原来HTTP协议这么简单！一文读懂HttpServletRequest
一、HttpServletRequest介绍
HttpServletRequest对象代表客户端的请求，当客户端通过HTTP协议访问服务器时，HTTP请求头中的所有信息都封装在这个对象中，通过这个对象提供的方法，可以获得客户端请求的所有信息。
二、jsp页面引入js，css文件的方式
在eclipse中新建一个web项目，目录结构如下：
在jsp页面的最开始，获取项目的根路径：
<% String path = request.getContextPath(); String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/"; %>
在中，插入下述代码：
<base href="<%=basePath%>" />
这句代码的作用是将整个页面的根路径设置为项目路径。
三、Request常用方法
1、获得客户机信息
getRequestURL()返回客户端发出请求时的完整URL。getRequestURI()返回请求行中的资源名部分。getQueryString ()返回请求行中的参数部分。getRemoteAddr()返回发出请求的客户机的IP地址。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。getRemoteHost()返回发出请求的客户机的完整主机名。getRemotePort()返回客户机所使用的网络端口号。getLocalAddr()返回WEB服务器的IP地址。getLocalName()返回WEB服务器的主机名。
private void RequestMessages(HttpServletRequest req, HttpServletResponse resp) throws IOException{
String reqUrl = req.getRequestURL().toString();//得到请求的URL地址
String reqUri = req.getRequestURI();//得到请求的资源
String queryString = req.getQueryString();//得到请求的URL地址中附带的参数
String remoteAddr = req.getRemoteAddr();//得到来访者的IP地址
String remoteHost = req.getRemoteHost();
int remotePort = req.getRemotePort();
String remoteUser = req.getRemoteUser();
String method = req.getMethod();//得到请求URL地址时使用的方法
String pathInfo = req.getPathInfo();
String localAddr = req.getLocalAddr();//获取WEB服务器的IP地址
String localName = req.getLocalName();//获取WEB服务器的主机名
resp.setCharacterEncoding("UTF-8");//设置将字符以"UTF-8"编码输出到客户端浏览器
//通过设置响应头控制浏览器以UTF-8的编码显示数据，如果不加这句话，那么浏览器显示的将是乱码
resp.setHeader("content-type", "text/html;charset=UTF-8");
PrintWriter out = resp.getWriter();
out.write("获取到的客户机信息如下：");
out.write("<br/>");
out.write("请求的URL地址："+reqUrl);
out.write("<br/>");
out.write("请求的资源："+reqUri);
out.write("<br/>");
out.write("请求的URL地址中附带的参数："+queryString);
out.write("<br/>");
out.write("来访者的IP地址："+remoteAddr);
out.write("<br/>");
out.write("来访者的主机名："+remoteHost);
out.write("<br/>");
out.write("使用的端口号："+remotePort);
out.write("<br/>");
out.write("remoteUser："+remoteUser);
out.write("<br/>");
out.write("请求使用的方法："+method);
out.write("<br/>");
out.write("pathInfo："+pathInfo);
out.write("<br/>");
out.write("localAddr："+localAddr);
out.write("<br/>");
out.write("localName："+localName);
} 
2、获得客户机请求头
- getHeader(string name)方法:String
- getHeaders(String name)方法:Enumeration
- getHeaderNames()方法
private void RequestHead(HttpServletRequest req, HttpServletResponse resp) throws IOException{
resp.setCharacterEncoding("UTF-8");//设置将字符以"UTF-8"编码输出到客户端浏览器
//通过设置响应头控制浏览器以UTF-8的编码显示数据
resp.setHeader("content-type", "text/html;charset=UTF-8");
PrintWriter out = resp.getWriter();
Enumeration<String> reqHeadInfos = req.getHeaderNames();//获取所有的请求头
out.write("获取到的客户端所有的请求头信息如下：");
out.write("<br/>");
while (reqHeadInfos.hasMoreElements()) {
String headName = (String) reqHeadInfos.nextElement();
String headValue = req.getHeader(headName);//根据请求头的名字获取对应的请求头的值
out.write(headName+":"+headValue);
out.write("<br/>");
}
out.write("<br/>");
out.write("获取到的客户端Accept-Encoding请求头的值：");
out.write("<br/>");
String value = req.getHeader("Accept-Encoding");//获取Accept-Encoding请求头对应的值
out.write(value);
Enumeration<String> e = req.getHeaders("Accept-Encoding");
while (e.hasMoreElements()) {
String string = (String) e.nextElement();
System.out.println(string);
}
} 
3、获得客户机请求参数
getParameter(String name)根据name获取请求参数(常用)getParameterValues(String name)根据name获取请求参数列表(常用)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"%> <% String path = request.getContextPath(); String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/"; %> <html> <head> <base href="<%=basePath%>" /> <meta http-equiv="Content-Type" content="text/html;charset=UTF-8"> <title>表单提交</title> <link href="css/bootstrap.css" rel="stylesheet"> <script src="js/jquery-3.2.1.js"></script> <script src="js/bootstrap.js"></script> </head> <body> <form class="form-horizontal" action="<%=request.getContextPath()%>/GetParameterRequest.html" role="form" method="post"> <div class="form-group"> <label for="firstname" class="col-sm-1 control-label">名字</label> <div class="col-sm-3"> <input type="text" class="form-control" name="name" placeholder="请输入名字"> </div> </div> <div class="form-group"> <label for="lastname" class="col-sm-1 control-label">年龄</label> <div class="col-sm-3"> <input type="text" class="form-control" name="age" placeholder="请输年龄"> </div> </div> <div class="form-group"> <label for="lastname" class="col-sm-1 control-label">性别</label> <div class="col-sm-3"> <input type="radio" name="sex" value="男" checked>男 <input type="radio" name="sex" value="女">女 </div> </div> <div class="form-group"> <label for="lastname" class="col-sm-1 control-label">爱好</label> <div class="col-sm-3"> <input type="checkbox" name="aihao" value="唱歌">唱歌 <input type="checkbox" name="aihao" value="上网">上网 <input type="checkbox" name="aihao" value="游戏">游戏 <input type="checkbox" name="aihao" value="看书">看书 </div> </div> <div class="form-group"> <div class="col-sm-offset-1 col-sm-3"> <button type="submit" class="btn btn-default">提交</button> <button type="reset" class="btn btn-default">重置</button> </div> </div> </form> </body> </html>
使用getParameter方法和getParameterValues方法接收表单参数：
public class GetParameterRequest extends HttpServlet{
private static final long serialVersionUID = 3903946972744326948L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//客户端是以UTF-8编码提交表单数据的，所以需要设置服务器端以UTF-8的编码进行接收，否则对于中文数据就会产生乱码
req.setCharacterEncoding("UTF-8");
//获取名字
String name = req.getParameter("name");
//获取年龄
String age = req.getParameter("age");
//获取性别
String sex = req.getParameter("sex");
//获取爱好，因为可以选中多个值，所以获取到的值是一个字符串数组，因此需要使用getParameterValues方法来获取
String[] aihaos = req.getParameterValues("aihao");
String aihao = "";
if(aihaos != null){
for (int i = 0; i < aihaos.length; i++) {
if(i == aihaos.length - 1){
aihao += aihaos[i];
} else {
aihao += aihaos[i] + ",";
}
}
}
System.out.println("名字：" + name);
System.out.println("年龄：" + age);
System.out.println("性别：" + sex);
System.out.println("爱好：" + aihao);
req.setAttribute("aihao", aihao);
//设置服务器端以UTF-8编码输出数据到客户端
resp.setCharacterEncoding("UTF-8");
this.getServletContext().getRequestDispatcher("/request.jsp").forward(req, resp);
}
} 响应页面：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme() + "://"
+ request.getServerName() + ":" + request.getServerPort()
+ path + "/";
%>
<html>
<head>
<base href="<%=basePath%>" />
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<title>表单提交</title>
<link href="css/bootstrap.css" rel="stylesheet">
<script src="js/jquery-3.2.1.js"></script>
<script src="js/bootstrap.js"></script>
</head>
<body>
<table class="table">
<thead>
<tr>
<th>名称</th>
<th>结果</th>
</tr>
</thead>
<tbody>
<tr>
<td>姓名</td>
<td><%=request.getParameter("name") %></td>
</tr>
<tr>
<td>年龄</td>
<td><%=request.getParameter("age") %></td>
</tr>
<tr>
<td>性别</td>
<td><%=request.getParameter("sex") %></td>
</tr>
<tr>
<td>爱好</td>
<td><%=request.getAttribute("aihao") %></td>
</tr>
</tbody>
</table>
</body>
</html> 提交如下表单：
后台打印：
运行结果如下：
四、request接收表单提交中文参数乱码问题
1、以POST方式提交表单中文参数的乱码问题
有如下表单：
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/"; %> <html> <head> <base href="<%=basePath%>" /> <meta http-equiv="Content-Type" content="text/html;charset=UTF-8"> <title>表单提交</title> <link href="css/bootstrap.css" rel="stylesheet"> <script src="js/jquery-3.2.1.js"></script> <script src="js/bootstrap.js"></script> </head> <body> <form class="form-horizontal" action="<%=request.getContextPath()%>/PostRequest.html" role="form" method="post"> <div class="form-group"> <label for="firstname" class="col-sm-1 control-label">名字</label> <div class="col-sm-3"> <input type="text" class="form-control" name="name" placeholder="请输入名字"> </div> </div> <div class="form-group"> <div class="col-sm-offset-1 col-sm-3"> <button type="submit" class="btn btn-default">提交</button> <button type="reset" class="btn btn-default">重置</button> </div> </div> </form> </body> </html>
后台接收参数：
public class PostRequest extends HttpServlet{
private static final long serialVersionUID = 3903946972744326948L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String name = req.getParameter("name");
System.out.println("名字：" + name);
}
} 提交数据：
运行结果：
之所以会产生乱码，就是因为服务器和客户端沟通的编码不一致造成的，因此解决的办法是：在客户端和服务器之间设置一个统一的编码，之后就按照此编码进行数据的传输和接收。
由于客户端是以UTF-8字符编码将表单数据传输到服务器端的，因此服务器也需要设置以UTF-8字符编码进行接收，通过setCharacterEncoding方法统一编码格式：
public class PostRequest extends HttpServlet{
private static final long serialVersionUID = 3903946972744326948L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//设置服务器以UTF-8的编码接收数据
req.setCharacterEncoding("UTF-8");
String name = req.getParameter("name");
System.out.println("名字：" + name);
}
} 重新提交表单，中文乱码解决：
2、以GET方式提交表单中文参数的乱码问题
有如下表单：
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/"; %> <html> <head> <base href="<%=basePath%>" /> <meta http-equiv="Content-Type" content="text/html;charset=UTF-8"> <title>表单提交</title> <link href="css/bootstrap.css" rel="stylesheet"> <script src="js/jquery-3.2.1.js"></script> <script src="js/bootstrap.js"></script> </head> <body> <form class="form-horizontal" action="<%=request.getContextPath()%>/GetRequest.html" role="form" method="get"> <div class="form-group"> <label for="firstname" class="col-sm-1 control-label">名字</label> <div class="col-sm-3"> <input type="text" class="form-control" name="name" placeholder="请输入名字"> </div> </div> <div class="form-group"> <div class="col-sm-offset-1 col-sm-3"> <button type="submit" class="btn btn-default">提交</button> <button type="reset" class="btn btn-default">重置</button> </div> </div> </form> </body> </html>
后台接收参数：
public class GetRequest extends HttpServlet{
private static final long serialVersionUID = 3903946972744326948L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String name = req.getParameter("name");
System.out.println("名字：" + name);
}
} 提交数据：
运行结果：
之所以会产生乱码，对于以get方式传输的数据，默认的还是使用ISO8859-1这个字符编码来接收数据，客户端以UTF-8的编码传输数据到服务器端，而服务器端的request对象使用的是ISO8859-1这个字符编码来接收数据，服务器和客户端沟通的编码不一致因此才会产生中文乱码的。
解决方法：
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