Why does my DriverManager return null pointer?

Question

Why does my DriverManager return null pointer?

Navigation

#1 by (1 votes)

3

PostgreSQL 9.4

I run my class Noticias() .

Within method public static void main() of class Noticias() the call is made from a getConexao() method;

When I run pagecontroller?=p=noticias in the browser it returns me java.lang.NullPointerException .

When I run the Noticias() class in Eclipse it does not return a pointer null and makes connection to the database without any error.

Note: Inside the WebContent / WEB-INF / lib / directory I'm with lib postgresql-9.4-1201.jdbc4.jar but anyway when I use my class Noticias() browser is not connected to the database, my Tomcat server is running through the Eclipse IDE.

public class PageController extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public PageController() {
       super();
    }

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out.println("Chamou o metodo GET");

    String pagina = request.getParameter("p");


    if (pagina.equals("noticias")){
        Noticias noticias = new Noticias();
        List<Noticias> lista = noticias.getNoticias();
        request.setAttribute("noticias", lista);
        RequestDispatcher saida = request.getRequestDispatcher("noticias.jsp");
        saida.forward(request, response);
    }

}

Follow class Noticias() :

public class Noticias{

int grid;
String topico;
String conteudo;
int usuario;
Date data;

public Noticias(){
}

public static void main(String[] args) {
    List<Noticias> noticias = getNoticias();
}

public static List<Noticias> getNoticias(){
    List<Noticias> noticia_list = new ArrayList<Noticias>();
    String sql = "SELECT * from NOTICIAS";

    Connection conexao = null;

    try {
        conexao = DriverManager.getConnection("jdbc:postgresql://localhost:5432/base", "postgres", "postgres");
        System.out.print("Conexao com o banco de dados efetuada com sucesso!");

    } catch (SQLException ex) {
        Logger.getLogger(DB.class.getName()).log(Level.SEVERE, null, ex);
        System.out.println("Erro durante a conexao com o banco de dados!");
    }

    PreparedStatement prepared_sql = null;

    try {
        prepared_sql = conexao.prepareStatement(sql);
    } catch (SQLException e) {
        e.printStackTrace();
    }

    try {
        ResultSet result = prepared_sql.executeQuery();

        while(result.next()){
            Noticias noticia = new Noticias();
            noticia.setGrid(result.getInt("grid"));
            noticia.setTopico(result.getString("topico"));
            noticia.setConteudo(result.getString("conteudo"));
            noticia.setUsuario(result.getInt("usuario"));
            noticia.setData(result.getDate("data"));

            noticia_list.add(noticia);
        }

    } catch (SQLException e) {
        e.printStackTrace();
    }

    return noticia_list;
}

java postgresql jdbc servlet

asked by anonymous 20.06.2015 / 19:44

1 answer

Return to the Start Menu when pressing ESC with JavaFx How to override the Iterator remove () method?

score 1 · Accepted Answer

Verifies that the driver's .jar is in the /WEB-INF/lib directory.

~~Are you doing pagecontroller?=p=noticias same?~~

It has 2 equals in this parameter, which completely zeros. Make

pagecontroller?p=noticias

The nullpointer seems to me to be that it does not find getParameter("p") ai .equals resulting in error .

UPDATE

Add Class.forName("org.postgresql.Driver"); before your connection:

try {
    Class.forName("org.postgresql.Driver"); 
    conexao = DriverManager.getConnection("jdbc:postgresql://localhost:5432/base", "postgres", "postgres");
    System.out.print("Conexao com o banco de dados efetuada com sucesso!");

} catch (SQLException ex) {
    Logger.getLogger(DB.class.getName()).log(Level.SEVERE, null, ex);
    System.out.println("Erro durante a conexao com o banco de dados!");
}