Spring Boot实现简单的登录注册功能

以下是一个简单的Spring Boot应用程序示例，它包含了用户的登录和注册功能。这个例子使用了Spring Security来处理安全相关的功能，并使用了Thymeleaf作为模板引擎来渲染HTML页面。

1. 首先，在pom.xml中添加所需的依赖：

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-security</artifactId>
    </dependency>
    <dependency>
        <groupId>org.thymeleaf</groupId>
        <artifactId>thymeleaf-spring5</artifactId>
    </dependency>
</dependencies>

2. 创建一个简单的User实体类：

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
 
@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String username;
    private String password;
 
    // Getters and setters...
}

3. 创建一个UserRepository接口：

import org.springframework.data.jpa.repository.JpaRepository;
 
public interface UserRepository extends JpaRepository<User, Long> {
    boolean existsByUsername(String username);
}

4. 创建UserController处理登录和注册逻辑：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
 
@Controller
public class UserController {
 
    @Autowired
    private UserRepository userRepository;
 
    @PostMapping("/register")
    public String registerUser(@RequestParam String username, @RequestParam String password) {
        if (userRepository.existsByUsername(username)) {
            return "register?error";
        }
        User user = new User();
        user.setUsername(username);
        user.setPassword(password);
        userRepository.save(user);
        return "redirect:/login";
    }
 
    @PostMapping("/login")
    public String loginUser(@RequestParam String username, @RequestParam String password, Model model) {
        // 这里简单起见，不进行密码散列比对
        User user = userRepository.findByUsername(username);
        if (user == null || !user.getPassword().equals(password)) {
            model.addAttribute("error", "用户名或密码错误");
            return "login";