Erro: java.lang.NullPointerException

Programação
,
#1

Alguém pode me explicar o motivo desse erro? E o que eu fiz de errado pra tá dando isso?

Clinica:

package modelo;

public class Clinica {

private int id;
private String cnpj;
private String nome;

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getCnpj() {
    return cnpj;
}

public void setCnpj(String cnpj) {
    this.cnpj = cnpj;
}

public String getNome() {
    return nome;
}

public void setNome(String nome) {
    this.nome = nome;
}

}

ClinicaDAO:

package modelo;

import java.sql.PreparedStatement;

public class ClinicaDAO extends DataBaseDAO {

public void inserir(Clinica clinica) throws Exception {
    this.conectar();
    String sql = "INSERT INTO clinica (cnpj, nome) VALUES (?, ?)";
    PreparedStatement pstm = conn.prepareStatement(sql);
    pstm.setString(1, clinica.getCnpj());
    pstm.setString(2, clinica.getNome());
    pstm.execute();
    this.desconectar();
}

}

GerenciarClinica:

package controle;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import modelo.Clinica;
import modelo.ClinicaDAO;

public class GerenciarClinica extends HttpServlet {

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    try (PrintWriter out = response.getWriter()) {
        /* TODO output your page here. You may use following sample code. */
        out.println("<!DOCTYPE html>");
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Servlet GerenciarClinica</title>");            
        out.println("</head>");
        out.println("<body>");

/* ============================================================================= */
request.setCharacterEncoding(“UTF-8”);

        int id;
        String op = request.getParameter("op");
        String cnpj = request.getParameter("cnpj");
        String nome = request.getParameter("nome");
        
        try {
            Clinica clinica = new Clinica();
            if(op.equals("alterar") || op.equals("excluir")) {
                id = Integer.parseInt(request.getParameter("id"));
                clinica.setId(id);
            }
            clinica.setCnpj(cnpj);
            clinica.setNome(nome);
            
            ClinicaDAO clinicaDAO = new ClinicaDAO();
            switch (op) {
                case "inserir": {
                    if (cnpj.isEmpty() || cnpj.equals("")) {
                        out.println("<script type='text/javascript'>");
                        out.println("alert('O campo 'CNPJ' deve ser preenchido!');");
                        out.println("hitory.back();");
                        out.println("</script>");
                    } else if (nome.isEmpty() || nome.equals("")) {
                        out.println("<script type='text/javascript'>");
                        out.println("alert('O campo 'NOME' deve ser preenchido!');");
                        out.println("hitory.back();");
                        out.println("</script>");
                    } else {
                        clinicaDAO.inserir(clinica);
                    }
                }
                break;
            }
            
        } catch (Exception e) {
            out.println("<script type='text/javascript'>");
            out.println("alert('Erro: " + e + "');");
            out.println("hitory.back();");
            out.println("</script>");
        }

/* ============================================================================= */
out.println("");
out.println("");
}
}

// <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
/**
 * Handles the HTTP <code>GET</code> method.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

/**
 * Handles the HTTP <code>POST</code> method.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

/**
 * Returns a short description of the servlet.
 *
 * @return a String containing servlet description
 */
@Override
public String getServletInfo() {
    return "Short description";
}// </editor-fold>

}

Erro:

image.jpg1024×768 88.7 KB

#2

Qual é a linha que acontece o erro? Cadê a stack trace?

Ali aonde tem:

catch (Exception e) {
    out.println("<script type='text/javascript'>");
    out.println("alert('Erro: " + e + "');");
    out.println("hitory.back();");
    out.println("</script>");
}

Você está engolindo a exception e jogando pro cliente. Assim não tem como descobrir onde está o erro sem debugar.