ajax 解决不用跳转即可提示用户名已经被注册……

版权声明：你们随意 我不奉陪了 https://blog.csdn.net/zuoside__lord/article/details/85224870

防止我下次不会写，，所以 先放在这里。

ajax部分

function showHint(str)
{
	//out.println("xxxxxxxx!");
  var xmlhttp;
  if (str.length==0)
  { 
    document.getElementById("txtHint").innerHTML="";
    return;
  }
  if (window.XMLHttpRequest)
  {
    // IE7+, Firefox, Chrome, Opera, Safari 浏览器执行代码
    xmlhttp=new XMLHttpRequest();
  }
  else
  {
    // IE6, IE5 浏览器执行代码
    xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
  xmlhttp.onreadystatechange=function()
  {
    if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
      document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
    }
  }
  xmlhttp.open("post","loginServelt?username="+str,true);
  xmlhttp.send();
}
</script>

jsp部分：格式没有调 就是一个表格

<form action="loginServelt" method="post">
												<div class="row form-group">
													<div class="col-md-12">
														<label for="username">Username or Email</label>
														<input type="text" class="form-control" id="username" onkeyup="showHint(this.value)"/><!-- 此处需要ajax--> 
														<p style="color:red"><span id="txtHint"></span></p> 
														
													</div>
												</div></form>

servelt部分

package servelt;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class loginServelt
 */
//注册

public class loginServelt extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public loginServelt() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=UTF-8");

		String name=request.getParameter("username");
		String password=request.getParameter("password");//
		response.getWriter().write("Username is been taken ");
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);

		
	}

}