Question

我正在编写连接MySQL数据库的java代码。我有一个连接，但我无法将数据显示在我的JFrame中的标签中。所以我已连接到我的XAMPP数据库中的数据库软件，但我无法将数据显示在标签中

ResultSet rs;
ResultSetMetaData rsmd = null;
int colCount = 0;
String[] colNames = null;

    try {
        rs = engine.executeQuery("select * from music");
        rsmd = rs.getMetaData();
        colCount = rsmd.getColumnCount();
        colNames = new String[colCount];
        for (int i = 1; i <= colCount; i++) {
            colNames[i - 1] = rsmd.getColumnName(i);
        }

        String[] currentRow = new String[colCount];// array to hold the
                                                    // row data
        while (rs.next()) { // move the rs pointer on to the next record
                            // (starts before the 1st)
            for (int i = 1; i <= colCount; i++) {
                currentRow[i - 1] = rs.getString(i);
            }
        }

    //System.out.println(authenticated);

    }
    catch (SQLException a)
    {
        System.err.println("SQLException: " + a.getMessage());
    }

Answer 1

将此代码用于其工作

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;

import java.sql.ResultSetMetaData;

public class Db {
    public static void main(String arg[]) throws SQLException,
            ClassNotFoundException {
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection(
                "jdbc:mysql://localhost/dbname", "root", "");

        java.sql.Statement stmt = conn.createStatement();
        String query = "select * from music";

        ResultSet rs = stmt.executeQuery(query);
        ResultSetMetaData rsmd = rs.getMetaData();

        int columncount = rsmd.getColumnCount();

        for(int i = 1 ; i < columncount ; i ++)
            System.out.print(rsmd.getColumnName(i));

        System.out.println();

        while (rs.next()) {

            for(int i = 1 ; i < columncount ; i ++)
            {
                System.out.print(rs.getString(i));
            }
            System.out.println();
        }

        conn.close();

    }

}

Answer 2

由于您希望为数据库连接提供单独的类，并在其他地方使用此连接，您可以执行以下操作。

public class SQLConnect {
    public static Connection ConnectDb() {
        try { 
            Class.forName("com.mysql.jdbc.Driver");
            Connection conn = null;
            try {
                conn = DriverManager.getConnection("jdbc:mysql://localhost/databasename", "root", "");
            } catch (SQLException ex) {
                Logger.getLogger(SQLConnect.class.getName()).log(Level.SEVERE, null, ex);
            }
            return conn;
        }
        catch (ClassNotFoundException e) {
            System.out.println("not connected");
            e.printStackTrace();//print extra info if error is thrown
            return null; 
        }
    }
}

使用此课程如下

Connection conn = null;
ResultSet rs = null;
PreparedStatement pst = null;

try {
    conn = SQLConnect.ConnectDb();
    String sql = "SELECT * FROM somedatabase WHERE somevalue = ? ";
    pst = conn.prepareStatement(sql);
    pst.setString(1, CriminalID);
    rs = pst.executeQuery();

    if(rs.next()) {
        /*
         * set values of labels to those from database
         */
         jLabel.setText(rs.getString("Column name"));
    }

这将从数据库获取数据，其中某些值等于您指定的任何值

以java形式读取数据MySQL

2 个答案: