Servlet(4)：Session
Session, Cookie及交互
会话（Session）跟踪是Web程序中常用的技术，用来跟踪用户的整个会话。常用的会话跟踪技术是Cookie与Session。
Cookie通过在客户端记录信息确定用户身份，Session通过在服务器端记录信息确定用户身份。
HTTP 是一种"无状态"协议，这意味着每次客户端检索网页时，客户端打开一个单独的连接到 Web 服务器，服务器会自动不保留之前客户端请求的任何记录。
但是仍然有以下三种方式来维持 Web 客户端和 Web 服务器之间的 session 会话：
Cookies：Session创建成功以后，会创建Cookie（key='JSESSIONID', value=Session ID）。通常情况下，一个浏览器的多个Tag可以共享一个Session对象。
隐藏的表单字段（Form适用）：有些浏览器不支持Cookie，可以用表单隐藏域代替。
<input type="hidden" name="sessionid" value="12345">
URL 重写（Link适用）：如果使用URL提交时，可以作为URL参数传递。
http://localhost:8080/ServletTest/login?sessionid=12345
下面是一个使用Cookie来维持Session会话的例子。重点代码讲解在例子中。
package com.servlettest.session; 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;
import javax.servlet.http.HttpSession; /**
* Servlet implementation class Login
*/
@WebServlet("/default")
public class Default extends HttpServlet { private static final long serialVersionUID = 1L; /**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { invalidateSession(request); response.setContentType("text/html");
request.setCharacterEncoding("UTF-8");
response.setCharacterEncoding("UTF-8"); PrintWriter out = response.getWriter();
out.println("<!DOCTYPE html>");
out.println("<html>");
out.println("<head>");
out.println("<title>Login Page</title>");
out.println("</head>");
out.println("<body>");
out.println("<form action=\"login\" method=\"POST\">");
out.println("帐号: <input type=\"text\" name=\"userId\"/><br/>");
out.println("密码: <input type=\"password\" name=\"password\"/><br/>");
out.println("<input type=\"submit\" value=\"提交\"/>"); // HttpServletRequest Attribute和Parameter的区别
// (1) HttpServletRequest 类有setAttribute()方法，而没有setParameter()方法。
// (2) 当两个Web组件之间为链接关系时，被链接的组件通过getParameter()方法来获得请求参数，一般通过表单和链接传递的参数使用getParameter。
// (3) 当两个Web组件之间为转发关系时，转发目标组件通过getAttribute()方法来和转发源组件共享request范围内的数据。
String message = (String) request.getAttribute("message");
if (message != null && message != "") {
out.println("<p>" + message + "</p>");
}
out.println("</body>");
out.println("</html>");
} /**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
} private static void invalidateSession(HttpServletRequest request) {
HttpSession session = request.getSession(false);
if (session != null)
session.invalidate();
}
}
package com.servlettest.session; import java.io.IOException;
import java.util.HashMap;
import java.util.Map; 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; /**
* Servlet implementation class Login
*/
@WebServlet("/login")
public class Login extends HttpServlet { private static final long serialVersionUID = 1L; private static final Map<String, String[]> USER_INFO = initUserInfo(); /**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { response.setContentType("text/html"); request.setCharacterEncoding("UTF-8");
response.setCharacterEncoding("UTF-8"); // 获取用户登录信息
String userId = request.getParameter("userId");
String password = request.getParameter("password");
if ((userId == null || userId == "") || (password == null || password == "")) {
request.getRequestDispatcher("/default").forward(request, response);
} else if (USER_INFO.containsKey(userId)) {
String[] info = USER_INFO.get(userId);
if (info[1].equals(password)) {
// 创建Session
setSession(userId, info[0], request, response);
request.getRequestDispatcher("/welcome1").forward(request, response);
} else {
request.setAttribute("message", "帐号或密码错误!");
request.getRequestDispatcher("/default").forward(request, response);
}
} else {
request.setAttribute("message", "帐号或密码错误!");
request.getRequestDispatcher("/default").forward(request, response);
}
} /**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
} private static Map<String, String[]> initUserInfo() { Map<String, String[]> result = new HashMap<>();
String[] user1 = { "张三", "123" };
result.put("101", user1);
String[] user2 = { "李四", "456" };
result.put("102", user2);
String[] user3 = { "王五", "789" };
result.put("103", user3); return result;
} private void setSession(String userId, String userName, HttpServletRequest request, HttpServletResponse response) {
// 如果不存在 session 会话，则创建一个 session 对象
HttpSession session = request.getSession(true);
String[] userInfo = { userId, userName };
session.setAttribute("USER_INFO", userInfo);
}
}
package com.servlettest.session; import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration; 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; /**
* Servlet implementation class Welcome
*/
@WebServlet("/welcome1")
public class Welcome1 extends HttpServlet { private static final long serialVersionUID = 1L; /**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { response.setContentType("text/html");
request.setCharacterEncoding("UTF-8");
response.setCharacterEncoding("UTF-8"); // 注意request.getSession() 等同于 request.getSession(true)，除非我们确认session一定存在或者sesson不存在时明确有创建session的需要，否则请尽量使用request.getSession(false)
HttpSession session = request.getSession(false);
String[] userInfo = (String[]) session.getAttribute("USER_INFO");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE html>");
out.println("<html>");
out.println("<head>");
out.println("<title>Login Page</title>");
out.println("</head>");
out.println("<body>");
out.println("您好 <b>" + userInfo[0] + "-" + userInfo[1] + "</b>, 这是Welcome1画面!");
out.println("<br/><a href = \"welcome2\">去welcome2</a> | <a href = \"default\">注销</a>");
out.println("<br/>");
out.println("<p>SessionID: " + session.getId() + "</p>");
Enumeration<String> names = session.getAttributeNames();
while (names.hasMoreElements()) {
String name = names.nextElement();
out.println("<p>" + names.nextElement() + ": " + session.getAttribute(name) + "</p>");
}
out.println("</table>");
out.println("</body>");
out.println("</html>");
out.close();
} /**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
package com.servlettest.session; import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration; 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; /**
* Servlet implementation class Welcome
*/
@WebServlet("/welcome2")
public class Welcome2 extends HttpServlet { private static final long serialVersionUID = 1L; /**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { response.setContentType("text/html");
request.setCharacterEncoding("UTF-8");
response.setCharacterEncoding("UTF-8"); // 注意request.getSession() 等同于 request.getSession(true)，除非我们确认session一定存在或者sesson不存在时明确有创建session的需要，否则请尽量使用request.getSession(false)
HttpSession session = request.getSession(false);
String[] userInfo = (String[]) session.getAttribute("USER_INFO");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE html>");
out.println("<html>");
out.println("<head>");
out.println("<title>Login Page</title>");
out.println("</head>");
out.println("<body>");
out.println("您好 <b>" + userInfo[0] + "-" + userInfo[1] + "</b>, 这是Welcome2画面!");
out.println("<br/><a href = \"welcome1\">去welcome1</a> | <a href = \"default\">注销</a>");
out.println("<br/>");
out.println("<p>SessionID: " + session.getId() + "</p>");
Enumeration<String> names = session.getAttributeNames();
while (names.hasMoreElements()) {
String name = names.nextElement();
out.println("<p>" + names.nextElement() + ": " + session.getAttribute(name) + "</p>");
}
out.println("</body>");
out.println("</html>");
out.close();
} /**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
package com.servlettest.filter; import java.io.IOException;
import java.util.ArrayList;
import java.util.List; import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession; import com.servlettest.exception.PermissionException; public class PermissionFilter implements Filter { private final static List<String> URL = new ArrayList<>(); @Override
public void init(FilterConfig arg0) throws ServletException {
URL.add("/ServletTest/welcome1");
URL.add("/ServletTest/welcome2");
} @Override
public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
throws IOException, ServletException {
if (arg0 instanceof HttpServletRequest && arg1 instanceof HttpServletResponse) {
HttpServletRequest req = (HttpServletRequest) arg0;
if (URL.contains(req.getRequestURI())) {
HttpSession session = req.getSession(true);
String[] userInfo = (String[]) session.getAttribute("USER_INFO");
if (userInfo == null) {
throw new PermissionException();
}
}
}
arg2.doFilter(arg0, arg1);
} @Override
public void destroy() {
}
}
package com.servlettest.exception;
public class PermissionException extends RuntimeException {
private static final long serialVersionUID = 1L;
}
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
<title>Forbidden</title>
</head>
<body>
<h2>403 禁止访问所请求的页面</h2>
</body>
</html>
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
id="WebApp_ID" version="3.1">
<filter>
<filter-name>permissionFilter</filter-name>
<filter-class>com.servlettest.filter.PermissionFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>permissionFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<error-page>
<error-code>403</error-code>
<location>/html/forbidden.html</location>
</error-page>
<error-page>
<exception-type>com.servlettest.exception.PermissionException</exception-type>
<location>/html/forbidden.html</location>
</error-page>
<welcome-file-list>
<welcome-file>default</welcome-file>
</welcome-file-list>
<session-config>
<session-timeout>1</session-timeout>
</session-config>
</web-app>
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