如何使用Java从mysql获取数据

Question

I can't figure out how to get data from mySQL. This is my first attempt at using java to interact with mysql and its quiet confusing.

What I want this piece of code to do is go into my db find "table" then get the value of "column" where the persons' name = "name". Here's what I have

public boolean useProspawn(String column, String name ){
        //long time = System.currentTimeMillis()/1000;
        //long prevTime = 0;

        Calendar calendar = Calendar.getInstance();
        java.sql.Timestamp curTime = new java.sql.Timestamp(calendar.getTime().getTime());
        java.sql.Timestamp prevTime;
        long diff = 0;
        long duration = 0;
        try {
            PreparedStatement ps = DatabaseConnection.getConnection().prepareStatement("SELECT ? FROM accounts WHERE name = ?");
            ps.setString(1, column);
            ps.setString(2, name);
            ResultSet rs = ps.executeQuery();
            prevTime = rs.getTimestamp(column);
            ps.close();
            rs.close();

        } catch (SQLException e) {
            System.out.println("Error getting player's pro spawner times:"); //THIS IS THE ERROR THAT IS GETTING THROWN INTO THE CMD CONSOLE
            System.out.println(e);

            return false;
        }

       diff = curTime.getTime() - prevTime.getTime();
       duration = TimeUnit.MILLISECONDS.toHours(diff);
       if (duration < 24){
           return false;
       } else {
           try {
            String psStatement = "UPDATE accounts SET ?=? WHERE name=?";
            PreparedStatement ps = DatabaseConnection.getConnection().prepareStatement(psStatement);
            ps.setString(1, column);
            ps.setTimestamp(2, curTime);
            ps.setString(3,name);
            ResultSet rs = ps.executeQuery();
            ps.close();
            rs.close();
            return true; // can use spawner
        } catch (SQLException e) {
            System.out.println("Error updating player's pro spawner times..");
            return false;
        }

       }

    }

I noticed that I'm getting the error at my "try/catch" statement because the only thing that is getting output in to cmd is the "error getting..." statement. Any ideas whats going on?

Answer 1

One obvious error is that the way you use the ResultSet for the select is not correct. Before you can get the first row values, you must call next first on the ResultSet.

ResultSet rs = stmt.executeQuery(query);
while (rs.next()) {
}

JDBC Basic