Ajax基础教程（4）- 实现基本Ajax技术 4.7 动态更新Web页面
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内容摘要：如前所述，如果页面中只有一小部分需要修改，此时Ajax技术最适用。换句话说，以前实现一些用例时，为了更新页面中的一小部分总是需要使用完全页面刷新，这些用例就很适合采用Ajax技术。
点击Add按钮启动数据库插入操作。基于Add按钮的onclick事件将调用addEmployee函数。addEmployee函数使用createAddQueryString来建立查询串，其中包括用户输入的员工姓名、职位和部门信息。创建XMLHttpRequest对象并设置onreadystatechange事件处理程序后，请求提交到服务器。
代码清单4-14列出了处理请求的Java servlet，当接收到请求时将调用servlet的doGet方法。这个方法获取查询串action参数的值，并把请求指向适当的方法。如果是增加信息，请求指向addEmployee方法。
代码清单4-14 EmployeeListServlet.java
package ajaxbook.chap4;
import java.io.*;
import java.net.*;
import java.util.Random;
import javax.servlet.*;
import javax.servlet.http.*;
public class EmployeeListServlet extends HttpServlet {
protected void addEmployee(HttpServletRequest request
, HttpServletResponse response)
throws ServletException, IOException {
//Store the object in the database
String uniqueID = storeEmployee();
//Create the response XML
StringBuffer xml = new StringBuffer("<result><uniqueID>");
xml.append(uniqueID);
xml.append("</uniqueID>");
xml.append("</result>");
//Send the response back to the browser
sendResponse(response, xml.toString());
}
protected void deleteEmployee(HttpServletRequest request
, HttpServletResponse response)
throws ServletException, IOException {
String id = request.getParameter("id");
/* Assume that a call is made to delete the employee from the database */
//Create the response XML
StringBuffer xml = new StringBuffer("<result>");
xml.append("<status>1</status>");
xml.append("</result>");
//Send the response back to the browser
sendResponse(response, xml.toString());
}
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String action = request.getParameter("action");
if(action.equals("add")) {
addEmployee(request, response);
}
else if(action.equals("delete")) {
deleteEmployee(request, response);
}
}
private String storeEmployee() {
/* Assume that the employee is saved to a database and the
* database creates a unique ID. Return the unique ID to the
* calling method. In this case, make up a unique ID.
*/
String uniqueID = "";
Random randomizer = new Random(System.currentTimeMillis());
for(int i = 0; i < 8; i++) {
uniqueID += randomizer.nextInt(9);
}
return uniqueID;
}
private void sendResponse(HttpServletResponse response, String responseText)
throws IOException {
response.setContentType("text/xml");
response.getWriter().write(responseText);
}
}
来源：CSDN 责编：豆豆技术应用
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