在Java filter中调用service层方法

最新推荐文章于 2024-09-25 09:20:30 发布

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#java #spring

本文探讨了在Spring Web应用中，Filter中Autowired注解注入Service失败的问题，提供了三种解决方法，包括使用WebApplicationContext、避免懒加载和使用HandlerInterceptor。还介绍了Spring ContextLoaderListener的工作原理和如何正确使用不同场景下的ServletContext获取方式。

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);

解决方法二：

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");        
    }

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：

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();

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。

解决方法三：

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);
        }
    }
 
}