纯手写AJAX

function createXmlHttpRequest(){

        if(window.ActiveXObject){

          return new ActiveXObject("Microsoft.XMLHTTP");

        }else if(window.XMLHttpRequest){

          return new XMLHttpRequest();

        }

      }

  function getCompanyName(object){

      var carNumber = object.value ;         

      alert(carNumber);

      /**发动请求到服务器*/

      //请求字符串

      var url = "/xdoa/ajaxbookinginfoservlet?carNumber ="+carNumber;

      //创建XMLHttpRequest组件

      xmlHttpRequest = createXmlHttpRequest();

      // 设置回调函数

      xmlHttpRequest.onreadystatechange = callback ;

      // 初始化 XmlHttpRequest 组件

      xmlHttpRequest.open("GET",url,true);

      //发送请求

      xmlHttpRequest.send(null);

  }

  function callback(){

       if( xmlHttpRequest.readyState == 4 && xmlHttpRequest.status == 200 ){

        var b = xmlHttpRequest.responseXML.getElementsByTagName("result").firstChild.data;

        document.getElementById("companyName").value = b ;

     }

  }

response.setContentType(CONTENT_TYPE);

    PrintWriter out = response.getWriter();

    String carNumber = new String(request.getParameter("carNumber").getBytes("ISO-8859-1"),"GBK");

    BookingInformationBean object = new BookingInformationBean();

    BookingInformationService objectService = new BookingInformationService();

    String companyName = objectService.getCompanyByCarNumber(carNumber);

    response.setCharacterEncoding("UTF-8");

    response.setContentType("text/xml;");

    response.setHeader("Cache-Control", "no-cache");

    out.println("<response>");

    out.println("<result>" + companyName + "</result>");

    out.println("</response>");

    out.close();