在 NetBeans 中将 SQL 数据库连接到 JAVA 时出现问题

Question

我尝试用 SQL 连接 netbeans，但还是有问题。我想，还是少了点什么。

在这里，我创建了这个类： （这里现在发生错误 - 另一方面，我真的不知道，如果它是完全正确的）

public class connection {
   public Connection con;

   public void dbConnect(){

     try {  
       Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
       String connectionUrl = "jdbc:sqlserver://FIO\\SQLEXPRESS;" +
           "databaseName=Feedback;integratedSecurity=true";
       con = DriverManager.getConnection(connectionUrl);
    } catch (SQLException e) {
        System.out.println("SQL Exception: "+ e.toString());
    } catch (ClassNotFoundException cE) {
        System.out.println("Class Not Found Exception: "+ cE.toString());   
    }

    }
    public Connection getConnection() {
        return con;
    }

    static PreparedStatement prepareStatement(String sql) {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }

}

然后，在另一个名为 Questions 的类中，我尝试准备语句并从数据库加载信息：

public class Questions {

public void doQuestion()
{...
 ...
 ...
 ...
 connection con = new connection(); 
 con.dbConnect();

 PreparedStatement preparedStatement;


    try{


      **preparedStatement = con.getConnection().createStatement();**


    String sql = "SELECT Answer FROM Feedback.dbo.Question1 WHERE TrainerFirstName=? AND TrainerLastName=?"



    preparedStatement.setString(1,"ffname");

    preparedStatement.setString(2, "llname");

    ResultSet result = preparedStatement.executeQuery(sql);


     while(result.next()) 
     {
     System.out.println(result.getString(1) + result.getString(2));
      }


      }catch (SQLException ex) {
          Logger.getLogger(Questions.class.getName()).log(Level.SEVERE, null, ex);
       }
         ...
          ...
           ...
             ...
              ...
          }
          }

Netbeans 下划线："preparedStatement = con.getConnection().createStatement(); ", due to "incompatible types: Statement cannot be converted to PreparedStatement."

我无法克服它。

然后我尝试做这样的事情来解决问题，但问题仍然存在，即使以不同的方式。：

       public class Questions {

         public void doQuestion()

       {...
        ...
         ...
           ...
          connection con = new connection(); 
          con.dbConnect();

          Statement statement;
    try {
        statement = con.getConnection().createStatement();

     String sql = "SELECT Answer FROM Feedback.dbo.Question1 WHERE TrainerFirstName=?      AND TrainerLastName=?"


        **statement.setString(1,"ffname");
        statement.setString(2, "llname");**

        ResultSet rs = statement.executeQuery(sql);

        while (rs.next()) {
            System.out.println(rs.getString(1) + rs.getString(2));
        }

    } catch (SQLException ex) {
        Logger.getLogger(Questions.class.getName()).log(Level.SEVERE, null, ex);
    }

在这里，Netbeans 下划线 "statement.setString(1,"ffname"); statement.setString(2, "llname");"

由于标签：”找不到符号 符号：方法 setString(int,String) location:variable Statement of type Statement"

然后，我尝试以不同的形式发送 String sql：

           String sql = "SELECT Answer FROM Feedback.dbo.Question1 WHERE TrainerFirstName="+ffname+"AND TrainerLastName="+llname

并以这种方式在代码中省略：
statement.setString(1,"ffname"); statement.setString(2, "llname");

所以，代码看起来像这样：

          public class Questions {

         public void doQuestion()

       {...
        ...
         ...
           ...
          connection con = new connection(); 
          con.dbConnect();

          Statement statement;
    try {
        statement = con.getConnection().createStatement();

         String sql = "SELECT Answer FROM Feedback.dbo.Question1 WHERE TrainerFirstName="+ffname+"AND TrainerLastName="+llname


        ResultSet rs = statement.executeQuery(sql);

        while (rs.next()) {
            System.out.println(rs.getString(1) + rs.getString(2));
        }

    } catch (SQLException ex) {
        Logger.getLogger(Questions.class.getName()).log(Level.SEVERE, null, ex);
    }

这样，一切似乎都OK了，但是当我运行一个项目时，出现错误并指向：“ statement = con.getConnection().createStatement(); ”并且程序当然崩溃了。

我真的不知道该怎么办。

如果有人有想法，请写出来。

非常感谢。

Answer 1

这是 netbeans 的一个preparedstament 的例子

Connection con = null;
PreparedStatement ptmt = null;

public void add(Archivos archivos) {

    try {
        String query = "INSERT INTO archivosemisor "
                + "(rfcEmisor, cer, llave, password, idError, resultado)"
                + " VALUES (?,?,?,?,?,?)";
        con = getConnection();
        ptmt = con.prepareStatement(query);
        ptmt.setString(1, archivos.getRfcEmisor());
        ptmt.setString(2, archivos.getCer());
        ptmt.setString(3, archivos.getLlave());
        ptmt.setString(4, archivos.getPassword());
        ptmt.setString(5, archivos.getIdError());
        ptmt.setString(6, archivos.getResultado());

        ptmt.executeUpdate();

    } catch (SQLException e) {
         .......
    } finally {
            .....
    }

}

希望对你有帮助

Answer 2

在这个简单的例子中，我连接到一个数据库并创建一个语句，但我不使用 con.getConnection().createStatement 而是只使用 con.createStatement() 尝试这样做，这可能是问题所在。我将使用我已经拥有的 I 数据库的整个 sql Demo 留在这里，如果您将来有其他问题，它可能会有所帮助。如果您的问题仍然存在，请告诉我。

public static void main(String[] args) {
    String url = "jdbc:mysql://localhost:3306/";
    String dbName = "pc_control";
    String driver = "com.mysql.jdbc.Driver";
    String userName = "root";
    String password = "";
    try {
        Class.forName(driver).newInstance();
        Connection conn = DriverManager.getConnection(url + dbName, userName, password);
        Statement st = conn.createStatement();
        ResultSet res = st.executeQuery("SELECT * FROM computers");
        while (res.next()) {
            int comp_id = res.getInt("computer_id");
            int emp_id = res.getInt("employee_id");
            String image = res.getString("image");
            String brand = res.getString("brand");
            String model = res.getString("model");
            String m_board = res.getString("m_board");
            String processor = res.getString("processor");
            int ram = res.getInt("ram");
            String hdd = res.getString("hdd");
            String os = res.getString("os");
            String ip_add = res.getString("ip_add");


            System.out.println(comp_id + "\t" + emp_id + "\t" + image + "\t" + brand + "\t" + 
                    model + "\t" + m_board + "\t" + processor + "\t" + ram + "\t" + hdd + "\t" 
                    + os + "\t" + ip_add + "\t");
        }//            
        conn.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

---

更新

尝试以这种方式或类似的方式重新定义您的连接类。

我希望这对你有帮助。很抱歉，我无法指出您的错误，但您的连接实现对我来说有点奇怪。

public class MySqlConnection {

static String url = "jdbc:mysql://localhost:3306/";
static String dbName = "pc_control";
static String driver = "com.mysql.jdbc.Driver";
static String userName = "root";
static String password = "";
static Statement st;
static Connection conn;

public MySqlConnection() {
}

public static boolean connect() {
    try {
        Class.forName(driver).newInstance();
        conn = DriverManager.getConnection(url + dbName, userName, password);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return true;
}

public static ResultSet read(String query) 
{
    ResultSet res = null;
    try {
        st = conn.createStatement();
        res = st.executeQuery(query);
    } catch (SQLException ex) {
        Logger.getLogger(MySqlConnection.class.getName()).log(Level.SEVERE, null, ex);
    }
    return res;
}

}

要进行查询，只需以这种方式调用任何其他类的方法：

String query = "SELECT * FROM computers WHERE computer_id= " + id; //or whatever
ResultSet res = MySqlConnection.read(query);