request 获取请求头

/********************************************************servlet页面****************************************************************/

package request;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.util.Enumeration;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.beanutils.BeanUtils;

import bean.User;

import com.sun.org.apache.regexp.internal.REUtil;
//获取请求头
//获取请求数据的时候一般都要先检查，再使用
public class RequestDemo2 extends HttpServlet {

   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       //获取客户端超链接或表单提交过来的数据
       //1，直接获取
       String value = request.getParameter("username");
       //先判断value的值是否符合要求，再使用
       if(value!=null && !value.trim().equals(""))
           System.out.println(value);

       System.out.println("--------------");
       //通过提交数据的名称获得值
       //2，先得到所有名称，再根据名称获得值
       Enumeration e = request.getParameterNames();
       while (e.hasMoreElements()) {
           String name = (String) e.nextElement();
           value = request.getParameter(name);
           System.out.println(name +" = "+value);
       }

       System.out.println("--------------");

       //3,获取指定名称的所有值
       String[] values = request.getParameterValues("username");
       //这样写程序健壮性不够，如果客户机表单没有填写数据就提交，此时values就为空
       //执行下面的语句就会报空指针异常
//       for(String v:values){
//           System.out.println(v);
//       }
       //这样写，才不会报措
       for(int i=0;values!=null && i<values.length;i++){
           System.out.println(values[i]);
       }

       //4
       Map map = request.getParameterMap();
       User user = new User();
       try {
           BeanUtils.populate(user, map);
       } catch (Exception e1) {
           e1.printStackTrace();
       }
       System.out.println(user);
   }

   //获取头相关的数据
   private void test1(HttpServletRequest request) {
       //获取头信息
       //1
       String headValue = request.getHeader("Accept-Encoding");
       System.out.println(headValue);

       System.out.println("-----------------------");
       //2
       Enumeration e = request.getHeaders("Accept-Encoding");
       while(e.hasMoreElements()){
           String value = (String) e.nextElement();
           System.out.println(value);
       }
       System.out.println("-----------------");
       //3
       e = request.getHeaderNames();
       while (e.hasMoreElements()) {
           String name = (String) e.nextElement();
           String value = request.getHeader("name");
           System.out.println(value);

       }
   }


   protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       doGet(request, response);
   }

}
/********************************************************html页面**********************************************************************************/

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>提交数据</title>
</head>
<body>
   
   <a href="/requestandresponse/RequestDemo2?username=xxxxxx">点点</a>
   
   <form action="/requestandresponse/RequestDemo2" method="post">
       用户名：<input type="text" name="username"/>
       <input type="submit" value="提交">
   </form>
</body>
</html>