Request原理

1、request对象和responset对象是由服务器创建的，我们来使用他们。

2、request对象用来获取请求消息，response对象用来设置响应消息。

Request功能

获取请求消息数据

• 获取请求行数据
  请求行格式：
  GET /learning/demo1?name=zhangsan HTTP/1.1
  方法：

   			1、获取请求方式 String getMethod()2、(**)获取虚拟目录String getContextPath()3、获取Servlet路径（资源路径）String getServletPath()4、获取get方式请求参数String getQueryString()5、(***)获取请求uri及urlString getRequestURI()  /learning/demo1StringBuffer getRequestURI() http:localhost/learning/demo1URI：统一资源定位符，范围大，例如共和国URL：统一资源标识符，范围小，例如 中华人民共和国6、获取协议及版本 HTTP/1.1String getProtocol()7、获取客户机的IP地址String getRemoteAddr()
  

@WebServlet( "/requestDemo1")
public class RequestDemo1 extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//1 获取请求方式 GETString method = request.getMethod();System.out.println(method);//2获取虚拟目录String contextPath = request.getContextPath();System.out.println(contextPath);//3 获取资源目录/requestDemo1String servletPath = request.getServletPath();System.out.println(servletPath);//4 获取get请求参数name=lisiString queryString = request.getQueryString();System.out.println(queryString);//5 获取uri/requestDemo1String requestURI = request.getRequestURI();StringBuffer requestURL = request.getRequestURL();System.out.println(requestURI);System.out.println(requestURL);//http://localhost:8080/requestDemo1//6 获取主机 0:0:0:0:0:0:0:1String remoteAddr = request.getRemoteAddr();System.out.println(remoteAddr);//7 获取协议 HTTP/1.1String protocol = request.getProtocol();System.out.println(protocol);}
}

• 获取请求头
  方法：
  （1）获取请求头的所有name：
  Enumeration getHeaderNames();
  （2）获取请求头的值
  String getHeader(name);

@WebServlet("/request/RequestDemo2")
public class RequestDemo2 extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//获取请求头Enumeration<String> headerNames = request.getHeaderNames();//遍历while(headerNames.hasMoreElements()){//System.out.println(headerNames.nextElement());String name = headerNames.nextElement();//(***)获取请求头的值String header = request.getHeader(name);System.out.println(name+":"+header);}}
}

（3）根据请求头user-agent的值解决不同浏览器的兼容

@WebServlet("/request/RequestDemo3")
public class RequestDemo3 extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String header = request.getHeader("user-agent");if(header.contains("Firefox"))System.out.println("火狐来了");else if(header.contains("IE"))System.out.println("ie 来了");}
}

• 获取请求体
  通过post方式的才有请求体
  步骤：1、获取流对象
  字节输入流getInputStream()
  字符输入流getReader()
  2、再从流对象中拿数据

@WebServlet( "/RequestDemo5")
public class RequestDemo5 extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//获取请求消息体-消息参数BufferedReader br = request.getReader();//读取数据，从br里把数据读取出来String line = null;while((line=br.readLine())!=null){System.out.println(line);//username=lll&password=123}}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}
}

Request其他功能

1、获取请求参数通用方式：不论get还是post都可以
（1）String getParamter(String name)
（2）String[] getParamterValues(String name)
（3）getParamterNames()
（4）Map<String,String[]> getParamterMap
（5） tip:获取参数前，设置编码
request.setCharacterEncoding(“utf-8”);
2、请求转发：一种在服务器内部的url跳转方式
(1)步骤
①通过request对象获取请求转发器对象：
②使用 进行转发：forward （*****）
request.getRequestDispatcher(转发资源路径).forward(request,response);
(2)特点
①浏览器地址栏路径不发生变化
②只能转发到当前服务器内部资源中
③转发是一次请求
3、共享数据
*域对象：一个有作用范围的对象，在范围内共享数据
request域：代表一次请求的范围，用于请求转发的多个资源中共享数据
*方法：
（1）setAttribute():存储数据
（2）getAttribute()：获取
（3）removeAttribute()：移除
4、获取ServletContext
ServletContext servletContext = request.getServletContext();

//获取请求参数通用方式
@WebServlet( "/RequestDemo6")
public class RequestDemo6 extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.setCharacterEncoding("utf-8");String username = request.getParameter("username");
//        System.out.println("post");
//        System.out.println(username);String[] hobbies = request.getParameterValues("hobby");
//        for (String hobby : hobbies) {
//            System.out.println(hobby);
//        }Enumeration<String> parameterNames = request.getParameterNames();
//        while(parameterNames.hasMoreElements()){
//            String name = parameterNames.nextElement();
//            System.out.println(name);
//            String parameter = request.getParameter(name);
//            System.out.println(name+":"+parameter);
//        }Map<String, String[]> parameterMap = request.getParameterMap();//遍历entrySet和keySet两种方法Set<String> keySet = parameterMap.keySet();Iterator<String> iterator = keySet.iterator();while(iterator.hasNext()){String it = iterator.next();System.out.println(it);String[] values = parameterMap.get(it);for (String value : values) {System.out.println(value);}System.out.println("------");}}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doPost(request,response);}
}

//请求转发和共享数据
@WebServlet( "/RequestDemo7")
public class RequestDemo7 extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request,response);}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("demo7 comes");//存储数据到request域中request.setAttribute("msg","hello");//转发到demo8资源request.getRequestDispatcher("/RequestDemo8").forward(request,response);}
}