单一职责原则
登录模块在实际项目开发中很常见，请按照教材28页利用单一职责原则重构后的类图实现这
一模块。
1.类图：
2.java代码实现:
（1）DBUtil.java：
package test;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class DBUtil {
public static String db_url = "jdbc:mysql://localhost:3306/first?serverTimezone=GMT%2B8&useSSL=false";
public static String db_user = "root";
public static String db_pass = "root";
public static Connection getConn () {
Connection conn = null;
try {
Class.forName("com.mysql.cj.jdbc.Driver");
conn = DriverManager.getConnection(db_url, db_user, db_pass);
} catch (Exception e) {
e.printStackTrace();
}
return conn;
}//end getConn
public static void close (Statement state, Connection conn) {
if (state != null) {
try {
state.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
public static void close (ResultSet rs, Statement state, Connection conn) {
if (rs != null) {
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (state != null) {
try {
state.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) throws SQLException {
Connection conn = getConn();
PreparedStatement pstmt = null;
ResultSet rs = null;
String sql ="select * from user";
pstmt = conn.prepareStatement(sql);
rs = pstmt.executeQuery();
if(rs.next()){
System.out.println("连接成功");
}else{
System.out.println("连接失败");
}
}
}
（2）UserDao.java:
package test;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class UserDao {
public boolean findUser(String username, String password) {
//准备SQL语句
String sql = "select * from user where username ='" + username + "'";
Connection conn= DBUtil.getConn();
//创建语句传输对象
Statement state = null;
ResultSet rs= null;
int flag=0;
String c_password=null;
try {
state = conn.createStatement();
rs = state.executeQuery(sql);
while(rs.next()) {
++flag;
c_password=rs.getString("password");
} if (flag == 0) {
return false;
}
if (!password.equals(c_password)) { //判断密码
return false;
}
}catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally {
DBUtil.close(rs, state, conn);
}
return true;
}
}
（3）LoginForm.java:
package test;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class LoginForm extends JFrame {
private static final long serialVersionUID = 1L;
private UserDao dao = new UserDao();
//设置按钮组件
private JButton jb=new JButton("登录"); //添加一个登录按钮
private JButton button=new JButton("重置"); //添加一个确定按钮
//设置文本框组件
private JTextField username = new JTextField();//用户名框
private JPasswordField password = new JPasswordField();//密码框：为加密的***
JLabel user_name=new JLabel("账号：");//设置左侧用户名文字
JLabel pass_word=new JLabel("密码：");//设置左侧密码文字
public void init()
{
/* 组件绝对位置 */
user_name.setBounds(50, 70, 300, 25);
pass_word.setBounds(50, 130, 200, 25);
username.setBounds(110, 70, 300, 25);//设置用户名框的宽，高，x值，y值
password.setBounds(110, 130, 300, 25);//设置密码框的宽，高，x值，y值
button.setBounds(315, 225, 90, 20);//设置确定按钮的宽，高，x值，y值
jb.setBounds(95, 225, 90, 20);//设置确定按钮的宽，高，x值，y值
/* 组件透明化*/
user_name.setOpaque(false);
pass_word.setOpaque(false);
//监听事件
jb.addActionListener(new ActionListener(){ //为确定按钮添加监听事件
@SuppressWarnings("deprecation")
public void actionPerformed(ActionEvent arg0) {
validate(username.getText().trim(),password.getText().trim());
}
});
//重置按钮
button.addActionListener(new ActionListener(){ //为重置按钮添加监听事件
//同时清空name、password的数据
public void actionPerformed(ActionEvent arg0) {
// TODO 自动生成方法存根
username.setText("");
password.setText("");
}
});
}
public void display()
{
JFrame f =new JFrame();
f.setTitle("登录页面");
//窗口退出行为
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//设置窗口大小不可变
f.setResizable(false);
//设置窗口打开居中
f.setLocationRelativeTo(null);
//窗口大小
f.setSize(500, 300);
init();
//添加组件
Container contentPanel= new Container();//添加一个contentPanel容器
contentPanel.setLayout(null);//设置添加的contentPanel容器为流布局管理器
contentPanel.add(user_name);
contentPanel.add(pass_word);
contentPanel.add(username);
contentPanel.add(password);
contentPanel.add(jb);
contentPanel.add(button);
f.add(contentPanel);
//展示窗口
f.setVisible(true);
}
public void validate(String username,String password)
{
if(username.trim().length()==0||password.trim().length()==0){
JOptionPane.showMessageDialog(null, "用户名,密码不允许为空");
return;
}
if(dao.findUser(username, password))
{
JOptionPane.showMessageDialog(null, "登录成功！");
}else {
JOptionPane.showMessageDialog(null, "用户名或密码错误");
}
}
}
（4）MainClass.java:
package test;
public class MainClass {
public static void main(String[] args)
{
LoginForm loginForm=new LoginForm() ; //调用
loginForm.display();
}
}
数据库设计：
实现截图：
