Criando Servlet de Controle exer. 9.6 Caelum Web

package br.com.caelum.mvc.logica;


import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public interface Logica {

	String executa(HttpServletRequest req, HttpServletResponse res) throws Exception;
	
}

package br.com.caelum.mvc.logica;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class PrimeiraLogica implements Logica {

	@Override
	public String executa(HttpServletRequest req, HttpServletResponse res) throws Exception {

		System.out.println("Executando a logica...");

		System.out.println("Retornando o nome da pagina jsp...");

		return "primeira-logica.jsp";
	}

}

package br.com.caelum.mvc.servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import br.com.caelum.mvc.logica.Logica;

@WebServlet("/mvc")
public class ControllerServlet extends HttpServlet {

	@Override
	protected void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {

		String parametro = req.getParameter("logica");
		String nomeDaClasse = "br.com.caelum.mvc.logica" + parametro;

		try {
			Class classe = Class.forName(nomeDaClasse);

			Logica logica = (Logica) classe.newInstance();
			String pagina = logica.executa(req, res);

			req.getRequestDispatcher(pagina).forward(req, res);
		} catch (Exception e) {
			throw new ServletException("A logica de negocios causou uma exceção", e);

		}
	}
}