SpringBoot2学习笔记
四、Web开发
4.7)拦截器
4.7.1)HandlerInterceptor 接口
HandlerInterceptor.java的源码如下:
public interface HandlerInterceptor {
// 目标方法执行之前进行拦截
default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
return true;
}
// 目标方法执行完成以后进行拦截
default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception {
}
// 页面渲染以后进行拦截
default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception {
}
}
在工程SpringBootDemo4Admin中,新建 LoginInterceptor.java,代码如下:
package com.study.admin.interceptor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
/**
* 拦截器
* 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 {
/**
* 目标方法执行之前进行拦截
*
* @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");
// 用户已登录
if (loginUser != null) {
//放行
return true;
}
//拦截住。未登录。跳转到登录页
request.setAttribute("msg", "请先登录");
// 转发至登录页
request.getRequestDispatcher("/").forward(request, response);
return false;
}
/**
* 目标方法执行完成以后进行拦截
*
* @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);
}
/**
* 页面渲染以后进行拦截
*
* @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);
}
}
4.7.2)配置拦截器
新建 AdminWebConfig.java,代码如下:
/**
* 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】
*
*/
@Configuration
public class AdminWebConfig implements WebMvcConfigurer {
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(new LoginInterceptor())
//所有请求都被拦截包括静态资源
.addPathPatterns("/**")
//剔除不被拦截的请求路径,放行的请求
.excludePathPatterns("/", "/login", "/css/**", "/fonts/**", "/images/**",
"/js/**", "/aa/**");
}
}
测试:浏览器访问:http://localhost:8080/main.html,页面如下:
控制台输出:
2022-06-07 20:15:41.569 INFO 22852 --- [nio-8080-exec-3] c.s.admin.interceptor.LoginInterceptor : preHandle拦截的请求路径是/main.html
输入用户和密码,点击登录后,页面重定向至主页,控制台输出:
2022-06-07 20:20:54.747 INFO 22852 --- [nio-8080-exec-7] c.s.admin.interceptor.LoginInterceptor : preHandle拦截的请求路径是/main.html
2022-06-07 20:20:54.748 INFO 22852 --- [nio-8080-exec-7] c.s.admin.controller.IndexController : 当前方法是:mainPage
2022-06-07 20:20:54.748 INFO 22852 --- [nio-8080-exec-7] c.s.admin.interceptor.LoginInterceptor : postHandle执行ModelAndView [view="main"; model={}]
2022-06-07 20:20:54.858 INFO 22852 --- [nio-8080-exec-7] c.s.admin.interceptor.LoginInterceptor : afterCompletion执行异常{}
4.7.3)拦截器原理
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根据当前请求,找到HandlerExecutionChain【可以处理请求的handler以及handler的所有拦截器】源码如下图:
先来顺序执行所有拦截器的 preHandle方法:
-
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如果当前拦截器prehandler返回为true。则执行下一个拦截器的preHandle;
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如果当前拦截器返回为false,直接 倒序执行所有已经执行了的拦截器的 afterCompletion;
-
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如果任何一个拦截器返回false,直接跳出不执行目标方法
-
所有拦截器都返回True。执行目标方法
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倒序执行所有拦截器的postHandle方法
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前面的步骤有任何异常都会直接倒序触发 afterCompletion
-
页面成功渲染完成以后,也会倒序触发 afterCompletion
拦截器的执行流程如下图: