4.检索客户端有关信息： String getMethod()：返回请求使用的HTTP方法名，如GET、POST或PUT等； String getRemoteHost() ：返回客户端的主机名； String getRemoteAddr() ：返回客户端的IP地址； int getRemotePort()：返回客户端IP地址的端口号； String getProtocol()：返回客户使用的请求协议名和版本； String getRequestURI()：返回请求行中URL的查询串的前面部分； String getQueryString()：返回请求行中URL的查询串的内容；
package com.demo; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Servlet implementation class ClientInfoServlet */ @WebServlet("/client-information") public class ClientInfoServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); PrintWriter out=response.getWriter(); out.print("<html><head><title>客户端信息</title></head><body>"); out.print("<p>客户端信息：</p>"); out.print(request.getMethod()+""+request.getRequestURI()+""+request.getProtocol()+"<br>"); out.print("<p>客户主机名："+request.getRemoteHost()+"</p>"); out.print("<p>客户IP地址："+request.getRemoteAddr()+"</p>"); out.print("<p>端口号："+request.getRemotePort()+"</p>"); out.print("</body></html>"); } }5.检索请求头信息 HTTP请求头是随请求一起发送到服务器的信息，它是以"名/值"对的形式发送。例如，关于浏览器的信息就是通过User-Agent请求头发送的。
package com.demo; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Servlet implementation class ClientInfoServlet */ @WebServlet("/client-information") public class ClientInfoServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); PrintWriter out=response.getWriter(); out.print("<html><head><title>客户端信息</title></head><body>"); out.print("<p>客户端信息：</p>"); out.print(request.getMethod()+""+request.getRequestURI()+""+request.getProtocol()+"<br>"); out.print("<p>客户主机名："+request.getRemoteHost()+"</p>"); out.print("<p>客户IP地址："+request.getRemoteAddr()+"</p>"); out.print("<p>端口号："+request.getRemotePort()+"</p>"); out.print("</body></html>"); } }