从 MySQL DB 检索数据并显示在 JTable 中

Question

我正在使用以下代码从 MySQL 数据库检索数据。代码正确连接到数据库。我的问题是从 MySQL DB 检索数据并将其显示在 JTable 中。

package student;
import java.awt.*;
import javax.swing.*;
import java.awt.*;
import java.sql.*;
import java.util.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.table.*;

public class student1 extends javax.swing.JFrame {
    // public Connection Conn;
    Vector data = new Vector() ;
    Vector columnNames= new Vector();

    public student1() {
        initComponents();
        Connection conn;
    }

    public void Connection(){
        try
        {
            Class.forName("com.mysql.jdbc.Driver");
            String username = "root";
            String password = "root";
            String Database = "jdbc:mysql://localhost:3306/project";
            Connection conn = DriverManager.getConnection(Database, username, password);
            System.out.println("*** Connect to the database ***");
            String Query = "Select * from  StudentMaster";
            Statement smnt = conn.createStatement();
            ResultSet results = smnt.executeQuery( Query );
            ResultSetMetaData metaDt = results.getMetaData();
            System.out.println(metaDt);

            int cols = metaDt.getColumnCount();
            System.out.println("database" +cols);
            for(int i=1;i<cols;i++){
                columnNames.addElement (metaDt.getColumnName(i));
            }
            while(results.next()){
                Vector row= new Vector(cols);
                for(int i=1;i<=cols;i++){
                    row.addElement(results.getObject(i));
                }
                data.addElement(row);
            }
            results.close();
            smnt.close();
            conn.close();
        }
        catch(Exception e)
        {
            System.out.println(e);
        }
    }

    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {
        jScrollPane1 = new javax.swing.JScrollPane();
        jTable1 = new javax.swing.JTable();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jTable1.setModel(new javax.swing.table.DefaultTableModel(
            new Object [][] {
                {null, null, null, null, null, null, null, null},
                {null, null, null, null, null, null, null, null},
                {null, null, null, null, null, null, null, null},
                {null, null, null, null, null, null, null, null}
            },
            new String [] {
                "StudId", "StudNo", "StudName", "StudClass", "StudMrk1", "StudMrk2", "StudTot", "StudRes"
            }
        ){
            Class[] types = new Class [] {
                java.lang.Integer.class, java.lang.Integer.class, java.lang.String.class, java.lang.Integer.class, java.lang.Integer.class, java.lang.String.class, java.lang.Integer.class, java.lang.String.class
            };

            public Class getColumnClass(int columnIndex) {
                return types [columnIndex];
            }
        });
        jScrollPane1.setViewportView(jTable1);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 560, Short.MAX_VALUE)
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 88, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(212, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>

    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new student1().setVisible(true);
               student1 s1=new student1();
               s1.Connection();

            }
        });
    }

    // Variables declaration - do not modify
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTable jTable1;
    // End of variables declaration
}

当我执行这段代码时，我得到以下输出。我该如何解决我的问题？

*** Connect to the database ***
com.mysql.jdbc.ResultSetMetaData@1194a4e - Field level information: 
        com.mysql.jdbc.Field@15d56d5[catalog=project,tableName=StudentMaster,originalTableName=studentmaster,columnName=StudId,originalColumnName=StudId,mysqlType=3(FIELD_TYPE_LONG),flags= PRIMARY_KEY, charsetIndex=63, charsetName=US-ASCII]
        com.mysql.jdbc.Field@efd552[catalog=project,tableName=StudentMaster,originalTableName=studentmaster,columnName=StudNo,originalColumnName=StudNo,mysqlType=3(FIELD_TYPE_LONG),flags=, charsetIndex=63, charsetName=US-ASCII]
        com.mysql.jdbc.Field@19dfbff[catalog=project,tableName=StudentMaster,originalTableName=studentmaster,columnName=StudName,originalColumnName=StudName,mysqlType=253(FIELD_TYPE_VAR_STRING),flags=, charsetIndex=8, charsetName=Cp1252]
        com.mysql.jdbc.Field@10b4b2f[catalog=project,tableName=StudentMaster,originalTableName=studentmaster,columnName=StudClass,originalColumnName=StudClass,mysqlType=253(FIELD_TYPE_VAR_STRING),flags=, charsetIndex=8, charsetName=Cp1252]
        com.mysql.jdbc.Field@750159[catalog=project,tableName=StudentMaster,originalTableName=studentmaster,columnName=StudMrk1,originalColumnName=StudMrk1,mysqlType=3(FIELD_TYPE_LONG),flags=, charsetIndex=63, charsetName=US-ASCII]
        com.mysql.jdbc.Field@1abab88[catalog=project,tableName=StudentMaster,originalTableName=studentmaster,columnName=StudMrk2,originalColumnName=StudMrk2,mysqlType=3(FIELD_TYPE_LONG),flags=, charsetIndex=63, charsetName=US-ASCII]
        com.mysql.jdbc.Field@18a7efd[catalog=project,tableName=StudentMaster,originalTableName=studentmaster,columnName=StudTot,originalColumnName=StudTot,mysqlType=3(FIELD_TYPE_LONG),flags=, charsetIndex=63, charsetName=US-ASCII]
        com.mysql.jdbc.Field@1971afc[catalog=project,tableName=StudentMaster,originalTableName=studentmaster,columnName=StudRes,originalColumnName=StudRes,mysqlType=253(FIELD_TYPE_VAR_STRING),flags=, charsetIndex=8, charsetName=Cp1252]
database8
BUILD SUCCESSFUL (total time: 14 seconds)

Answer 1

我没有看到任何错误。您看到的是从代码中打印的消息，主要来自这些语句：

ResultSetMetaData metaDt = results.getMetaData();
System.out.println(metaDt);
int cols = metaDt.getColumnCount();
System.out.println("database" +cols);

Answer 2

您的基本代码看起来很合理。您创建两个包含列名称和数据的向量，但随后您无法在哪里使用这些向量来创建 DefaultTableModel，然后将其添加到表中。

因此，您的代码应该类似于：

conn.close();
DefaultTableModel model = new DefaultTableModel(data, columnNames);
table.setModel( model );

有关完整的示例（使用 Access），请查看 数据库中的表。