SpringMVC框架六：拦截器

时间：2023-03-09 19:15:22
SpringMVC框架六：拦截器

拦截器的概念就不介绍了：

SpringMVC中拦截器的执行规则：

一个小示例展示：

我搞两个拦截器：

第一个：

package org.dreamtech.springmvc.interceptor;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.HandlerInterceptor;

import org.springframework.web.servlet.ModelAndView;

public class Interceptor1 implements HandlerInterceptor {

    @Override

    public void afterCompletion(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2, Exception arg3)

            throws Exception {

        System.out.println("页面渲染后1");

    }

    @Override

    public void postHandle(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2, ModelAndView arg3)

            throws Exception {

        System.out.println("方法后1");

    }

    @Override

    public boolean preHandle(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2) throws Exception {

        System.out.println("方法前1");

        return true;

    }

}

第二个：

package org.dreamtech.springmvc.interceptor;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.HandlerInterceptor;

import org.springframework.web.servlet.ModelAndView;

public class Interceptor2 implements HandlerInterceptor {

    @Override

    public void afterCompletion(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2, Exception arg3)

            throws Exception {

        System.out.println("页面渲染后2");

    }

    @Override

    public void postHandle(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2, ModelAndView arg3)

            throws Exception {

        System.out.println("方法后2");

    }

    @Override

    public boolean preHandle(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2) throws Exception {

        System.out.println("方法前2");

        return true;

    }

}

然后把它配置到SpringMVC.xml中：

    <!-- 配置拦截器 -->

    <mvc:interceptors>

        <!-- 配置多个拦截器 -->

        <mvc:interceptor>

            <!-- 拦截所有 -->

            <mvc:mapping path="/**" />

            <!-- 自定义拦截器类 -->

            <bean class="org.dreamtech.springmvc.interceptor.Interceptor1" />

        </mvc:interceptor>

        <mvc:interceptor>

            <!-- 拦截所有 -->

            <mvc:mapping path="/**" />

            <!-- 自定义拦截器类 -->

            <bean class="org.dreamtech.springmvc.interceptor.Interceptor2s" />

        </mvc:interceptor>

    </mvc:interceptors>

执行之后：

SpringMVC框架六：拦截器

然而我们如果把拦截器一的方法前不放行：

    @Override

    public boolean preHandle(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2) throws Exception {

        System.out.println("方法前1");

        return false;

    }

这时候，发现控制台只是打印了：方法前1

但是，我们如果把拦截器二的方法前不放行：

打印的却是：

SpringMVC框架六：拦截器

到这里就可以看出SpringMVC的执行规则了：

为了方便，我借用某博主的图片:

SpringMVC框架六：拦截器

文字解释：

preHandler按拦截器定义顺序调用，

postHandler按拦截器定义逆序调用，

afterCompletion按拦截器定义逆序调用，

postHandler在所有的拦截器返回成功时候才会调用，

afterCompletion在preHandler返回true才会调用

应用：

登录功能：只有登录才能查看其他信息

限制：在非登陆状态下无法访问该网站任何一处

随意写一个登录页面：

<body>

    <form action="${pageContext.request.contextPath }/login.action" method="post">

        用户名：<input type="text" name="username"> 
               <input type="submit" value="提交">

    </form>

</body>

只用一个拦截器：

    <mvc:interceptors>

        <mvc:interceptor>

            <mvc:mapping path="/**" />

            <bean class="org.dreamtech.springmvc.interceptor.Interceptor2" />

        </mvc:interceptor>

    </mvc:interceptors>

拦截器：

package org.dreamtech.springmvc.interceptor;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.HandlerInterceptor;

import org.springframework.web.servlet.ModelAndView;

public class Interceptor2 implements HandlerInterceptor {

    @Override

    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object arg2, Exception arg3)

            throws Exception {

    }

    @Override

    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object arg2, ModelAndView arg3)

            throws Exception {

    }

    @Override

    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object arg2) throws Exception {

        String requestURI = request.getRequestURI();

        /*

         * URI:/login.action

         * URL:http://xxx/xxx/login.action

         */

        if(!requestURI.contains("/login")){

            String username = (String) request.getSession().getAttribute("USER_SESSION");

            if(username==null){

                response.sendRedirect(request.getContextPath()+"/login.action");

                return false;

            }

        }

        return true;

    }

}

实现：

    @RequestMapping(value = "/login.action", method = RequestMethod.GET)

    public String login() {

        return "login";

    }

    @RequestMapping(value = "/login.action", method = RequestMethod.POST)

    public String login(String username, HttpSession httpSession) {

        httpSession.setAttribute("USER_SESSION", username);

        return "redirect:/item/itemlist.action";

    }

这里注意：我直接返回字符串：login是因为提前做了配置：

    <bean

        class="org.springframework.web.servlet.view.InternalResourceViewResolver">

        <property name="prefix" value="/WEB-INF/jsp/" />

        <property name="suffix" value=".jsp" />

    </bean>

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