ajax实例--注册

package cn.ajax;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;public class RegisterServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {request.setCharacterEncoding("utf-8");response.setCharacterEncoding("utf-8");response.setContentType("text/html");PrintWriter out = response.getWriter();System.out.println("register   dopost");String username = request.getParameter("username");if ("sa".equals(username)) {out.println("用户名已经存在");}else {out.println("用户名可以使用");}}}