无法使用 html 和连接池从数据库中获取数据

Question

我是 java 新手，从 MySQL 获取数据时遇到问题。

我可以建立连接，他们正在等待但无法从数据库中获取数据

Answer 1

要从 Sql Db 中检索数据，您首先需要打开一个连接。创建一个如下所示的类：

 public static final String URL = "jdbc:mysql://url";
    public static final String USER = "user";
    public static final String PASS = "pass";
    public ConnectionFactory()

 {
        }



        public  Connection getConnection() {
            try {
                DriverManager.registerDriver(new com.mysql.jdbc.Driver());
                return DriverManager.getConnection(URL, USER, PASS);
            } catch (SQLException ex) {
                throw new RuntimeException("Error connecting to the database", ex);
            }}

然后是另一个类来控制与数据库的连接并获取您可能需要的任何信息。在您的情况下，它是 getCompanyById：

    public class DbController implements Serializable{

        private ConnectionFactory connectionFactory = new ConnectionFactory();

        public boolean getCompanyById(int id){
            boolean result = false;
            try {
                Statement stmt = null;
                //connect to database
                Connection conn = connectionFactory.getConnection();
                System.out.println("Connected database successfully...");
                stmt = conn.createStatement();
// cast results to Resultset
                Resultset resultset = stmt.executeQuery(""SELECT * FROM COMPANY WHERE ID ="+Id+"");

//Iterate through the results creating a new Company object for each set of results and then add them to an ArrayList to filter later on.
          while (resultSet.next()) {
                Company company = new Company();
                company.setId(resultSet.getInt("id"));
                company.setCap(resultSet.getDouble("cap"));
                company.setDescription(resultSet.getString("description"));
                company.setMinimum(resultSet.getDouble("minimum"));
                 companyList.add(margin);
}

                conn.close();
                System.out.println("Disconnected from database...");
                result = true;
            }
            catch (SQLException exception){
                System.out.println("invalid sql data - remove expense: " + exception.getMessage());
            }

            return result;
        }

在此之后，您也可以通过 Java 以任何您需要的方式转换为 HTML，而不是直接从 SQL 转换。

希望这会有所帮助。