SpringMVC归纳-2(Session会话、拦截器)

　　要点：

　　1.HttpSession：一个session的建立是从一个用户向服务器发第一个请求开始，而以用户显式结束或session超时为结束，借助session能在一定时间内记录用户状态。

　　2.ModelAndView：既可以设置URL地址，又可以渲染视图。

　　3.HandlerInterceptor：拦截器接口，通过实现改接口的三个方法（preHandle、postHandle、afterCompletion）可以自定义一个拦截器。

　　实例：

　　实现登录、购物车功能。

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>乐淘登录</title>
</head>
<body>
    <form action="http://localhost:8888/login-commit" method="post">
        <input type="submit" value="login">
    </form>
</body>
</html>

　　mall.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>乐淘商场</title>
</head>
<body>
    <form action="http://localhost:8888/shopcar" method="POST">
        <label>请选择要购买的书籍：<br>
            <input type="checkbox" name="bookname" value="C Prime Plus">C Prime Plus<br>
            <input type="checkbox" name="bookname" value="C Prime Plus2">C Prime Plus2<br>
            <input type="checkbox" name="bookname" value="C Prime Plus3">C Prime Plus3<br>
            <input type="checkbox" name="bookname" value="C Prime Plus4">C Prime Plus4<br>
        </label>
        <input type="submit" value="加入购物车">
    </form>
    <form action="http://localhost:8888/quit" method="POST">
        <input value="log out" type="submit">
    </form>
</body>
</html>

　　myshoppingcar.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>乐淘购物车</title>
</head>
<body>

    <h2>我的购物车：</h2>
    <!--存在购买时显示已购书籍-->
    <ul th:if="${books.size()} != 0">
        <li th:each="bookcount:${books}" th:text="${bookcount}"></li>
    </ul>
    <!--无购买-->
    <div th:if="${books.size()} == 0">
        您未购买任何书籍！        
    </div>
    <form action="http://localhost:8888/mall" method="GET">
        <input type="submit" value="继续购买">
    </form>
    
</body>
</html>

　　Books.java

package com.example.demo.controller.login;

import java.util.HashMap;
import java.util.Map.Entry;
import java.util.Set;

public class Books {
    
    private HashMap<String,Integer> books = new HashMap<String,Integer>(); 
    
    //根据请求URL中获得的表单数组，更新已有书本
    public void refreshBooks(String[] newbooks) {
        
        for (String book:newbooks) {
            
            if (books.containsKey(book)) {
                books.put(book, books.get(book)+1);
            }else {
                books.put(book, 1);
            }
        }
    }
    
    //获取books集合，送往页面
    public Set<Entry<String, Integer>> getbooks(){
        return books.entrySet();
    }
}

　　LoginController.java

package com.example.demo.controller.login;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;

@Controller
public class LoginController {
    
    //登录界面
    @GetMapping("login")
    public String getLogin(HttpServletRequest req) {
        HttpSession session = req.getSession();
        
        //已登录直接进入到商场
        if (session.getAttribute("login")!=null) {
            return "redirect:mall";
        }
        
        return "login";
    }
    
    //登录请求处理
    @PostMapping("login-commit")
    public String postLogin(HttpServletRequest req) {
        HttpSession session = req.getSession();
        
        //session标记登录状态
        session.setAttribute("login",true);
        
        return "redirect:mall";
    }
    
    //退出登录，保留购物记录
    @PostMapping("quit")
    public String quit(HttpServletRequest req) {
        HttpSession session = req.getSession();
        
        session.removeAttribute("login");
        
        return "redirect:login";
    }
    
}

　　ShoppingController.java

package com.example.demo.controller.login;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.servlet.ModelAndView;

@Controller
public class ShoppingController {
    
    //商场
    @GetMapping("mall")
    public String getMall() {
        return "mall";
    }
    
    //我的购物车
    @PostMapping("shopcar")
    public ModelAndView getShopCar(ModelAndView view,HttpServletRequest req) {
        
        HttpSession session = req.getSession();
        Books books = (Books) session.getAttribute("shopcar");//session会话获取已购书籍
        String[] newbooks = req.getParameterValues("bookname");//新的购物请求
        
        //从未购买
        if (books==null){
            books = new Books();
        }
        
        //刷新session会话
        if (newbooks!=null) {
            books.refreshBooks(newbooks);    
            session.setAttribute("shopcar", books);
        }
        
        //刷新model，渲染视图
        view.addObject("books",books.getbooks());
        view.setViewName("myshoppingcar");
        
        return view;
    }
}

　　LoginInterceptor.java

package com.example.demo.controller.login;

import java.io.IOException;

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

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


//登录拦截器
public class LoginInterceptor implements HandlerInterceptor {
    
    @Override
    //在Controller方法之前调用
    public boolean preHandle(HttpServletRequest req,HttpServletResponse res,Object handler) throws IOException {
        
        HttpSession session = req.getSession();
        
        if (session.getAttribute("login") != null) {
            System.out.println("login!");
            return true;
        }
        
        res.sendRedirect("login");
        return false;
    }
    
    @Override
    public void postHandle(HttpServletRequest req,HttpServletResponse res,Object handler,ModelAndView modelandview) throws Exception {
        //Controller方法处理完，但html页面并未送出显示时调用
    }
    
    @Override
    public void afterCompletion(HttpServletRequest req,HttpServletResponse res,Object handler,Exception ex) {
        //页面渲染完毕后调用，通常用来回收资源，类似于finally
    }
    
    
}

　　SpringWebConfig.java

package com.example.demo.controller.login;

import org.springframework.boot.SpringBootConfiguration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@SpringBootConfiguration
public class SpringWebConfig  implements WebMvcConfigurer{
    
    //增加拦截器，可以对特定URL设定拦截以检查是否登录
    public void addInterceptors(InterceptorRegistry registry) {
        
        //装载一个拦截器,可以使用通配符，或字符串数组
        registry.addInterceptor(new LoginInterceptor()).addPathPatterns("/mall","/quit");    
    }

}