我需要基于Java实现

好的，以下是一个基于Java的实现示例：

1. 首先需要添加以下依赖到你的项目中：

<dependency>
    <groupId>org.springframework.security.oauth</groupId>
    <artifactId>spring-security-oauth2</artifactId>
    <version>2.3.7.RELEASE</version>
</dependency>

2. 在你的Spring Boot应用程序中，创建一个OAuth2客户端配置类，用于配置OAuth2客户端的基本信息，例如客户端ID、密钥、授权服务器地址等等。下面是一个示例：

@Configuration
@EnableOAuth2Client
public class OAuth2ClientConfiguration {

    @Value("${oauth2.client.client-id}")
    private String clientId;

    @Value("${oauth2.client.client-secret}")
    private String clientSecret;

    @Value("${oauth2.client.access-token-uri}")
    private String accessTokenUri;

    @Value("${oauth2.client.user-authorization-uri}")
    private String userAuthorizationUri;

    @Value("${oauth2.client.redirect-uri}")
    private String redirectUri;

    @Bean
    public OAuth2ProtectedResourceDetails oauth2ProtectedResourceDetails() {
        ClientCredentialsResourceDetails resourceDetails = new ClientCredentialsResourceDetails();
        resourceDetails.setClientId(clientId);
        resourceDetails.setClientSecret(clientSecret);
        resourceDetails.setAccessTokenUri(accessTokenUri);
        resourceDetails.setUserAuthorizationUri(userAuthorizationUri);
        resourceDetails.setScope(Arrays.asList("read", "write"));
        return resourceDetails;
    }

    @Bean
    public OAuth2RestTemplate oauth2RestTemplate(OAuth2ClientContext oauth2ClientContext) {
        return new OAuth2RestTemplate(oauth2ProtectedResourceDetails(), oauth2ClientContext);
    }

    @Bean
    public OAuth2ClientContext oauth2ClientContext() {
        return new DefaultOAuth2ClientContext(new DefaultAccessTokenRequest());
    }

    @Bean
    public FilterRegistrationBean oauth2ClientFilterRegistration(OAuth2ClientContextFilter filter) {
        FilterRegistrationBean registration = new FilterRegistrationBean();
        registration.setFilter(filter);
        registration.setOrder(-100);
        return registration;
    }

    @Bean
    public AuthorizationCodeResourceDetails authorizationCodeResourceDetails() {
        AuthorizationCodeResourceDetails resourceDetails = new AuthorizationCodeResourceDetails();
        resourceDetails.setClientId(clientId);
        resourceDetails.setClientSecret(clientSecret);
        resourceDetails.setAccessTokenUri(accessTokenUri);
        resourceDetails.setUserAuthorizationUri(userAuthorizationUri);
        resourceDetails.setScope(Arrays.asList("read", "write"));
        resourceDetails.setPreEstablishedRedirectUri(redirectUri);
        resourceDetails.setUseCurrentUri(false);
        return resourceDetails;
    }

    @Bean
    public OAuth2RestTemplate oauth2RestTemplate(AuthorizationCodeResourceDetails resourceDetails, OAuth2ClientContext oauth2ClientContext) {
        return new OAuth2RestTemplate(resourceDetails, oauth2ClientContext);
    }
}

在上面的配置类中，我们配置了一个OAuth2客户端，它使用密码模式进行授权。我们使用了`ClientCredentialsResourceDetails`类，它提供了客户端ID、密钥、授权服务器地址等基本信息。我们还使用了`OAuth2RestTemplate`类，它用于向授权服务器发送请求，并获取访问令牌。

3. 然后，我们需要创建一个控制器类，用于处理用户登录和访问受保护的资源。下面是一个示例：

@RestController
public class UserController {

    @Autowired
    private OAuth2RestTemplate restTemplate;

    @GetMapping("/login")
    public String login() {
        return "Please log in";
    }

    @PostMapping("/login")
    public String login(@RequestParam String username, @RequestParam String password, HttpServletRequest request) {
        // 使用密码模式进行授权
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
        MultiValueMap<String, String> map = new LinkedMultiValueMap<>();
        map.add("grant_type", "password");
        map.add("client_id", "myClientId");
        map.add("client_secret", "myClientSecret");
        map.add("username", username);
        map.add("password", password);
        HttpEntity<MultiValueMap<String, String>> entity = new HttpEntity<>(map, headers);
        ResponseEntity<Map> response = restTemplate.postForEntity("/oauth/token", entity, Map.class);
        if (response.getStatusCode() == HttpStatus.OK) {
            // 将访问令牌存储在会话中
            request.getSession().setAttribute("access_token", response.getBody().get("access_token"));
            return "Logged in successfully";
        } else {
            return "Invalid username or password";
        }
    }

    @GetMapping("/dashboard")
    public String dashboard(HttpServletRequest request) {
        // 检查访问令牌是否存在
        String accessToken = (String) request.getSession().getAttribute("access_token");
        if (accessToken == null) {
            return "Please log in";
        } else {
            // 向受保护的资源发送请求
            HttpHeaders headers = new HttpHeaders();
            headers.setBearerAuth(accessToken);
            HttpEntity<String> entity = new HttpEntity<>(headers);
            ResponseEntity<Map> response = restTemplate.exchange("/api/resource", HttpMethod.GET, entity, Map.class);
            if (response.getStatusCode() == HttpStatus.OK) {
                return "Hello, " + response.getBody().get("username") + "!";
            } else {
                return "Unauthorized";
            }
        }
    }
}

在上面的控制器类中，我们处理了登录请求和访问受保护的资源请求。我们使用了`OAuth2RestTemplate`类向授权服务器发送请求，并获取访问令牌。在登录请求中，我们向授权服务器发送了用户名和密码，以获取访问令牌。如果访问令牌有效，则将其存储在会话中。在访问受保护的资源请求中，我们检查访问令牌是否存在，并向受保护的资源发送请求。