AJAX
AJAX：即“Asynchronous Javascript And XML”（异步的JavaScript和XML），是指一种创建交互式网页应用的网页开发技术，尤其是在一种在无需重新加载整个网页的情况下，能够更新部分网页的技术。
传统Web开发
World Wide Web（简称Web）：是随着Internet的普及使用而发展起来的一门技术，其开发模式是一种请求→刷新→响应的模式，每个请求由单独的一个页面来显示，发送一个请求就会重新获取这个页面。
Ajax采用异步通信，主要以数据交互为主；传统的web开发采用同步通信，主要以页面交互为主。
例子：在页面写一个生成随机数的表单
用form表单提交的方式
index.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
$Title$
random.do
@WebServlet(name = "randomServlet",urlPatterns = "/random.do")
public class randomServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String strmax = request.getParameter("max");
int max = Integer.parseInt(strmax);
Random random = new Random();
int num = random.nextInt(max);
request.setAttribute("num",num);
request.setAttribute("max",max);
request.getRequestDispatcher("index.jsp").forward(request,response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
}
用这种方式是向后台提交整个网页
下面用ajax方式
ajax请求步骤
1.创建Ajax对象
var request = new XMLHttpRequest();
2.连接服务器
open(method,url,async);
request.open("get","query.do",true);
//get或者post（多用get），请求的服务器地址，同步（false）或者异步（true）请求
3.发送请求
send(string)
在使用GET方式请求时无需填写参数,对数据库无害的时候用get
req.open('get','random.do?max=100‘,true);
req.send();
在使用POST方式时参数代表着向服务器发送的数据
req.open('post','random.do',true);
req.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
//post请求需要设置HTTP头信息,否则发送数据有问题
req.send('max=100');
4.接收服务器相应数据
req.onload = function () {
console.log(req.responseText);
}
index.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
$Title$
random.do
@WebServlet(name = "randomServlet",urlPatterns = "/random.do")
public class randomServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String strmax = request.getParameter("max");
int max = Integer.parseInt(strmax);
Random random = new Random();
int num = random.nextInt(max);
PrintWriter printWriter = response.getWriter();
printWriter.println(num);
// request.setAttribute("num",num);
// request.setAttribute("max",max);
// request.getRequestDispatcher("index.jsp").forward(request,response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request,response);
}
}
ajax校验用户名是否已存在
index.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
$Title$
reg.do
@WebServlet(name = "regServlet",urlPatterns = "/reg.do")
public class regServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String username = request.getParameter("username");
if(username.equals("admin")){
response.getWriter().println(1);
}
else {
response.getWriter().println(0);
}
}
}