拦截器的实现和简单原—ssm&&springboot

目录

原理大概:

 自定义拦截器-SSM

  自定义拦截器—springboot


原理大概:

 核心方法是DispatcherServerlet中的doDispatcher():

//1.
mapperHandler=getHandler(processedRequest);


//2.
HandlerAdapter ha=getHandlerAdapter(mapperedHandler.getHandler());

首先通过getHandler()方法,找到handler(也就是controller下对应的方法),并且会返回一个HandlerExcutionChain执行链,HandlerExcutionChain中有handler以及拦截器interceptor的信息;

然后我们通过getHandlerAdapter()方法找到合适的处理器适配器;

在执行handle()方法之前我们先执行HandlerExcutionChain中的拦截器

 if (!mappedHandler.applyPreHandle(processedRequest, response)) {
    					return;
    				}

按顺序执行所有拦截器的preHandle()方法,如果拦截器preHandle()方法返回为true,则执行下一个拦截器的preHandle,若为false,则倒序执行已经执行了的拦截器的postHandle()方法,若出现异常则触发afterCompletion;

拦截器的实现和简单原—ssm&&springboot

 最后处理适配器,执行handler,返回ModelAndView:

 mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

 自定义拦截器-SSM

<!--配置拦截器-->
<mvc:interceptors>
   <bean class="com.wyh.web.HandlerInterceptor1"></bean>
   <bean class="com.wyh.web.HandlerInterceptor2"></bean>
</mvc:interceptors>

  具体:

<mvc:interceptors>
   <!--拦截所有-->
   <bean class="com.wyh.web.Interceptor1"></bean>
   <mvc:interceptor>
      <!--拦截路径-->
      <mvc:mapping path="/users"/>
  <bean class="com.wyh.web.Interceptor2"></bean>
   </mvc:interceptor>
</mvc:interceptors>

eg:

package com.yanzhen.utils;

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class PathInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String path = request.getContextPath();
        String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
        request.setAttribute("basePath",basePath);
        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 {

    }
}
 <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/**/*"/>
            <bean class="com.yanzhen.utils.PathInterceptor" />
        </mvc:interceptor>
        <mvc:interceptor>
            <mvc:mapping path="/**/*"/>
            <mvc:exclude-mapping path="/login"/>
            <mvc:exclude-mapping path="/logout"/>
<!--            这里是/captcha/*是因为后面只有一个子路径了-->
            <mvc:exclude-mapping path="/captcha/*"/>
<!--            后面还有多个文件-->
            <mvc:exclude-mapping path="/static/**"/>
            <bean class="com.yanzhen.utils.PermissionInterceptor"/>
        </mvc:interceptor>
    </mvc:interceptors>

  自定义拦截器—springboot

   首先需要明确自定义的拦截器需要放到容器中的:

   1.首先自定义一个config类,实现WebMvcConfigurer;

   然后重写里面的方法,将自定义的拦截器注册到容器中,并且实现addPathPatterns("/**"),所     有请求被拦截,然后指定放行掉的路径资源 .excludePathPattens("/xxx/xxx");

 

package com.atguigu.admin.config;

/**
 * 1、编写一个拦截器实现HandlerInterceptor接口
 * 2、拦截器注册到容器中(实现WebMvcConfigurer的addInterceptors)
 * 3、指定拦截规则【如果是拦截所有,静态资源也会被拦截】
 *
 * @EnableWebMvc:全面接管
 *      1、静态资源?视图解析器?欢迎页.....全部失效
 */
//@EnableWebMvc
@Configuration
public class AdminWebConfig implements WebMvcConfigurer{


    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoginInterceptor())
                .addPathPatterns("/**")  //所有请求都被拦截包括静态资源
                .excludePathPatterns("/","/login","/css/**","/fonts/**","/images/**",
                        "/js/**","/aa/**"); //放行的请求

}

   2.自定义拦截器:实现HandlerInterceptor接口,重写preHandle()、PostHandle()、                   afterCompletion() ;

package com.atguigu.admin.interceptor;

/**
 * 登录检查
 * 1、配置好拦截器要拦截哪些请求
 * 2、把这些配置放在容器中
 */
@Slf4j
public class LoginInterceptor implements HandlerInterceptor {

    /**
     * 目标方法执行之前
     * @param request
     * @param response
     * @param handler
     * @return
     * @throws Exception
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {

        String requestURI = request.getRequestURI();
        log.info("preHandle拦截的请求路径是{}",requestURI);

        //登录检查逻辑
        HttpSession session = request.getSession();

        Object loginUser = session.getAttribute("loginUser");

        if(loginUser != null){
            //放行
            return true;
        }

        //拦截住。未登录。跳转到登录页,不用response.setAttribute()
//        resp.sendRedirect()不能显示提示信息msg的原因就是:重定向已经是服务器重新响应到登录页面上,此时没有操作,固然不会显示msg
//        而请求转发,是请求域中放了msg,所以说前端可以取到请求域中的内容
        request.setAttribute("msg","请先登录");
//        re.sendRedirect("/");
        request.getRequestDispatcher("/").forward(request,response);
        return false;
    }

    /**
     * 目标方法执行完成以后
     * @param request
     * @param response
     * @param handler
     * @param modelAndView
     * @throws Exception
     */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        log.info("postHandle执行{}",modelAndView);
    }

    /**
     * 页面渲染以后
     * @param request
     * @param response
     * @param handler
     * @param ex
     * @throws Exception
     */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        log.info("afterCompletion执行异常{}",ex);
    }
}

注意:如果任何一个拦截器返回false,直接跳出不执行该目标方法,且倒序执行返回为true的拦截器的postHandle()方法(作用于方法执行完后与视图层阶段),如果出现异常就会触发afterCompletion()方法,就算页面成功渲染也一样会倒序触发这个方法;

   

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