java工程链接mysql数据库

package com.userdao; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import com.userbean.UserBean; public class UserDAO1 { Connection conn = null; Statement st = null; ResultSet rs = null; public void openDBConnection() { //Connection conn = null; try { Class.forName("org.sqlite.JDBC"); conn = DriverManager.getConnection("jdbc:sqlite:/Users/fanqiliang/mydata"); } catch (Exception e) { e.printStackTrace(); } //return conn; } public UserBean queryUser(String userID) { UserBean ub = new UserBean(); String sql = "select username, password from students"; try { st = conn.createStatement(); rs = st.executeQuery(sql); System.out.println("querying " + userID); while (rs.next()) { if (userID.equals(rs.getString("username"))) { System.out.println(userID +","+ rs.getString("username")); ub.setUsername(rs.getString("username")); ub.setPassword(rs.getString("password")); return ub; } } } catch (Exception e) { e.printStackTrace(); // TODO: handle exception } ub = null; return ub; } public boolean insertUser(UserBean u) { boolean b = false; String sql = "insert into students values(?,?)"; try { PreparedStatement ps = null; ps = conn.prepareStatement(sql); ps.setString(1, u.getUsername()); ps.setString(2, u.getPassword()); if (ps != null) { b = true; ps.executeUpdate(); } } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return b; } public boolean updateUser(UserBean u) { boolean b = false; String sql = "update students set username=? where password=?"; PreparedStatement ps; try { ps = conn.prepareStatement(sql); ps.setString(1, u.getUsername()); ps.setString(2, u.getPassword()); ps.executeUpdate(); b = true; } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return b; } public boolean deleteUser(UserBean u) { boolean b = false; String sql = "delete from students where password=?"; try { PreparedStatement ps = conn.prepareStatement(sql); ps.setString(1, u.getPassword()); ps.executeUpdate(); b = true; } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return b; } public boolean closeDBConnection() { boolean b = true; try { rs.close(); st.close(); conn.close(); } catch (Exception e) { b = false; e.printStackTrace(); // TODO: handle exception } return b; } }