[数据结构与算法]springmvc的拦截器

作用：当用户访问某个资源时，我们需要做一些判断，若满足条件，让用户访问资源，若不满足，则跳转到指定页面！

那如何实现呢？

首先新建一个类让其实现HandlerInterceptor，重写方法，在第一个重写的方法也就是

public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws ServletException, IOException 里面做一些判断。满足条件用户可以访问资源，不满足，用户跳转到指定资源。

然后在applicationcontext.xml添加拦截路径，比如：

    <!--关于拦截器的配置-->
    <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/management/**"/>
            <bean id="拦截器名字" class="拦截器具体路径"/>
        </mvc:interceptor>
    </mvc:interceptors>
</beans>

来个具体的代码吧:

package com.imooc.reader.interceptor;

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

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class LoginInterceptor implements HandlerInterceptor {

    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws ServletException, IOException {
        // 如果是登陆页面则放行

        if (request.getRequestURI().contains("login")) {
            return true;
        }

        HttpSession session = request.getSession();

        // 如果用户已登陆也放行
        if(session.getAttribute("user") != null) {
            return true;
        }

        // 用户没有登陆跳转到登陆页面
        request.getRequestDispatcher("/WEB-INF/ftl/management/login.ftl").forward(request, response);
        return false;
    }

    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {

    }

    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {

    }
}

拦截路径

    <!--关于拦截器的配置-->
    <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/management/**"/>
            <bean id="loginInterceptor" class="com.imooc.reader.interceptor.LoginInterceptor"/>
        </mvc:interceptor>
    </mvc:interceptors>

备注一下下，复习个小知识点：获取当前访问时候的uri；

request.getRequestURI()

ok，实现了动态拦截！！！！