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Java Database Connectivity（JDBC）是Java编程语言中用于与各种数据库进行交互的一种标准接口。它由Sun Microsystems（现为Oracle公司）开发，是Java平台的一部分，允许Java开发者执行SQL语句并处理返回的结果。JDBC提供了数据库连接、数据查询、数据更新等功能，使得Java应用程序能够与多种类型的数据库进行无缝连接。在JDBC中，数据库连接通常通过DriverManager类来建立。我们需要在程序中加载相应的数据库驱动，这通常通过`Class.forName()`方法完成。例如，如果使用的是MySQL数据库，加载驱动的代码可能如下： ```java Class.forName("com.mysql.jdbc.Driver"); ``` 接着，我们使用`DriverManager.getConnection()`方法创建数据库连接，需要提供数据库URL、用户名和密码： ```java Connection conn = DriverManager.getConnection( "jdbc:mysql://localhost:3306/mydatabase", "username", "password"); ``` 一旦建立了连接，就可以通过Statement或PreparedStatement对象来执行SQL语句。Statement用于执行静态SQL，而PreparedStatement允许预编译SQL，提高性能，并防止SQL注入攻击。例如： ```java Statement stmt = conn.createStatement(); String sql = "SELECT * FROM mytable"; ResultSet rs = stmt.executeQuery(sql); ``` ResultSet对象包含了查询结果，可以通过迭代遍历获取每一行数据： ```java while (rs.next()) { int id = rs.getInt("id"); String name = rs.getString("name"); // ... 处理其他列 ... } ``` 对于数据的插入、更新和删除，使用executeUpdate()方法，它返回受影响的行数： ```java String sql = "INSERT INTO mytable (name, age) VALUES (?, ?)"; PreparedStatement pstmt = conn.prepareStatement(sql); pstmt.setString(1, "John"); pstmt.setInt(2, 30); int rowsAffected = pstmt.executeUpdate(); ``` 事务管理也是JDBC的重要部分。通过Connection对象的setAutoCommit()和commit()方法，可以控制事务的提交和回滚： ```java conn.setAutoCommit(false); // 关闭自动提交 // 执行一系列操作... if (allGood) { conn.commit(); // 提交事务 } else { conn.rollback(); // 回滚事务 } ``` 在完成所有数据库操作后，记得关闭资源，以释放数据库连接和其他资源： ```java stmt.close(); rs.close(); conn.close(); ``` `JdbcApp.java`可能是实现上述JDBC操作的Java源代码文件，可能包含了连接数据库、执行SQL语句、处理结果集以及关闭资源的完整流程。通过阅读和理解这个文件，你可以更深入地了解如何在实际项目中使用JDBC。 JDBC是Java开发人员连接和操作数据库的核心工具，无论是在小型应用程序还是大型企业级系统中，它都扮演着不可或缺的角色。通过熟练掌握JDBC，开发者可以构建健壮、高效的数据库应用。

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Jdbc.zip （1个子文件）

JdbcApp.java 7KB

/* database connectivity with MS-Access is done by creating DataSourceName(dsn) in this example*/ /* Steps : * go to ms-access and make a table called "student_db" and give it a file name student_db.mdb * 1. Go to Control Panel 2. Click on Administrative Tools(windows 2000/xp) 3. click on ODBC Database source 4. Then , you will see a ODBC dialog box. Click on UserDSn 5. Click on Add Button 6. Select Microsoft Access Driver(*.mdb) driver and click on finish 7. Give a Data Source Name : student_db 8. Then Click on create 9. give the database name student_db. give any path to the file 10. Click on OK. Once the DSN is created, you can do this*/ import javax.swing.*; import javax.swing.table.*; import javax.swing.ListSelectionModel.*; import javax.swing.event.ListSelectionEvent; import javax.swing.event.ListSelectionListener; import java.awt.*; import java.awt.event.*; import java.sql.*; class InputDialog extends JDialog implements ActionListener{ String s; JTextField tf; JButton b; InputDialog(Frame parent,String title,boolean mode) { super(parent,title,mode); setLayout(new FlowLayout()); setSize(150,100); setLocation(550, 300); add(tf = new JTextField(10)); add(b = new JButton("Ok")); b.addActionListener(this); show(); } public String getInput() { return s; } public void actionPerformed(ActionEvent e) { s=tf.getText(); dispose(); } } public class JdbcApp extends JFrame implements ActionListener{ JButton BtnInsert,BtnUpdate,BtnShow; JTextField TfRollno,TfName,TfMark; JTable Table; DefaultTableModel Model; Panel PLeft,PRight; Container ContentPane; Connection Con; int r,c; JdbcApp() { ContentPane = getContentPane() ; ContentPane.setLayout(new BorderLayout(2,5)); TfRollno = new JTextField(15); TfName = new JTextField(15); TfMark = new JTextField(15); BtnInsert = new JButton("Insert") ; BtnInsert.addActionListener(this); PLeft = new Panel(); PLeft.setLayout(new GridLayout(7,1,2,2)); PLeft.add(new JLabel("Roll No:")); PLeft.add(TfRollno); PLeft.add(new JLabel("Name:")); PLeft.add(TfName); PLeft.add(new JLabel("Mark:")); PLeft.add(TfMark); PLeft.add(BtnInsert); ContentPane.add(PLeft,BorderLayout.WEST); BtnUpdate = new JButton("Update"); BtnUpdate.addActionListener(this); BtnShow = new JButton("Show"); BtnShow.addActionListener(this); PRight = new Panel(); PRight.setLayout(new FlowLayout()); PRight.add(BtnUpdate); PRight.add(BtnShow); ContentPane.add(PRight,BorderLayout.SOUTH); Model = new DefaultTableModel(); Table = new JTable(Model){ public boolean isCellEditable(int row,int column) { return false; } }; Model.addColumn("Roll No"); Model.addColumn("Name"); Model.addColumn("Mark"); Table.setCellSelectionEnabled(true); ListSelectionModel cellSelectionModel = Table.getSelectionModel(); cellSelectionModel.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); cellSelectionModel.addListSelectionListener(new ListSelectionListener() { public void valueChanged(ListSelectionEvent e) { c=Table.getSelectedColumn(); r=Table.getSelectedRow(); } }); int v = ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED; int h = ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED; JScrollPane jsp = new JScrollPane(Table,v,h); ContentPane.add(jsp); setSize(700,300); setLocation(300,200); setVisible(true); setResizable(false); setDefaultCloseOperation(EXIT_ON_CLOSE); try{ //loading the driver Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); //connection object created using DriverManager class //student_base is the name of the database Con = DriverManager.getConnection("jdbc:odbc:student_db"); //create a table student Statement Stmnt = Con.createStatement(); Stmnt.executeUpdate("create table student (Rollno integer, Name varchar(30),Mark integer)"); } catch(Exception e) { JDialog Ed = new JDialog(this,"Error",true); Ed.add(new JLabel(e.toString(),JLabel.CENTER)); Ed.setSize(700, 100); Ed.setLocation(350, 300); Ed.show(); } } public void showMessage(String m) { JDialog Ed = new JDialog(this,"Message",true); Ed.add(new JLabel(m,JLabel.CENTER)); Ed.setSize(700, 100); Ed.setLocation(350, 300); Ed.show(); } public static void main(String args[]) { JdbcApp app = new JdbcApp() ; } public void actionPerformed(ActionEvent e) { try { if(e.getActionCommand()=="Update") { if(Table.isRowSelected(r)) { InputDialog dialog = new InputDialog(this,"Enter new value",true); if(!dialog.getInput().isEmpty()) { Statement stmt = Con.createStatement(); stmt.executeUpdate("update student set " +Table.getColumnName(c)+ " =\'" + dialog.getInput() +"\' where Rollno=" + Table.getValueAt(r, 0) ); showMessage("One row updated successfully...."); } } } else if(e.getActionCommand()=="Insert") { PreparedStatement pstm = Con.prepareStatement("insert into student values(?,?,?)"); pstm.setInt(1,Integer.parseInt(TfRollno.getText())); pstm.setString(2,TfName.getText()); pstm.setInt(3,Integer.parseInt(TfMark.getText())); pstm.executeUpdate(); TfRollno.setText(""); TfName.setText(""); TfMark.setText(""); showMessage("One row inserted successfully......"); } else if(e.getActionCommand()=="Show") { int i =0; Statement stmt = Con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_READ_ONLY); ResultSet rs = stmt.executeQuery("select Rollno,Name,Mark from student"); Model.setRowCount(0); while(rs.next()) { Model.insertRow(i,new Object[]{rs.getInt(1),rs.getString(2),rs.getInt(3)}); i++; } } } catch(Exception ex) { JDialog Ed = new JDialog(this,"Error",true); Ed.add(new JLabel(ex.toString(),JLabel.CENTER)); Ed.setSize(700, 100); Ed.setLocation(350, 300); Ed.show(); } } }

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