數(shù)據(jù)庫(kù)查詢
利用Connection對(duì)象的createStatement方法建立Statement對(duì)象，利用Statement對(duì)象的executeQuery()方法執(zhí)行SQL查詢語(yǔ)句進(jìn)行查詢，返回結(jié)果集，再形如getXXX()的方法從結(jié)果集中讀取數(shù)據(jù)。經(jīng)過這樣的一系列步驟就能實(shí)現(xiàn)對(duì)數(shù)據(jù)庫(kù)的查詢。
【例】Java應(yīng)用程序訪問數(shù)據(jù)庫(kù)。應(yīng)用程序打開考生信息表ksInfo，從中取出考生的各項(xiàng)信息。設(shè)考生信息數(shù)據(jù)庫(kù)的結(jié)構(gòu)如下：
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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"); //加載ODBC驅(qū)動(dòng)程序 } catch (Exception e){ e.printStackTrace(); return null; //加載失敗，連接不成功 } try{ con = DriverManager.getConnection(url, username, password); } catch (SQLException e){ e.printStackTrace(); return null; //連接失敗 } return con; //連接成功 } String title[] ={"考號(hào)", "姓名", "成績(jī)", "地址", "簡(jiǎn)歷"}; 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("前一個(gè)"); JButton next = new JButton("后一個(gè)"); JButton first = new JButton("第一個(gè)"); JButton last = new JButton("最后一個(gè)"); Statement sql; //SQL語(yǔ)句對(duì)象 ResultSet rs; //存放查詢結(jié)果對(duì)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, "請(qǐng)輸入考生考號(hào)", "輸入考號(hào)對(duì)話框", 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("考號(hào)")); txtName.setText(rs.getString("姓名")); txtScore.setText(rs.getString("成績(jī)")); txtAddr.setText(rs.getString("地址")); txtResume.setText(rs.getString("簡(jiǎn)歷")); } 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, "數(shù)據(jù)庫(kù)連接失敗!"); System.exit ( - 1); } new Example10_9(connect); //創(chuàng)建對(duì)象 }} |
Java數(shù)據(jù)庫(kù)更新
數(shù)據(jù)庫(kù)更新操作包括數(shù)據(jù)表創(chuàng)建、刪除、以及數(shù)據(jù)表記錄的增加、刪除、修改等操作。如果利用數(shù)據(jù) SQL命令實(shí)現(xiàn)，則利用Statement對(duì)旬的executeUpdate()方法，執(zhí)行SQL的update語(yǔ)句，實(shí)現(xiàn)數(shù)據(jù)表的修改；執(zhí)行SQL的insert語(yǔ)句，實(shí)現(xiàn)數(shù)據(jù)表記錄的添加。
例如，在前面數(shù)據(jù)為查詢例子基礎(chǔ)上，再增加對(duì)數(shù)據(jù)表的修改和插入。限于篇幅，不再給出完整程序，只給出實(shí)現(xiàn)修改和插入的方法。程序可再增設(shè)插入、，，除保存按鈕，通過已有的瀏覽，定位到數(shù)據(jù)表的特定位置，對(duì)癰疽記錄進(jìn)行編輯修改，或插入，或刪除，然后按保存按鈕，完成修改后的數(shù)據(jù)表保存。
下面用代碼說(shuō)明數(shù)據(jù)表更新的方法。與數(shù)據(jù)表連接時(shí)，需指定獲得的ResultSet 對(duì)象是可更新的。
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stmt = connect.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE); |
