dwr方法调用session过期问题的解决方法

项目使用Ext作为表现层，由dwr异步调用义务逻辑方法，通过filter过滤请求来实现权限管理，通过检查session中是否有User对象来判断是否为登陆用户。 这样做出现一个问题，当session过期时，异步调用方法无法得到相应的提示。

于是要通过对dwr.engine 进行修改来实现session 过期时有适当的提示信息。要点如下：

1. 在web.xml配置filter，对dwr方法调用路径进行拦截，url-partern(*.dwr);

    在filter中编写代码，当session中有User对象时放行，session没有User对象时，执行response.setStatus(1000); 1000使我们自己指定的状态码。

2. 在jsp页面中引入dwr的js文件后执行如下js代码：

  

 

      dwr.engine._stateChange = function(batch) {
      var toEval;
     
      if (batch.completed) {
        dwr.engine._debug("Error: _stateChange() with batch.completed");
        return;
      }
    
      var req = batch.req;
      try {
        if (req.readyState != 4) return;
      }
      catch (ex) {
        dwr.engine._handleWarning(batch, ex);
        // It's broken - clear up and forget this call
        dwr.engine._clearUp(batch);
        return;
      }
    
      try {
        var reply = req.responseText;
        reply = dwr.engine._replyRewriteHandler(reply);
        var status = req.status; // causes Mozilla to except on page moves
    
        if (reply == null || reply == "") {
          dwr.engine._handleWarning(batch, { name:"dwr.engine.missingData", message:"No data       received from server" });
        }
        else if (status != 200) {
          if ( status == 1000) {
           alert("未登录或登录超时，请重新登录");
           return;
          }
          dwr.engine._handleError(batch, { name:"dwr.engine.http." + status,     message:req.statusText });
        }
        else {
          var contentType = req.getResponseHeader("Content-Type");
          if (!contentType.match(/^text\/plain/) && !contentType.match(/^text\/javascript/)) {
            if (contentType.match(/^text\/html/) && typeof batch.textHtmlHandler == "function") {
              batch.textHtmlHandler();
            }
            else {
              dwr.engine._handleWarning(batch, { name:"dwr.engine.invalidMimeType", message:"Invalid content type: '" + contentType + "'" });
            }
          }
          else {
            // Comet replies might have already partially executed
            if (batch.isPoll && batch.map.partialResponse == dwr.engine._partialResponseYes) {
              dwr.engine._processCometResponse(reply, batch);
            }
            else {
              if (reply.search("//#DWR") == -1) {
                dwr.engine._handleWarning(batch, { name:"dwr.engine.invalidReply", message:"Invalid reply from server" });
              }
              else {
                toEval = reply;
              }
            }
          }
        }
      }
      catch (ex) {
        dwr.engine._handleWarning(batch, ex);
      }
    
      dwr.engine._callPostHooks(batch);
    
      // Outside of the try/catch so errors propogate normally:
      dwr.engine._receivedBatch = batch;
      if (toEval != null) toEval = toEval.replace(dwr.engine._scriptTagProtection, "");
      dwr.engine._eval(toEval);
      dwr.engine._receivedBatch = null;
    
      dwr.engine._clearUp(batch);
    };
      

其中红色的代码是我们添加的，其余为engine.js的源代码，我们状态为我们制定的1000时，弹出提示信息，并且中止执行其他其他操作，不再执行回调函数。