement(stmt);
            this.cerrarResultSet(rs);
            this.cerrarConexion(con);
        }

        return c;
    }

}

CategoriaNegocio class:

package proyecto.negocio;

import java.util.Collection;
import java.util.List;

import proyecto.dao.CategoriaDAO;
import proyecto.excepcion.DAOExcepcion;
import proyecto.modelo.Categoria;

public class CategoriaNegocio {

    public Collection<Categoria> listarIdCat() throws DAOExcepcion {
        CategoriaDAO dao = new CategoriaDAO();
        Collection<Categoria> lista = dao.listarIdCat();
        return lista;
    }

}

Servlets doPost() method:

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    CategoriaNegocio negocio = new CategoriaNegocio();

    try {
        Collection<Categoria> lista = negocio.listarIdCat();
        request.setAttribute("IDCATEGORIA", lista);
    } catch (DAOExcepcion e) {
        System.out.println(e.getMessage());
    }

    RequestDispatcher rd = request.getRequestDispatcher("listar_idcat.jsp");
    rd.forward(request, response);
}

JSP:

<%@page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"   %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<html>
    <head>
        <script type="text/javascript">
            window.onload = function() {
                document.formulario.submit()
            };
            document.close();
        </script>
    </head>
    <body>
        <form action="ListarIdCatServlet" method="post" name="formulario"></form>
        <table>
            <c:forEach items="${IDCATEGORIA}" var="c">
                <tr>
                    <td>${c.idcategoria}</td>
                </tr>
            </c:forEach>
        </table>
    </body>
</html>

Answer 1

You seem to want to invoke a servlet on a GET request. You’re approaching this the wrong way. You should not be submitting a POST form on load of the page. You should be performing the job in the doGet() method of the servlet and be invoking it directly.

You need to make the following changes:

1. Change URL pattern of servlet to /listar_idcat.

2. Rename doPost method of servlet to doGet.

3. Move listar_idcat.jsp file into /WEB-INF folder (this prevents direct access by endusers).

4. Change getRequestDispatcher("listar_idcat.jsp"); call in servlet to getRequestDispatcher("/WEB-INF/listar_idcat.jsp");.

5. Remove the whole <script> from JSP.

6. Remove the whole <form> from JSP.

Now, open the JSP by http://localhost:8080/context/listar_idcat instead (yes, without the .jsp extension! it’ll invoke the servlet’s doGet() directly).

See also:

• Our Servlets wiki page – Hello World #2.