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JSP&Servlet学习笔记----第4章

HTTP是基于请求/响应的无状态的通信协议。

使服务器记得此次请求与之后请求关系的方式，叫做会话管理。

隐藏域：由浏览器在每次请求时主动告知服务器多次请求间必要的信息。仅适用于一些简单的状态管理，如在线问卷。

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * Created by N3verL4nd on 2017/2/21.
 */
@WebServlet("/questionnaire")
public class HiddenFieldServlet extends HttpServlet {
    private void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
        request.setCharacterEncoding("UTF-8");
        response.setContentType("text/html; charset=UTF-8");
        //response.setHeader("Content-Type", "text/html; charset=UTF-8");
        //response.addHeader("Content-Type", "text/html; charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println(
                "<!DOCTYPE html>"
                + "<html>"
                +"<head>"
                +"<title>问卷调查</title>"
                +"</head>"
                +"<body>"
        );
        String page = request.getParameter("page");
        out.println("<form action='questionnaire' method='post'>");
        if (page == null){
            out.println("问题一：<input type='text' name='p1q1' /><br />");
            out.println("问题二：<input type='text' name='p1q2' /><br />");
            out.println("<input type='submit' name='page' value='下一页' />");
        }else if ("下一页".equals(page)){
            String p1q1 = request.getParameter("p1q1");
            String p1q2 = request.getParameter("p1q2");
            out.println("问题三：<input type='text' name='p2q1' />");
            out.println("<input type='hidden' name='p1q1' value='" + p1q1 + "' />");
            out.println("<input type='hidden' name='p1q2' value='" + p1q2 + "' />");
            out.println("<input type='submit' name='page' value='完成' />");
        }else if ("完成".equals(page)){
            out.println(request.getParameter("p1q1") + "<br />");
            out.println(request.getParameter("p1q2") + "<br />");
            out.println(request.getParameter("p2q1") + "<br />");
        }
        out.println("</form>");
        out.println("</body>");
        out.println("</html>");
        out.close();
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        processRequest(request, response);
    }

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

cookie：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * Created by N3verL4nd on 2017/2/23.
 */
@WebServlet(name = "SetServlet", urlPatterns = {"/setcookies.do"})
public class SetServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        for (int i = 0; i < 5; i++){
            Cookie cookie = new Cookie(String.valueOf(i), "xiya");
            response.addCookie(cookie);
        }

        response.setContentType("text/html; charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println("设置cookies" + "<br />");
        out.println("<a href='showcookies.do'>showcookies</a>");
        out.close();
    }
}

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * Created by N3verL4nd on 2017/2/23.
 */
@WebServlet(name = "ShowServlet", urlPatterns = {"/showcookies.do"})
public class ShowServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html; charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println("<!DOCTYPE html>");
        out.println("<html>");
        out.println("<head>");
        out.println("<title>显示Cookies</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<body>");
        out.println("<table>");
        out.println("<tr>");
        out.println("<th>Cookie Name</th>");
        out.println("<th>Cookie Value</th>");
        out.println("</tr>");
        Cookie[] cookies = request.getCookies();
        if(cookies != null){
            for (Cookie cookie : cookies){
                String key = cookie.getName();
                String value = cookie.getValue();
                out.println("<tr>");
                out.println("<td>" + key + "</td>");
                out.println("<td>" + value + "</td>");
                out.println("</tr>");
            }
        }

        out.println("</table>");
        out.println("</body>");
        out.println("</html>");
    }
}

url重写：其实就是GET请求参数的应用，当服务器响应浏览器上一次请求时，将某些相关信息以超链接方式响应给浏览器，超链接中包含参数信息。

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * Created by N3verL4nd on 2017/2/22.
 */
@WebServlet(name = "SearchServlet", urlPatterns = {"/search.do"})
public class SearchServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html; charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println("<!DOCTYPE html>");
        out.println("<html>");
        out.println("<head>");
        out.println("<title>调查</title>");
        out.println("</head>");
        out.println("<body>");
        String start = request.getParameter("start");
        if (start == null){
            start = "1";
        }
        int count = Integer.parseInt(start);
        int begin = 10 * count - 9;
        int end = 10 * count;

        out.println("第 " + begin + " 到 " + end + " 搜索结果<br />");
        out.println("<ul>");
        for (int i = begin; i <= end; i++){
            out.println("<li>搜索结果" + i + "</li>");
        }
        out.println("</ul>");
        for (int i = 1; i < 10; i++){
            if (i == count){
                out.println(i);
                continue;
            }
            out.println("<a href='search.do?start=" + i + "'>" + i + "</a>");
        }
        out.println("</body>");
        out.println("</html>");
    }
}

在Servlet/JSP中可以使用HttpSession来进行会话管理。

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * Created by N3verL4nd on 2017/2/22.
 */
@WebServlet(name = "SessionServlet", urlPatterns = {"/session.do"})
public class SessionServlet extends HttpServlet {

    private void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
        request.setCharacterEncoding("UTF-8");
        response.setContentType("text/html; charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println(
                "<!DOCTYPE html>"
                        + "<html>"
                        +"<head>"
                        +"<title>问卷调查</title>"
                        +"</head>"
                        +"<body>"
        );
        String page = request.getParameter("page");
        out.println("<form action='session.do' method='post'>");
        if (page == null){
            out.println("问题一：<input type='text' name='p1q1' /><br />");
            out.println("问题二：<input type='text' name='p1q2' /><br />");
            out.println("<input type='submit' name='page' value='下一页' />");
        }else if ("下一页".equals(page)){
            String p1q1 = request.getParameter("p1q1");
            String p1q2 = request.getParameter("p1q2");
            HttpSession session = request.getSession();
            System.out.println(session.getId());
            session.setAttribute("p1q1", p1q1);
            session.setAttribute("p1q2", p1q2);
            out.println("问题三：<input type='text' name='p2q1' /><br />");
            out.println("<input type='submit' name='page' value='完成' />");
        }else if ("完成".equals(page)){
            String p2q1 = request.getParameter("p2q1");
            HttpSession session = request.getSession();
            System.out.println(session.getId());
            session.setAttribute("p2q1", p2q1);

            out.println(session.getAttribute("p1q1") + "<br />");
            out.println(session.getAttribute("p1q2") + "<br />");
            out.println(session.getAttribute("p2q1") + "<br />");
        }
        out.println("</form>");
        out.println("</body>");
        out.println("</html>");
        out.close();
    }

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

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

如上所示，HttpSession是通过HttpServletRequest获得的，但是该实例存在于Web容器内。

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

/**
 * Created by N3verL4nd on 2017/2/23.
 */
@WebServlet(name = "SessionInfoServlet", urlPatterns = {"/SessionInfoServlet"})
public class SessionInfoServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html; charset=UTF-8");
        HttpSession session = request.getSession();
        //session.setMaxInactiveInterval(10);//多少秒失效
        PrintWriter out = response.getWriter();
        out.println("<!DOCTYPE html>");
        out.println("<html>");
        out.println("<head>");
        out.println("<title>SessionInfoServlet</title>");
        out.println("</head>");
        out.println("<body>");

        out.println("New Session:" + session.isNew() + "<br />");
        out.println("Session ID:" + session.getId() + "<br />");
        out.println("getCreationTime:" + new Date(session.getCreationTime()) + "<br />");
        out.println("getLastAccessedTime:" + new Date(session.getLastAccessedTime()) + "<br />");
        out.println("getRequestedSessionId:" + request.getRequestedSessionId() + "<br />");
        out.println("isRequestedSessionIdFromURL:" + request.isRequestedSessionIdFromURL() + "<br />");
        out.println("isRequestedSessionIdFromCookie:" + request.isRequestedSessionIdFromCookie() + "<br />");
        out.println("isRequestedSessionIdValid:" + request.isRequestedSessionIdValid() + "<br />");
        out.println("<br /><a href='" + response.encodeURL("SessionInfoServlet") + "'>刷新</a><br />");
    }
}

对于以上程序，我们使用Fiddler抓包观察下：

第一次调用该Servlet会返回Set-Cookie，第二次调用我们会向HTTP服务器发送该cookie来获取Web容器内对应的HttpSession。

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原文地址：https://www.cnblogs.com/lgh1992314/p/6616233.html