digdeep

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在项目中遇到一个问题,在 Filter中注入 Serivce失败,注入的service始终为null。如下所示:

public class WeiXinFilter implements Filter{
    
    @Autowired
    private UsersService usersService;

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest)request;
        HttpServletResponse resp = (HttpServletResponse)response;
     Users users = this.usersService.queryByOpenid(openid);
}

上面的 usersService 会报空指针异常。

解决方法一

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest)request;
        HttpServletResponse resp = (HttpServletResponse)response;
        ServletContext sc = req.getSession().getServletContext();
        XmlWebApplicationContext cxt = (XmlWebApplicationContext)WebApplicationContextUtils.getWebApplicationContext(sc);
        
        if(cxt != null && cxt.getBean("usersService") != null && usersService == null)
            usersService = (UsersService) cxt.getBean("usersService");
        
        Users users = this.usersService.queryByOpenid(openid);

这样就行了。

方法二

public class WeiXinFilter implements Filter{
    
    private UsersService usersService;
    
    public void init(FilterConfig fConfig) throws ServletException {
        ServletContext sc = fConfig.getServletContext(); 
        XmlWebApplicationContext cxt = (XmlWebApplicationContext)WebApplicationContextUtils.getWebApplicationContext(sc);
        
        if(cxt != null && cxt.getBean("usersService") != null && usersService == null)
            usersService = (UsersService) cxt.getBean("usersService");        
    }

相关原理

1. 如何获取 ServletContext

1)在javax.servlet.Filter中直接获取
ServletContext context = config.getServletContext();

2)在HttpServlet中直接获取
this.getServletContext()

3)在其他方法中,通过HttpServletRequest获得
request.getSession().getServletContext();

2. WebApplicationContext 与 ServletContext (转自:http://blessht.iteye.com/blog/2121845):

Spring的 ContextLoaderListener是一个实现了ServletContextListener接口的监听器,在启动项目时会触发contextInitialized方法(该方法主要完成ApplicationContext对象的创建),在关闭项目时会触发contextDestroyed方法(该方法会执行ApplicationContext清理操作)。

ConextLoaderListener加载Spring上下文的过程

①启动项目时触发contextInitialized方法,该方法就做一件事:通过父类contextLoader的initWebApplicationContext方法创建Spring上下文对象。

②initWebApplicationContext方法做了三件事:创建 WebApplicationContext;加载对应的Spring文件创建里面的Bean实例;将WebApplicationContext放入 ServletContext(就是Java Web的全局变量)中

③createWebApplicationContext创建上下文对象,支持用户自定义的上下文对象,但必须继承自ConfigurableWebApplicationContext,而Spring MVC默认使用ConfigurableWebApplicationContext作为ApplicationContext(它仅仅是一个接口)的实 现。

④configureAndRefreshWebApplicationContext方法用 于封装ApplicationContext数据并且初始化所有相关Bean对象。它会从web.xml中读取名为 contextConfigLocation的配置,这就是spring xml数据源设置,然后放到ApplicationContext中,最后调用传说中的refresh方法执行所有Java对象的创建。

⑤完成ApplicationContext创建之后就是将其放入ServletContext中,注意它存储的key值常量。

方法三

直接使用spring mvc中的HandlerInterceptor或者HandlerInterceptorAdapter 来替换Filter:

public class WeiXinInterceptor implements HandlerInterceptor {
    @Autowired
    private UsersService usersService;   
    
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
            throws Exception {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        // TODO Auto-generated method stub
        
    }
}

配置拦截路径:

    <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/**" />
            <bean class="net.xxxx.interceptor.WeiXinInterceptor" />
        </mvc:interceptor>     
    </mvc:interceptors>

 

Filter 中注入 Service 的示例:

public class WeiXinFilter implements Filter{    
    private UsersService usersService;    
    public void init(FilterConfig fConfig) throws ServletException {}
    public WeiXinFilter() {}
    public void destroy() {}

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest)request;
        HttpServletResponse resp = (HttpServletResponse)response;
        
        String userAgent = req.getHeader("user-agent");
if(userAgent != null && userAgent.toLowerCase().indexOf("micromessenger") != -1){ // 微信浏览器 String servletPath = req.getServletPath(); String requestURL = req.getRequestURL().toString(); String queryString = req.getQueryString(); if(queryString != null){ if(requestURL.indexOf("mtzs.html") !=-1 && queryString.indexOf("LLFlag")!=-1){ req.getSession().setAttribute("LLFlag", "1"); chain.doFilter(request, response); return; } } String openidDES = CookieUtil.getValueByName("openid", req); String openid = null; if(StringUtils.isNotBlank(openidDES)){ try { openid = DesUtil.decrypt(openidDES, "rxxxxxxxxxde"); // 解密获得openid } catch (Exception e) { e.printStackTrace(); } } // ... ... String[] pathArray = {"/weixin/enterAppFromWeiXin.json", "/weixin/getWeiXinUserInfo.json", "/weixin/getAccessTokenAndOpenid.json", "/sendRegCode.json", "/register.json", "/login.json", "/logon.json", "/dump.json", "/queryInfo.json"}; List<String> pathList = Arrays.asList(pathArray); String loginSuccessUrl = req.getParameter("path"); String fullLoginSuccessUrl = "http://www.axxxxxxx.cn/pc/"; if(requestURL.indexOf("weixin_gate.html") != -1){ req.getSession().setAttribute("loginSuccessUrl", loginSuccessUrl);
          // ... ...
}
        ServletContext sc = req.getSession().getServletContext();
XmlWebApplicationContext cxt = (XmlWebApplicationContext)WebApplicationContextUtils.getWebApplicationContext(sc);
        
         if(cxt != null && cxt.getBean("usersService") != null && usersService == null)
            usersService = (UsersService) cxt.getBean("usersService");
        
         Users users = this.usersService.queryByOpenid(openid); // ... ...
if(pathList.contains(servletPath)){ // pathList 中的访问路径直接 pass chain.doFilter(request, response); return; }else{ if(req.getSession().getAttribute(CommonConstants.SESSION_KEY_USER) == null){ // 未登录 String llFlag = (String) req.getSession().getAttribute("LLFlag"); if(llFlag != null && llFlag.equals("1")){ // 处理游客浏览 chain.doFilter(request, response); return; } // ... ...// 3. 从腾讯服务器去获得微信的 openid , req.getRequestDispatcher("/weixin_gate.html").forward(request, response); return; }else{ // 已经登录 // 4. 已经登录时的处理 chain.doFilter(request, response); return; } } }else{ // 非微信浏览器 chain.doFilter(request, response); } } }

 

posted on 2015-08-29 22:43  digdeep  阅读(17077)  评论(3编辑  收藏  举报
不懂数据库和Web安全的架构师不是一个好的程序员。