public class User {
  private Integer id;
  private String name;
  private String pass;
  private Integer age;
}

public class User {
  private Integer id;
  private String name;
  private String pass;
  private Integer age;
  public User() {
  }
  public User(String name, String pass, Integer age) {
    this.name = name;
    this.pass = pass;
    this.age = age;
  }
  public User(Integer id, String name, String pass, Integer age) {
    this.id = id;
    this.name = name;
    this.pass = pass;
    this.age = age;
  }
  public Integer getAge() {
    return age;
  }
  public void setAge(Integer age) {
    this.age = age;
  }
  public Integer getId() {
    return id;
  }
  public void setId(Integer id) {
    this.id = id;
  }
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public String getPass() {
    return pass;
  }
  public void setPass(String pass) {
    this.pass = pass;
  }
}

public static final String URL = "jdbc:mysql://localhost:3306/testdb";
public static final String USER = "testuser";
public static final String PASS = "testpass";
/**
 * 获取connection对象
 * @return Connection 对象
*/
public static Connection getConnection() {
  try {
    DriverManager.registerDriver(new Driver());
    return DriverManager.getConnection(URL, USER, PASS);
  } catch (SQLException ex) {
    throw new RuntimeException("Error connecting to the database", ex);
  }
}

import com.mysql.jdbc.Driver;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
/**
 * Connect to Database
 * @author hany.said
 */
public class ConnectionFactory {
  public static final String URL = "jdbc:mysql://localhost:3306/testdb";
  public static final String USER = "testuser";
  public static final String PASS = "testpass";
  /**
   * Get a connection to database
   * @return Connection object
   */
  public static Connection getConnection()
  {
   try {
     DriverManager.registerDriver(new Driver());
     return DriverManager.getConnection(URL, USER, PASS);
   } catch (SQLException ex) {
     throw new RuntimeException("Error connecting to the database", ex);
   }
  }
  /**
   * Test Connection
   */
  public static void main(String[] args) {
    Connection connection = connectionFactory.getConnection();
  }
}

public interface UserDao {
  User getUser();
  Set<User> getAllUsers();
  User getUserByUserNameAndPassword();
  boolean insertUser();
  boolean updateUser();
  boolean deleteUser();
}

public User getUser(int id) {
  Connection connection = connectionFactory.getConnection();
    try {
      Statement stmt = connection.createStatement();
      ResultSet rs = stmt.executeQuery("SELECT * FROM user WHERE id=" + id);
      if(rs.next())
      {
        User user = new User();
        user.setId( rs.getInt("id") );
        user.setName( rs.getString("name") );
        user.setPass( rs.getString("pass") );
        user.setAge( rs.getInt("age") );
        return user;
      }
    } catch (SQLException ex) {
      ex.printStackTrace();
    }
  return null;
}

private User extractUserFromResultSet(ResultSet rs) throws SQLException {
  User user = new User();
  user.setId( rs.getInt("id") );
  user.setName( rs.getString("name") );
  user.setPass( rs.getString("pass") );
  user.setAge( rs.getInt("age") );
  return user;
}

public User getUser(int id) {
  Connection connection = connectionFactory.getConnection();
  try {
    Statement stmt = connection.createStatement();
    ResultSet rs = stmt.executeQuery("SELECT * FROM user WHERE id=" + id);
    if(rs.next())
    {
      return extractUserFromResultSet(rs);
    }
  } catch (SQLException ex) {
    ex.printStackTrace();
  }
  return null;
}

public User getUserByUserNameAndPassword(String user, String pass) {
  Connector connector = new Connector();
  Connection connection = connector.getConnection();
  try {
    PreparedStatement ps = connection.prepareStatement("SELECT * FROM user WHERE user=? AND pass=?");
    ps.setString(1, user);
    ps.setString(2, pass);
    ResultSet rs = ps.executeQuery();
    if(rs.next())
    {
  return extractUserFromResultSet(rs);
    }
  } catch (SQLException ex) {
    ex.printStackTrace();
  }
  return null;
}

public Set getAllUsers() {
  Connector connector = new Connector();
  Connection connection = connector.getConnection();
  try {
    Statement stmt = connection.createStatement();
    ResultSet rs = stmt.executeQuery("SELECT * FROM user");
    Set users = new HashSet();
    while(rs.next())
    {
      User user = extractUserFromResultSet(rs);
      users.add(user);
    }
    return users;
  } catch (SQLException ex) {
    ex.printStackTrace();
  }
  return null;
}
 

public boolean insertUser(User user) {
  Connector connector = new Connector();
  Connection connection = connector.getConnection();
  try {
    PreparedStatement ps = connection.prepareStatement("INSERT INTO user VALUES (NULL, ?, ?, ?)");
    ps.setString(1, user.getName());
    ps.setString(2, user.getPass());
    ps.setInt(3, user.getAge());
    int i = ps.executeUpdate();
   if(i == 1) {
    return true;
   }
  } catch (SQLException ex) {
    ex.printStackTrace();
  }
  return false;
}
 

public boolean updateUser(User user) {
  Connector connector = new Connector();
  Connection connection = connector.getConnection();
  try {
    PreparedStatement ps = connection.prepareStatement("UPDATE user SET name=?, pass=?, age=? WHERE id=?");
    ps.setString(1, user.getName());
    ps.setString(2, user.getPass());
    ps.setInt(3, user.getAge());
    ps.setInt(4, user.getId());
    int i = ps.executeUpdate();
   if(i == 1) {
  return true;
   }
  } catch (SQLException ex) {
    ex.printStackTrace();
  }
  return false;
}
 

public boolean deleteUser(int id) {
  Connector connector = new Connector();
  Connection connection = connector.getConnection();
  try {
    Statement stmt = connection.createStatement();
    int i = stmt.executeUpdate("DELETE FROM user WHERE id=" + id);
   if(i == 1) {
  return true;
   }
  } catch (SQLException ex) {
    ex.printStackTrace();
  }
  return false;
}