模拟jQuery ajax服务器端与客户端通信
本案例通过jQuery和Servlet技术来判断用户名是否存在，让读者明白jQuery是怎么调用服务器后台的。还给出了解决中文乱码的方案和如何避免各种浏览器的缓存。
功能如下：
如果用户名为空提示“用户名不能为空 ”
如果用户名存在提示“用户名[xxxxxx]已经存在，请使用其他用户名, 4 ”
如果用户名不存在提示“用户名[xxxxxx]尚未存在，可以使用该用户名注册, 5”
运行效果如下：
目录结构：
服务器端AjaxServer
package
com.ljq.test;
import
java.io.IOException;
import
java.io.PrintWriter;
import
java.net.URLDecoder;
import
javax.servlet.ServletException;
import
javax.servlet.http.HttpServlet;
import
javax.servlet.http.HttpServletRequest;
import
javax.servlet.http.HttpServletResponse;
@SuppressWarnings(
"
serial
"
)
public
class
AjaxServer
extends
HttpServlet {
@Override
protected
void
doGet(HttpServletRequest request,
HttpServletResponse response)
throws
ServletException, IOException {
try
{
//
设置页面utf-8编码
response.setContentType(
"
text/html;charset=utf-8
"
);
PrintWriter out
=
response.getWriter();
Integer total
=
(Integer) request.getSession().getAttribute(
"
total
"
);
int
temp
=
0
;
if
(total
==
null
) {
temp
=
1
;
}
else
{
temp
=
total.intValue()
+
1
;
}
request.getSession().setAttribute(
"
total
"
, temp);
//
1.取参数
String param
=
request.getParameter(
"
name
"
);
String name
=
URLDecoder.decode(param,
"
UTF-8
"
);
//
2、检查参数是否有效
if
(param
==
null
||
param.length()
==
0
) {
out.println(
"
用户名不能为空
"
);
}
else
{
//
3、校验操作
if
(name.equals(
"
linjiqin
"
)) {
//
4、返回结果数据
out.println(
"
用户名[
"
+
name
+
"
]已经存在，请使用其他用户名,
"
+
temp);
}
else
{
out.println(
"
用户名[
"
+
name
+
"
]尚未存在，可以使用该用户名注册,
"
+
temp);
}
}
}
catch
(Exception e) {
e.printStackTrace();
}
}
@Override
protected
void
doPost(HttpServletRequest request,
HttpServletResponse response)
throws
ServletException, IOException {
doGet(request, response);
}
}
配置web.xml
<?
xml version
=
"
1.0
"
encoding
=
"
UTF-8
"
?>
<
web
-
app version
=
"
2.4
"
xmlns
=
"
http://java.sun.com/xml/ns/j2ee
"
xmlns:xsi
=
"
http://www.w3.org/2001/XMLSchema-instance
"
xsi:schemaLocation
=
"
http://java.sun.com/xml/ns/j2ee
http:
//
java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<
servlet
>
<
servlet
-
name
>
AjaxServer
</
servlet
-
name
>
<
servlet
-
class
>
com.ljq.test.AjaxServer
</
servlet
-
class
>
</
servlet
>
<
servlet
-
mapping
>
<
servlet
-
name
>
AjaxServer
</
servlet
-
name
>
<
url
-
pattern
>/
servlet
/
ajaxServer
</
url
-
pattern
>
</
servlet
-
mapping
>
<
welcome
-
file
-
list
>
<
welcome
-
file
>
index.jsp
</
welcome
-
file
>
</
welcome
-
file
-
list
>
</
web
-
app
>
index.jsp页面
<%
@ page language
=
"
java
"
import
=
"
java.util.*
"
pageEncoding
=
"
UTF-8
"
%>
<%
String path
=
request.getContextPath();
String basePath
=
request.getScheme()
+
"
://
"
+
request.getServerName()
+
"
:
"
+
request.getServerPort()
+
path
+
"
/
"
;
%>
<!
DOCTYPE HTML PUBLIC
"
-//W3C//DTD HTML 4.01 Transitional//EN
"
>
<
html
>
<
head
>
<
base href
=
"
<%=basePath%>
"
>
<
title
>
My JSP
'
index.jsp
'
starting page
</
title
>
<
meta http
-
equiv
=
"
pragma
"
content
=
"
no-cache
"
>
<
meta http
-
equiv
=
"
cache-control
"
content
=
"
no-cache
"
>
<
meta http
-
equiv
=
"
expires
"
content
=
"
0
"
>
<
meta http
-
equiv
=
"
keywords
"
content
=
"
keyword1,keyword2,keyword3
"
>
<
meta http
-
equiv
=
"
description
"
content
=
"
This is my page
"
>
<
script type
=
"
text/javascript
"
src
=
"
<%=request.getContextPath() %>/js/jquery-1.3.1.js
"
></
script
>
<
script type
=
"
text/javascript
"
src
=
"
<%=request.getContextPath() %>/js/validate.js
"
></
script
>
</
head
>
<
body
>
<!--
html5的标准: 首先标签名要小写，其次标签必须关闭，第三属性名遵循骆驼命名法，第四属性值必须位于双引号中
-->
请输入用户名：
<
br
/>
<
input id
=
"
userName
"
/>
<
input type
=
"
button
"
value
=
"
校 验
"
onclick
=
"
verify();
"
/>
<
div id
=
"
result
"
></
div
>
</
body
>
</
html
>
validate.js
function verify() {
//
解决中文乱码方法一： 页面端发出的数据作一次encodeURI，服务器段使用new String(name.getBytes("iso8859-1"),"UTF-8");
//
解决中文乱码方法二： 页面端发出的数据作两次encodeURI，服务器段使用URLDecoder.decode(name,"UTF-8")
var url
=
"
servlet/ajaxServer?name=
"
+
encodeURI(encodeURI($(
"
#userName
"
).val()));
//
注意url前不要加"/"，否则无法访问url
//
var url = "/servlet/ajaxServer?name=" + encodeURI(encodeURI($("#userName").val()));
//
错误
url
=
convertURL(url);
$.get(url,
null
, function(data) {
$(
"
#result
"
).html(data);
});
}
//
给url地址增加时间戳，骗过浏览器，不读取缓存
function convertURL(url) {
//
获取时间戳
var timstamp
=
(
new
Date()).valueOf();
//
将时间戳信息拼接到url上
if
(url.indexOf(
"
?
"
)
>=
0
) {
url
=
url
+
"
&t=
"
+
timstamp;
}
else
{
url
=
url
+
"
?t=
"
+
timstamp;
}
return
url;
}