当浏览器向服务器发送请求时，web容器会把浏览器的请求信息封装到一个HttpServletRequest对象中去，用户可以通过这个对象获取请求的头信息，请求提交的参数，请求的路径，获取客户端的信息和请求的转发等。
一、获取客户端信息
（1）getRequestURL()：返回客户端发出请求时完整的URL地址。
（2）getRequestURI()：返回请求行中的资源名部分。
（3）getQueryString()：返回请求行中的参数部分。
（4）getPathInfo()：返回请求URL中的额外路径信息。额外路径信息是请求URL中的位于Servlet的路径之后和查询参数之前的内容，它以“/”开头。
（5）getRemoteAddr()：返回客户端的ip地址。
（6）getRemoteHost()：返回客户端的完整的主机名。
（7）getLocalAddr()：获取web服务器的ip地址。
（8）getLocalName()：获取web服务器的主机名。
public class TestRequestServlet extends HttpServlet{ private static final long serialVersionUID = 1L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doPost(req,resp); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setCharacterEncoding("utf-8"); response.setHeader("content-type","text/html;charset=UTF-8"); PrintWriter writer = response.getWriter(); String requestURL = request.getRequestURL().toString(); String requestURI = request.getRequestURI(); String queryString = request.getQueryString(); String pathInfo = request.getPathInfo(); String remoteAddr = request.getRemoteAddr(); int remotePort = request.getRemotePort(); String remoteHost = request.getRemoteHost(); String localAddr = request.getLocalAddr(); String localName = request.getLocalName(); int localPort = request.getLocalPort(); writer.println("requestURL:"+requestURL); writer.println("<br/>"); writer.println("requestURI:"+requestURI); writer.println("<br/>"); writer.println("queryString:"+queryString); writer.println("<br/>"); writer.println("pathInfo:"+pathInfo); writer.println("<br/>"); writer.println("remoteAddr:"+remoteAddr); writer.println("<br/>"); writer.println("remoteHost:"+remoteHost); writer.println("<br/>"); writer.println("localAddr:"+localAddr); writer.println("<br/>"); writer.println("localName:"+localName); writer.println("<br/>"); writer.println("remotePort:"+remotePort); writer.println("<br/>"); writer.println("localPort:"+localPort); writer.flush(); writer.close(); } }
在浏览器上输入地址：http://test.manager.com:8080/web/request?id=12
二、获取客户机的请求头信息
（1）getHeader(string name)：获取请求头中name对应的值
（2）getHeaderNames()：获取请求中的所有的name，返回一个Enumeration<String>
（3）getHeaders(String name)：获取请求头中name对应的所有值，返回一个Enumeration<String>
public class TestRequestHeader extends HttpServlet{ private static final long serialVersionUID = 1L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doPost(req,resp); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setCharacterEncoding("utf-8"); response.setHeader("content-type","text/html;charset=UTF-8"); PrintWriter writer = response.getWriter(); Enumeration<String> enums = request.getHeaderNames(); writer.println("获取请求头信息如下：<br/>"); while(enums.hasMoreElements()){ String name = enums.nextElement(); String value = request.getHeader(name); writer.println(name+":"+value+"<br/>"); } writer.flush(); writer.close(); } }
在浏览器中输入：http://test.manager.com:8080/web/requestheader
三、获取客户机请求参数
（1）getParameter(String name)：根据name获取请求参数的值。
（2）getParameterValues(String name)：根据name获取请求的参数列表。
（3）getParameterMap()：返回的是一个Map类型的值，该返回值记录着前端（如jsp页面）所提交请求中的请求参数和请求参数值的映射关系。(编写框架时常用)
<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%> <!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; utf-8"> <title>Insert title here</title> </head> <body> <form action="<%=request.getContextPath()%>/getParameterRequest" method="post"> <div> <span>名字:</span> <input type="text" name="name" placeholder="请输入名字"> </div> <div> <span>密码:</span> <input type="password" name="password" placeholder="请输入密码"> </div> <div> <span>性别:</span> <input type="radio" name="sex" value="男" checked>男 <input type="radio" name="sex" value="女">女 </div> <div> <span>爱好:</span> <input type="checkbox" name="hobby" value="唱歌">唱歌 <input type="checkbox" name="hobby" value="上网">上网 <input type="checkbox" name="hobby" value="打游戏">打游戏 <input type="checkbox" name="hobby" value="游泳">游泳 <input type="checkbox" name="hobby" value="睡觉">睡觉 </div> <div> <span>所在城市:</span> <select name="city"> <option value="北京">北京</option> <option value="上海">上海</option> <option value="广州">广州</option> <option value="深圳">深圳</option> </select> </div> <dir> <input type="submit" value="提交" /> </dir> </form> </body> </html>
编写一个servlet通过HttpServletRequest对象获取参数：
public class TestRequestParam extends HttpServlet{ private static final long serialVersionUID = 1L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doPost(req,resp); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setCharacterEncoding("utf-8"); response.setHeader("content-type","text/html;charset=UTF-8"); request.setCharacterEncoding("utf-8"); //解决post方式提交request接收中文乱码问题 String name = request.getParameter("name"); String password = request.getParameter("password"); String sex = request.getParameter("sex"); String city = request.getParameter("city"); String[] hobbys= request.getParameterValues("hobby"); String hobbyStr = String.join(",", hobbys); PrintWriter writer = response.getWriter(); writer.print("name参数为:"+name+"<br/>"); writer.print("password参数为:"+password+"<br/>"); writer.print("sex参数为:"+sex+"<br/>"); writer.print("city参数为:"+city+"<br/>"); writer.print("hobbyStr参数为:"+hobbyStr+"<br/>"); writer.flush(); writer.close(); } }
浏览器输出：
三、请求的转发
请求转发指一个web资源收到客户端请求后，通知服务器去调用另外一个web资源进行处理。在Servlet中我们可以使用两种方式实现请求的转发：1、使用ServletContext对象的getRequestDispatcher(path)或者使用HttpServletRequest对象的getRequestDispatcher(path)方法获取RequestDispatcher对象，然后调用RequestDispatcher对象的forward(request,response)方法。
<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%> <!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; utf-8"> <title>Insert title here</title> </head> <body> <form action="<%=request.getContextPath()%>/testReqestForwar1" method="post"> <div> <span>用户名:</span> <input type="text" name="name" placeholder="请输入名字"> </div> <div> <input type="submit" value="提交" /> </div> </form> </body> </html>
TestReqestForward1:
public class TestReqestForward1 extends HttpServlet{ private static final long serialVersionUID = 1L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doPost(req,resp); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.getRequestDispatcher("/testReqestForwar2").forward(request, response); } }
TestReqestForward2:
public class TestReqestForward2 extends HttpServlet{ private static final long serialVersionUID = 1L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doPost(req,resp); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setCharacterEncoding("utf-8"); response.setHeader("content-type","text/html;charset=UTF-8"); request.setCharacterEncoding("utf-8"); //解决post方式提交request接收中文乱码问题 String name = request.getParameter("name"); PrintWriter writer = response.getWriter(); writer.print("name参数为:"+name+"<br/>"); } }
请求到了TestReqestForward1中的doPost方法后被重定向到了TestReqestForward2。
这里我找到了一幅时序图可以很清楚的展示出请求是如何转发到TestReqestForward2。
转载图片地址：https://img-blog.csdn.net/20160427164748927?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast。