ajax

ajax（Asynchronous JavaScript and XML, 非同步 JavaScript 及 XML技术）;两大功能:
   在不重新读取页面的情況下对服务器送出请求，如连动下拉列表呀；
   解析、使用 XML 文件.

function getActDefined(stateVal); {
		var url = "/servlet/InitAddCustSelect?servCode=" + stateVal;//stateVal是从页面上传到后台servlet的值。
        if (window.XMLHttpRequest); {//// Mozilla, Safari.....
			req = new XMLHttpRequest();;
        } else if (window.ActiveXObject); {//IE(可跨浏览器);
			req = new ActiveXObject("Microsoft.XMLHTTP");;
        }
        if(req); {
	req.open("GET", url, true);;
	req.onreadystatechange = complete;//指定的函式名称后不加括号
	req.send(null);;
        }
}

complete函数，接受返回值并解析。

function complete(); {
         if (req.readyState == 4); {//request的返回状态；4表示数据已传回
	if (req.status == 200); {//http接受数据状态；200ok,404文件未找到；500服务器内部错
	var values = req.responseXML.getElementsByTagName("actDefinedId");;//解析
	var lables = req.responseXML.getElementsByTagName("name");;			document.theForm.Act_define_id.length = values.length;
	for(var i = 0; i < values.length; i++); {			        document.theForm.Act_define_id.options[i].value = values[i].firstChild.data;//读入下拉表。		document.theForm.Act_define_id.options[i].text = lables[i].firstChild.data;
	}}
}
}

处理业务的servlet:

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.sql.*;
import topway.common.Helper;
import topway.business.SelectParam;
public class InitAddCustSelect
    extends HttpServlet {
  public InitAddCustSelect(); {
    super();;
  }
  public void destroy(); {
    super.destroy();;
  }
  public void doGet(HttpServletRequest request, HttpServletResponse response); throws
      ServletException, IOException {
      response.setContentType("text/xml;CHARSET=utf8");;
    response.setHeader("Cache-Control", "no-cache");;
    String state = request.getParameter("servCode");;//接收request传来的参数
       StringBuffer sb = new StringBuffer(
        "<?xml version=\"1.0\" encoding=\"GB2312\"?>");;
    sb.append("<addCustSelect>");;
    Connection conn = null;
    try {
      conn = Helper.getConnection();;
      SelectParam selectBean = new SelectParam();;
      ResultSet actDefine = selectBean.getActDefine(conn, state);;
      while (actDefine.next();); {
        sb.append("<actDefinedId>" + actDefine.getString(1); + "</actDefinedId>");;
        sb.append("<name>" + actDefine.getString(2); + "</name>");;
        sb.append("<prepayFee>" + actDefine.getString(3); + "</prepayFee>");;
        sb.append("<firstInstallFee>" + actDefine.getString(4); +
                  "</firstInstallFee>");;
        sb.append("<ipnums>" + actDefine.getString(5); + "</ipnums>");;
      }
    }
    catch (SQLException ex); {
      ex.printStackTrace();;
    }
    finally {
      try {
        conn.close();;
      }
      catch (SQLException ex); {
        ex.printStackTrace();;
      }
    }
    sb.append("</addCustSelect>");;
    PrintWriter out = response.getWriter();;
    out.write(sb.toString(););;//输出
    out.close();;
  }

  public void doPost(HttpServletRequest request, HttpServletResponse response); throws
      ServletException, IOException {
    doGet(request, response);;
  }
}

加载webapplication时初始化servlet,在web.xml中：

<servlet>
                <servlet-name>ServletNames</servlet-name>
	<servlet-class>cn.common.InitAddCustSelect</servlet-class>
</servlet>
<servlet-mapping>
	<servlet-name>ServletNames</servlet-name>
	<url-pattern>/servlet/InitAddCustSelect</url-pattern>
</servlet-mapping>