Detailed explanation of Java's query and update operations on the database

This article mainly introduces the use of Java to perform basic query and update operations on the database. It is the basic knowledge for Getting Started with Java. Friends who need it can refer to it

Database query

Use the createStatement method of the Connection object to create a Statement object, use the executeQuery() method of the Statement object to execute the SQL query statement and return the result set, and then use the getXXX() method from Data is read in the result set. After such a series of steps, the query to the database can be realized.

[Example] Java application accesses the database. The application opens the candidate information table ksInfo and retrieves various information about the candidate. Assume that the structure of the candidate information database is as follows:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.sql.*;
public class Example10_9 extends JFrame implements ActionListener{
  public static Connection connectByJdbcodbc(String url, String username,String password){
    Connection con = null;
    try{
      Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); //加载ODBC驱动程序
    }
    catch (Exception e){
      e.printStackTrace();
      return null; //加载失败，连接不成功
    }
    try{
      con = DriverManager.getConnection(url, username, password);
    }
    catch (SQLException e){
      e.printStackTrace();
      return null; //连接失败
    }
    return con; //连接成功
  }
  String title[] ={"考号", "姓名", "成绩", "地址", "简历"};
  JTextField txtNo = new JTextField(8);
  JTextField txtName = new JTextField(10);
  JTextField txtScore = new JTextField(3);
  JTextField txtAddr = new JTextField(30);
  JTextArea txtresume = new JTextArea();
  JButton prev = new JButton("前一个");
  JButton next = new JButton("后一个");
  JButton first = new JButton("第一个");
  JButton last = new JButton("最后一个");
  Statement sql; //SQL语句对象
  ResultSet rs; //存放查询结果对象
  Example10_9(Connection connect){
    super("考生信息查看窗口");
    setSize(450, 350);
    try{
      sql = connect.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
      rs = sql.executeQuery("SELECT * FROM ksInfo");
      Container con = getContentPane();
      con.setLayout(new BorderLayout(0, 6); JPanel p[] = new JPanel[4];
      for (int i = 0; i < 4; i++){
        p[i] = new JPane(new FlowLayout(FlowLayout.LEFT, 8, 0));
        p[i].add(new JLabel(title[i]));
      }
      p[0].add(txtNo);
      p[1].add(txtName);
      p[2].add(txtScore);
      p[3].add(txtAddr);
      JPanel p1 = new JPane(new GridLayout94, 1, 0, 8));
      JScrollPane jsp = new JScrollPane(txtResume,
        JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
        JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
        jsp.setPreforredSize(new Dimension(300, 60);
      for (int i = 0; i < 4; i++){
        p1.add(p[i]);
      }
      JPanel p2 = new JPanel(new FlowLayout(FlowLayout.LEFT, 10, 0);
      p2.add(new JLabel(title[4]));
      p2.add(jsp);
      Jpanel p3 = new Jpanel();
      p3.add(prev);
      p3.add(next);
      p3.add(first);
      p3.add(last);
      prev.addActionListener(this);
      next.addActionListener(this);
      first.addActionListener(this);
      last.addActionlistener(this);
      rs.first();
      readRecord();
    }
    catch (Exception e){
      e.printStackTrace():
    }
    setVisible(ture);
  }
  public void modifyRecord(Connection connect){
    String stuNo = (String)JOptionPane.showInputDialog(null,
      "请输入考生考号", "输入考号对话框", JOptionPane.PLAIN_MESSAGE, null,
      null, "");
    try {
      sql = connect.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
      rs = sql.executeQuery("SELECT * FROM ksInfo");
      Container con = getContentPane();
      con.setLayout(new Boarderlayout(0, 6));
      Jpanel p[] = new JPanel[4];
      for (int i = 0; i < ; i++){
        p[i] = new JPane(new FlowLayout(flowLayout.LEFT, 8, 0));
        p[i].add(new JLabel(title[i]));
      }
      p[0].add(txtNo);
      p[1].add(txtName);
      p[2].add(txtScore);
      p[3].add(txtAddr);
      Jpanel p1 = new Jpane(new GridLayout(4, 1, 0, 8));
      JScrollPane jsp = new JScrollPane(txtResume,
        JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
        JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
      jsp.setPreferredSize (new dimension(300, 60));
      for (int i = 0; i < 4; i++){
        p1.add(p[i]);
      }
      Jpanel p2 = new JPanel(new FlowLayout(FlowLayout.LEFT, 10, 0));
      p2.add(new JLableI(title[4]));
      p2.add(jsp);
      JPanel p3 = new JPanel();
      p3.add(prev);
      p3.add(next);
      p3.add(first);
      p3.add(last);
      prev.addActionListener(this);
      next.addActionListener(this);
      first.addActionListenerIthis);
      last.addActionListener(this);
      rs.first();
      readRecord();
    }
    catch (Exception e){
      e.printStackTrace();
    }
    setVisible(true);
  }
  boolean readRecord(){
    try{
      txtNo.setText(rs.getString("考号")); txtName.setText(rs.getString("姓名")); txtScore.setText(rs.getString("成绩"));
      txtAddr.setText(rs.getString("地址")); txtResume.setText(rs.getString("简历"));
    }
    catch (SQLException e){
      e.printStackTrace(); return false;
    }
    return true;
  }
  public void actionPerformed(ActionEvent e){
    try{
      if (e.getSource() == prev)rs.previous();
      else if (e.getSource() == next)rs.next();
      else if (e.getSource() == first)rs.first();
      else if (e.getSource() == last)rs.last(); readRecord();
    }
    catch (Exception e2){}
  }
  public static void main(String args[]){
    connection connect = null;
    JFrame .setDefaultLookAndFeeDecorated(true);
    Font font = new Font("JFrame", Font.PLAIN, 14);
    if ((connect =connectByJdbcOdbc("jdbc:odbc:redsun", "xia", "1234")) == null){
      JOptionPane.showMessageDialog(null, "数据库连接失败!");
      System.exit ( - 1);
    }
    new Example10_9(connect); //创建对象
  }
}

Java database update
Database update operations include data table creation and delete, and operations such as adding, deleting, and modifying data table records. If it is implemented using data SQL commands, use the executeUpdate() method of the Statement pair to execute the SQL update statement to modify the data table; execute the SQL insert statement to add the data table records.

For example, based on the previous data query example, add modification and insertion to the data table. Due to space limitations, the complete program will not be given, only the methods to implement modification and insertion. The program can add insert,,, and save buttons. Through the existing browsing, locate a specific position of the data table, edit, modify, insert, or delete the carbuncle record, and then press the save button to complete the modified data table. save.

The following code explains how to update the data table. When connecting to a data table, you need to specify that the ResultSet object obtained is updatable.

  stmt = connect.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE);

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