Java - Using a prepared statement in two methods

Question

I'm kinda starting with connections and all that but i wanted to save a prject to a database I created the connection everything is working fine until i execute the preparedStatement. In the first method it works fine but then (in that same method) I call another method and use the same preparedStatement now with to a different table. But i get a BatchUpdateException. Here is some of the code:

    public void openConnection() throws SQLException {

    DriverManager.registerDriver
       (new oracle.jdbc.OracleDriver());      

    connection = DriverManager.getConnection(jdbcUrl, username, password);
    connection.setAutoCommit(false);
    }

    public boolean addProject(Project proj)
        throws SQLException {

    stmt = connection.prepareStatement("insert into PROJECT (p_name, description) values (?, ?)");

    stmt.setString(1, proj.getName());
    stmt.setString(2, proj.getDescription());
    stmt.addBatch();

    try {
        stmt.executeBatch();
    } catch (BatchUpdateException e) {
        System.out.println("plop");
        return false;
    }

    boolean flag1 = addSimulationList(proj);

    boolean flag2 = addRoadNetwork(proj);

    boolean flag3 = addVehicleList(proj);

    if (flag1 == false || flag2 == false || flag3 == false) {
        return false;
    }

    connection.commit();
    stmt.close();

    return true;

}

/**
 * Adds a specific simulation to the table "Simulations".
 *
 * @param proj Project
 */
public boolean addSimulationList(Project proj)
        throws SQLException {

    stmt = connection.prepareStatement("insert into SIMULATION (p_name, s_code, description) values (?, ?, ?)");

    boolean flag1 = true, flag2 = true;

    for (Simulation s : proj.getSimList()) {

        stmt.setString(1, proj.getName());
        stmt.setString(2, s.getSimID());
        stmt.setString(3, s.getDescription());

        stmt.addBatch();

    }

    int[] totalInserted = new int[proj.getSimList().size()];

    try {
        totalInserted = stmt.executeBatch(); //it triggers here
    } catch (BatchUpdateException e) {
        totalInserted = e.getUpdateCounts();
        return false;
    }

Answer 1

Your original prepared statement is open when you redirect the variable to a new prepared statement. Your statement.close() isn't closing the obvious instance. This is perhaps poor programming style.

Use a local PreparedStatement variable per method. Don't use a global variable like this. It's just going to get you into trouble.

Try switching to better coding practices and see if your issue disappears.