怎么解决跨域问题

Question

var http_request = false; // 处理返回信息的函数function processRequest() {   if (http_request.readyState != 4) { // 判断对象状态      document.title="正在加载数据……";   }   else {            if (http_request.status == 200) { // 信息已经成功返回，开始处理信息            document.title="数据加载完毕!";            var strHTML = http_request.responseText;            alert("AABBCC:"+strHTML);                /*            var rslt=http_request.responseXML.getElementsByTagName('d1');         for(var i=0;i<rslt.length;i++){            alert(rslt[i].getElementsByTagName('d2')[0].firstChild.data);            alert(rslt[i].getElementsByTagName('d2')[1].firstChild.data);                                            } */            } else { //页面不正常                ;//alert("您所请求的页面有异常。");            }         }     } function send_request() {//初始化、指定处理函数、发送请求的函数 alert(123);     var date = new Date();     http_request = false;  //开始初始化XMLHttpRequest对象  if(window.XMLHttpRequest) { //Mozilla 浏览器   http_request = new XMLHttpRequest();   if (http_request.overrideMimeType) {//设置MiME类别    http_request.overrideMimeType('text/xml');   }  }  else if (window.ActiveXObject) { // IE浏览器   try {    http_request = new ActiveXObject("Msxml2.XMLHTTP");   } catch (e) {    try {     http_request = new ActiveXObject("Microsoft.XMLHTTP");    } catch (e) {}   }  }  if (!http_request) { // 异常，创建对象实例失败   window.alert("不能创建XMLHttpRequest对象实例.");   return false;  }  http_request.onreadystatechange = processRequest;  http_request.open("POST","http://124.127.126.77/VRViewer1.1.0alpha/APP/report_query.php", true);  http_request.setRequestHeader("Content-Type","application/x-www-form-urlencoded;charset=utf-8");    http_request.send("&username="+document.getElementById("username").value+"&report_cxm="+document.getElementById("report_cxm").value+"&report_mm"+document.getElementById("report_mm"));                   }