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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