Include BD data in Java

Question

I’m following a distance course, only I’m having trouble including the record. It does not include, but it also does not present any error, and by the examples of the teacher I followed, it did not work. I’ve also seen several video lessons on the Internet and handouts, but still not included in the comic.

NOTE: I already tested the connection with the BD and everything is OK.

Class Connection to the BD:

    public Statement stm; // Prepara e realiza pesquisas no BD.
    public ResultSet rs; // Armazena o resultado de uma pesquisa passada para o STM.
    private String driver = "com.mysql.jdbc.Driver"; // Identificar o BD.
    private String caminho = "jdbc:mysql://127.0.0.1/alunos"; // Seta o local do BD.
    private String usuario = "root";
    private String senha = "";
    public Connection conn; // Realiza a conexao com o BD.


    public void conexao(){ // Metodo que realizar conexao com o BD.
        try {
            System.setProperty("jdbc.Drivers", driver); // Seta a propriedade do driverde conexao
            conn = DriverManager.getConnection(caminho, usuario, senha); // Realizao conexao com o BD.
            System.out.println("Conectado com Sucesso!");
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public void desconecta(){ // Metodo para fechar conexao BD.
        try {
            conn.close(); // Fecha conexao.
        } catch (SQLException e) {
            e.printStackTrace();
        }

Class receiving the methods:

public class Alunos {

    ConexaoAluno conecta = new ConexaoAluno();  // Variavel global.

    public void incluir(){

        conecta.conexao();

        try {
            PreparedStatement pst = conecta.conn.prepareStatement("insert into alunos (endereco, cep, cidade, estado, pais) values(?,?,?,?,?)");
            pst.setString(1, "Av. Mantiqueira");
            pst.setString(2, "74565-410");
            pst.setString(3, "Goiania");
            pst.setString(4, "GO");
            pst.setString(5, "Brasil");
            pst.executeUpdate();
            System.out.print("Inserido com sucesso!");
        } catch (SQLException e) {
            e.printStackTrace();
        }       

Class calling methods and executing:

public class TestaAluno {

    public static void main(String[] args) {

        Alunos al = new Alunos();

        al.incluir();

    }

Answer 1

You are not managing the connection and the PreparedStatement in appropriate ways, and is dropping them open. Use the syntax Try-with-Resources Java 7+ to solve this in the simplest way.

Do so:

public class ConexaoAluno {
    private static final String driver = "com.mysql.jdbc.Driver";
    private static final String caminho = "jdbc:mysql://127.0.0.1/alunos";
    private static final String usuario = "root";
    private static final String senha = "";

    static {
        System.setProperty("jdbc.Drivers", driver);
        try {
            Class.forName(driver);
        } catch (ClassNotFoundException e) {
            throw new ExceptionInInitializerError("Erro fatal. Não foi possível achar o driver do MySQL", e);
        }
    }

    public Connection conexao() throws SQLException {
        return DriverManager.getConnection(caminho, usuario, senha);
    }
}

public class Alunos {

    private static final String INCLUIR_SQL = "INSERT INTO alunos (endereco, cep, cidade, estado, pais) VALUES (?, ?, ?, ?, ?)";

    private final ConexaoAluno conecta;

    public Alunos() {
        conecta = new ConexaoAluno();
    }

    public void incluir() {
        try (Connection conn = conecta.conexao(),
            PreparedStatement pst = conn.prepareStatement(INCLUIR_SQL))
        {
            pst.setString(1, "Av. Mantiqueira");
            pst.setString(2, "74565-410");
            pst.setString(3, "Goiania");
            pst.setString(4, "GO");
            pst.setString(5, "Brasil");
            pst.executeUpdate();
            System.out.print("Inserido com sucesso!");
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

public class TestaAluno {
    public static void main(String[] args) {
        Alunos al = new Alunos();
        al.incluir();
    }
}

And another thing, you may have seen that maintaining public attributes is bad programming practice, isn’t it? So please don’t do this.

Ah yes, and make sure that the Mysql Connector JAR is on your classpath.