Ajax——异步检查用户名是否存在示例

在任何网站注册用户的时候，都会检查用户是否已经存在。很久以前的处理方式是将所有数据提交到服务器端进行验证，很显然这种方式的用户体验很不好；后来有了Ajax，有了异步交互，当用户输完用户名继续填写其他信息的时候，Ajax就将信息发到了服务器去检查该用户名是否已经被注册了，这样如果用户名已经存在，不用等用户将所有数据都提交就可以给出提示。采用这种方式大大改善了用户体验。
regist.jsp
复制代码 代码如下:
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>

用户名:

密码:

CheckServlet.java
复制代码 代码如下:
public class CheckServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public static final String DBDRIVER = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
public static final String DBURL = "jdbc:sqlserver://localhost:1433;DatabaseName=bbs";
public static final String DBUSER = "sa";
public static final String DBPASS = "pass";

public CheckServlet() {
super();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("UTF-8");
response.setContentType("text/html");
Connection conn = null;
PreparedStatement pst = null;
ResultSet rs = null;
PrintWriter out = response.getWriter();
String username = request.getParameter("usernaem");
try{
Class.forName(DBDRIVER);
conn = DriverManager.getConnection(DBURL,DBUSER,DBPASS);
String sql = "select count(username) from user where username=?";
pst = conn.prepareStatement(sql);
pst.setString(1,username);
rs = pst.executeQuery();
if(rs.next()){
if(rs.getInt(1)>0){//用户名已经存在了
out.print("true");
}else{
out.print("false");
}

}
}catch(Exception e){
e.printStackTrace();
}finally{
try{
conn.close();
}catch(Exception e){
e.printStackTrace();
}
}
}
}