将登录等信息保存到session中和退出session

JShop简介：jshop是一套使用Java语言开发的B2C网店系统，致力于为个人和中小企业提供免费、好用的网店系统。

项目主页：http://git.oschina.net/dinguangx/jshop

在线演示：

• 前台: http://jshop.ofmall.org:81/jshop
• 后台: http://jshop.ofmall.org:81/jshop/manage/user/login (admin/123456)

在spring mvc中，为了随时都能取到当前请求的request对象，可以通过RequestContextHolder的静态方法getRequestAttributes()获取Request相关的变量，如request, response等。 
        在jshop中，对RequestContextHolder的使用进一步封装，简化为RequestHolder类，如下：

public class RequestHolder {

    public static HttpServletRequest getRequest(){

        HttpServletRequest req = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();

        return req;

    }

<span class="hljs-keyword">public <span class="hljs-keyword">static HttpServletResponse <span class="hljs-title">getResponse(){</br>
    HttpServletResponse resp = ((ServletWebRequest)RequestContextHolder.getRequestAttributes()).getResponse();</br>
    <span class="hljs-keyword">return resp;</br>
}</br></br>

}

在大部分的情况下，它都能很好地工作，但在商品管理编辑中，新增商品时，却出现了意外的问题：通过RequestHolder.getRequest().getParameter()得不到参数值，通过debug发现，
通过spring mvc的method注入的request对象实际为MultipartHttpServletRequest,而通过RequestHolder.getRequest()获取到的request对象却是org.apache.catalina.connector.RequestFacade的实例。

public class RequestFacade implements 
HttpServletRequest 

原来在商品新增时，由于使用了文件上传，form表单的enctype类型为”multipart/form-data”，
spring mvc对文件上传的处理类实际却为spring-mvc.xml文件中配置的CommonsMultipartResolver，
该类先判断当前请求是否为multipart类型，如果是的话，将request对象转为MultipartHttpServletRequet,相关的源码见DisptcherServlet

    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {

        HttpServletRequest processedRequest = request;

        ......
                processedRequest = checkMultipart(request);

                multipartRequestParsed = processedRequest != request;


        ......
                // Actually invoke the handler.

                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

        ......
    }
<span class="hljs-keyword">protected HttpServletRequest <span class="hljs-title"><span style="color: #ff0000; font-size: 14pt;"><strong>checkMultipart</strong></span>(HttpServletRequest request) <span class="hljs-keyword">throws MultipartException {</br>
    <span class="hljs-keyword">if (<span class="hljs-keyword">this.multipartResolver != <span class="hljs-keyword">null &amp;&amp; <span class="hljs-keyword">this.multipartResolver.isMultipart(request)) {</br>
        <span class="hljs-keyword">if (request <span class="hljs-keyword"><span style="color: #ff0000; font-size: 14pt;"><strong>instanceof MultipartHttpServletRequest</strong></span>) {</br>
            logger.debug(<span class="hljs-string">"Request is already a MultipartHttpServletRequest - if <span style="color: #0000ff; font-size: 18pt;"><strong>not in a forward</strong></span>, " +</br>
                    <span class="hljs-string">"this typically results from an additional MultipartFilter in web.xml");</br>
        }</br>
        <span class="hljs-keyword">else {</br>
            <span class="hljs-keyword">return <span class="hljs-keyword">this.multipartResolver.<span style="color: #0000ff; font-size: 14pt;"><strong>resolveMultipart</strong></span>(request);</br>
        }</br>
    }</br>
    <span class="hljs-comment">// If not returned before: return original request.</br>
    <span class="hljs-keyword">return request;</br>
}</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code></pre>

那么，RequestContextHolder中的request又是从哪来的呢？ 
继续翻看DispatcherServlet的源码，从其父类FrameworkServlet中找到的processRequest()以相关方法源码：

    protected final void processRequest(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {


        ......
    RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();</br>
    ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);</br></br>

    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);</br>
    asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), <span class="hljs-keyword">new RequestBindingInterceptor());</br></br>

    initContextHolders(request, localeContext, requestAttributes);</br></br>

    <span class="hljs-keyword">try {</br>
        doService(request, response);</br>
    }</br>
    ......</br>
}</br>

<span class="hljs-keyword">protected ServletRequestAttributes <span class="hljs-title"><span style="color: #ff0000; font-size: 14pt;"><strong>buildRequestAttributes</strong></span>(</br>
        HttpServletRequest request, HttpServletResponse response, RequestAttributes previousAttributes) {</br></br>

    <span class="hljs-keyword">if (previousAttributes == <span class="hljs-keyword">null || previousAttributes <span class="hljs-keyword"><span style="color: #ff0000; font-size: 14pt;"><strong>instanceof ServletRequestAttributes</strong></span>) {</br></br>
        <span class="hljs-keyword">return <span class="hljs-keyword">new ServletRequestAttributes(request);
    }</br>
    <span class="hljs-keyword">else {</br>
        <span class="hljs-keyword">return <span class="hljs-keyword">null;  <span class="hljs-comment">// preserve the pre-bound RequestAttributes instance</br>
    }</br>
}</br></br>

<span class="hljs-keyword">private <span class="hljs-keyword">void <span class="hljs-title">initContextHolders(</br>
        HttpServletRequest request, LocaleContext localeContext, RequestAttributes requestAttributes) {</br></br>

    <span class="hljs-keyword">if (localeContext != <span class="hljs-keyword">null) {</br>
        LocaleContextHolder.setLocaleContext(localeContext, <span class="hljs-keyword">this.threadContextInheritable);</br>
    }</br>
    <span class="hljs-keyword">if (requestAttributes != <span class="hljs-keyword">null) {</br>
        RequestContextHolder.setRequestAttributes(requestAttributes, <span class="hljs-keyword">this.threadContextInheritable);</br>
    }</br>
    <span class="hljs-keyword">if (logger.isTraceEnabled()) {</br>
        logger.trace(<span class="hljs-string">"Bound request context to thread: " + request);</br>
    }</br>
}</br>

从这里可以看到，initContextHolder()方法中完成了RequestContextHolder的requestAttributes设置，
而doService()在这之后调用，DispatcherServlet中的processRequest()方法即在doService()之中，
所以从RequestContextHolder中获取到的就是原来的RequestFacade对象，而不是经过spring mvc处理之后的MultipartHttpServletRequest对象，
其后果就是，从RequestContextHolder获取request后，无法直接通过getParameter()获取参数值。

最便捷的解决办法： 
直接将HttpServletRequest作为spring mvc的方法入参，即可以正确获取参数值。

Jshop简介：http://git.oschina.net/dinguangx/jshop

http://dinguangx.iteye.com/blog/2227049