Day33——登录&拦截器

我会带着你远行 2023-02-24 08:58 53阅读 0赞

### 文章目录 ###

*  一. 回顾
 *  二. 需求
 *  三. 代码
 *  四. 效果展示
 *  五. 踩坑要点
 *   *  5.1 修改html页面代码无效
     *  5.2 静态资源加载失败
     *  5.3 登录成功后跳转失败

# 一. 回顾 #

昨天讲述[Day32——国际化][Day32]，今天学习登录&拦截器

# 二. 需求 #

访问登录页面，输入用户名以及密码点击登录，后台验证密码是否正确，若正确则由登录页面进入到主页面。

# 三. 代码 #

首先修改登录页面的form表单提交地址`th:action="@{/user/login}"`，提交方式注意是post方式，如下：

然后写一个controller方法，控制跳转，如下：

package com.atguigu.springboot.controller;
    
    import org.springframework.stereotype.Controller;
    import org.springframework.web.bind.annotation.PostMapping;
    import org.springframework.web.bind.annotation.RequestParam;
    import org.thymeleaf.util.StringUtils;
    
    import javax.servlet.http.HttpSession;
    import java.util.Map;
    
    /** * 登录控制器 */
    @Controller
    public class LoginController { 
    
        @PostMapping(value = "/user/login")
        public String login(@RequestParam("username")String username,
                            @RequestParam("password")String password,
                            Map<String, Object> map, HttpSession session){ 
            if(!StringUtils.isEmpty(username) && "123456".equals(password)){ 
                System.out.println("dashboard");
                session.setAttribute("loginUser", username);//保存登录状态，用来判断是否要拦截请求
                //防止表单重复提交，重定向到主页
                return "redirect:/main.html";
            }else{ 
                map.put("msg", "用户名密码错误");
                return "login";
            }
    
        }
    }

在登录页面添加错误信息展示代码，如下：

<p style="color: red" th:text="${msg}" th:if="${not #strings.isEmpty(msg)}" ></p>

定义视图映射，如果登录成功则重定向到main.html（main.html定义视图映射到dashboard.html），如下：

package com.atguigu.springboot.config;
    
    @Configuration
    //@EnableWebMvc
    public class MyMvcConfig2 implements WebMvcConfigurer { 
    
    
    
        /** * 所有的WebMvcConfigurer都会一起起作用 * @return */
        @Bean //将组件加载进容器中
        public WebMvcConfigurer webMvcConfigurer() { 
            return new WebMvcConfigurer() { 
                @Override
                public void addViewControllers(ViewControllerRegistry registry) { 
                    registry.addViewController("/").setViewName("login");
                    registry.addViewController("/index.html").setViewName("login");
                    registry.addViewController("/main.html").setViewName("dashboard");
    
                }          
    }

定义登录拦截器，如下：

package com.atguigu.springboot.component;
    
    import org.springframework.web.servlet.HandlerInterceptor;
    import org.springframework.web.servlet.ModelAndView;
    
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    /** * 登录检查 */
    public class LoginHandlerInterceptor implements HandlerInterceptor { 
        //目标方法执行之前
        @Override
        public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { 
            Object user = request.getSession().getAttribute("loginUser");
            if(user == null){ 
                //未登录
                request.setAttribute("msg", "没有权限请先登录");
                request.getRequestDispatcher("/index.html").forward(request, response);
                return false;
            }else{ 
                //已登录,放行
                return true;
            }
        }
    
        @Override
        public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception { 
    
        }
    
        @Override
        public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception { 
    
        }
    }

注册拦截器，如下：

package com.atguigu.springboot.config;
    
    @Configuration
    //@EnableWebMvc
    public class MyMvcConfig2 implements WebMvcConfigurer { 
      
    
        /** * 所有的WebMvcConfigurer都会一起起作用 * @return */
        @Bean //将组件加载进容器中
        public WebMvcConfigurer webMvcConfigurer() { 
            return new WebMvcConfigurer() { 
               
                //注册拦截器
                @Override
                public void addInterceptors(InterceptorRegistry registry) { 
                    registry.addInterceptor(new LoginHandlerInterceptor()).addPathPatterns("/**")
                            .excludePathPatterns("/asserts/**", "/webjars/**",
                                    "/", "/index.html", "/user/login");
                }
            };
        }
    
    }

在dashboard.html页面设置用户名在左上角显示，如下:

<a class="navbar-brand col-sm-3 col-md-2 mr-0" href="http://getbootstrap.com/docs/4.0/examples/dashboard/#">
              [[ ${session.loginUser} ]]</a>

# 四. 效果展示 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNjM0ODQ2_size_16_color_FFFFFF_t_70]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNjM0ODQ2_size_16_color_FFFFFF_t_70 1]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNjM0ODQ2_size_16_color_FFFFFF_t_70 2]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNjM0ODQ2_size_16_color_FFFFFF_t_70 3]

# 五. 踩坑要点 #

按照上面代码运行如果报错的话，常见有下面2种错误情况。笔者亲自遇到并解决

## 5.1 修改html页面代码无效 ##

*  首先在application.properties配置`spring.thymeleaf.cache=false`禁用thymeleaf的缓存功能
 *  修改完html代码后，按ctrl+F9编译文件。或者设置idea自动编译，如下：  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNjM0ODQ2_size_16_color_FFFFFF_t_70 4]

## 5.2 静态资源加载失败 ##

[关于thymeleaf静态资源引用无效][thymeleaf]

## 5.3 登录成功后跳转失败 ##

[Error resolving template \[dashboard\], template might not exist or might not be acceible][Error resolving template _dashboard_ template might not exist or might not be acceible]

[Day32]: https://blog.csdn.net/qq_40634846/article/details/107202693
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNjM0ODQ2_size_16_color_FFFFFF_t_70 1]: /images/20230209/d6c6560634ce41338b300e50770223b6.png
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNjM0ODQ2_size_16_color_FFFFFF_t_70 4]: https://img-blog.csdnimg.cn/2020070918420693.jpg?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNjM0ODQ2,size_16,color_FFFFFF,t_70
[thymeleaf]: https://blog.csdn.net/qq_40634846/article/details/107228001
[Error resolving template _dashboard_ template might not exist or might not be acceible]: https://blog.csdn.net/qq_40634846/article/details/107235093