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tomcat集群时统计session与在线人数

news 来源：原创 2024/5/3 21:52:22

　　tomcat集群时，原来通过HttpSessionListener实现类监听session的创建和销毁来统计在线人数的方法不再有效，因为不是每个人登陆都会在同一个tomcat服务器上，而在另一台tomcat上登陆的人的session是通过session复制创建的，而复制过程不会调用HttpSessionListener接口的方法，也一直没找着如何监听session复制的方法，所以就没法统计在线人了。

今天突然回想起tomcat下的manager应用上面就能看到session数和session的内容，于是本文的实现原理就是，做一个类似这样的servlet，此servlet把tomcat上负责管理应用的对象保存下来，供我任意使用。在tomcat上看应用的信息时，使用的是http://localhost:8080/manager/html/list这个路径，页面信息见下图：

　　于是把源码下来看看 (apache-tomcat-6.0.39-src)，细看tomcat下webapps/manager/WEB-INF/web.xml文件配置，发现原来tomcat是通过org.apache.catalina.manager.ManagerServlet这个类来提供以上服务的，跟踪此类doGet方法代码

 1 // --------------------------------------------------------- Public Methods
 2 
 3     /**
 4      * Process a GET request for the specified resource.
 5      * 
 6      * @param request
 7      *            The servlet request we are processing
 8      * @param response
 9      *            The servlet response we are creating
10      * 
11      * @exception IOException
12      *                if an input/output error occurs
13      * @exception ServletException
14      *                if a servlet-specified error occurs
15      */
16     public void doGet(HttpServletRequest request, HttpServletResponse response)
17             throws IOException, ServletException {
18 
19         // Identify the request parameters that we need
20         // 取得访问路径，
21         String command = request.getPathInfo();
22 
23         String path = request.getParameter("path");
24         String deployPath = request.getParameter("deployPath");
25         String deployConfig = request.getParameter("deployConfig");
26         String deployWar = request.getParameter("deployWar");
27 
28         // Prepare our output writer to generate the response message
29         response.setContentType("text/html; charset=" + Constants.CHARSET);
30 
31         String message = "";
32         // Process the requested command
33         if (command == null || command.equals("/")) {
34         } else if (command.equals("/deploy")) {
35             message = deployInternal(deployConfig, deployPath, deployWar);
36             // 找到了，就是这个路径，往下看list方法
37         } else if (command.equals("/list")) {
38         } else if (command.equals("/reload")) {
39             message = reload(path);
40         } else if (command.equals("/undeploy")) {
41             message = undeploy(path);
42         } else if (command.equals("/expire")) {
43             message = expireSessions(path, request);
44         } else if (command.equals("/sessions")) {
45             try {
46                 doSessions(path, request, response);
47                 return;
48             } catch (Exception e) {
49                 log("HTMLManagerServlet.sessions[" + path + "]", e);
50                 message = sm
51                         .getString("managerServlet.exception", e.toString());
52             }
53         } else if (command.equals("/start")) {
54             message = start(path);
55         } else if (command.equals("/stop")) {
56             message = stop(path);
57         } else if (command.equals("/findleaks")) {
58             message = findleaks();
59         } else {
60             message = sm.getString("managerServlet.unknownCommand", command);
61         }
62         // 就是这个方法生成上面的那个页面
63         list(request, response, message);
64     }

list

  1 /**
  2      * Render a HTML list of the currently active Contexts in our virtual host,
  3      * and memory and server status information.
  4      * 
  5      * @param request
  6      *            The request
  7      * @param response
  8      *            The response
  9      * @param message
 10      *            a message to display
 11      */
 12     public void list(HttpServletRequest request, HttpServletResponse response,
 13             String message) throws IOException {
 14 
 15         if (debug >= 1)
 16             log("list: Listing contexts for virtual host '" + host.getName()
 17                     + "'");
 18 
 19         PrintWriter writer = response.getWriter();
 20 
 21         // HTML Header Section
 22         writer.print(Constants.HTML_HEADER_SECTION);
 23 
 24         // Body Header Section
 25         Object[] args = new Object[2];
 26         args[0] = request.getContextPath();
 27         args[1] = sm.getString("htmlManagerServlet.title");
 28         writer.print(MessageFormat.format(Constants.BODY_HEADER_SECTION, args));
 29 
 30         // Message Section
 31         args = new Object[3];
 32         args[0] = sm.getString("htmlManagerServlet.messageLabel");
 33         if (message == null || message.length() == 0) {
 34             args[1] = "OK";
 35         } else {
 36             args[1] = RequestUtil.filter(message);
 37         }
 38         writer.print(MessageFormat.format(Constants.MESSAGE_SECTION, args));
 39 
 40         // Manager Section
 41         args = new Object[9];
 42         args[0] = sm.getString("htmlManagerServlet.manager");
 43         args[1] = response.encodeURL(request.getContextPath() + "/html/list");
 44         args[2] = sm.getString("htmlManagerServlet.list");
 45         args[3] = response.encodeURL(request.getContextPath() + "/"
 46                 + sm.getString("htmlManagerServlet.helpHtmlManagerFile"));
 47         args[4] = sm.getString("htmlManagerServlet.helpHtmlManager");
 48         args[5] = response.encodeURL(request.getContextPath() + "/"
 49                 + sm.getString("htmlManagerServlet.helpManagerFile"));
 50         args[6] = sm.getString("htmlManagerServlet.helpManager");
 51         args[7] = response.encodeURL(request.getContextPath() + "/status");
 52         args[8] = sm.getString("statusServlet.title");
 53         writer.print(MessageFormat.format(Constants.MANAGER_SECTION, args));
 54 
 55         // Apps Header Section
 56         args = new Object[6];
 57         args[0] = sm.getString("htmlManagerServlet.appsTitle");
 58         args[1] = sm.getString("htmlManagerServlet.appsPath");
 59         args[2] = sm.getString("htmlManagerServlet.appsName");
 60         args[3] = sm.getString("htmlManagerServlet.appsAvailable");
 61         args[4] = sm.getString("htmlManagerServlet.appsSessions");
 62         args[5] = sm.getString("htmlManagerServlet.appsTasks");
 63         writer.print(MessageFormat.format(APPS_HEADER_SECTION, args));
 64 
 65         // Apps Row Section
 66         // Create sorted map of deployed applications context paths.
 67 
 68         // host就当是当前的tomcat吧，那么contexts就此tomcat下的所有应用
 69         Container children[] = host.findChildren();
 70         String contextPaths[] = new String[children.length];
 71         // 循环每个应用
 72         for (int i = 0; i < children.length; i++)
 73             // 应用名称
 74             contextPaths[i] = children[i].getName();
 75 
 76         TreeMap sortedContextPathsMap = new TreeMap();
 77 
 78         for (int i = 0; i < contextPaths.length; i++) {
 79             // 应用部署路径
 80             String displayPath = contextPaths[i];
 81             sortedContextPathsMap.put(displayPath, contextPaths[i]);
 82         }
 83 
 84         String appsStart = sm.getString("htmlManagerServlet.appsStart");
 85         String appsStop = sm.getString("htmlManagerServlet.appsStop");
 86         String appsReload = sm.getString("htmlManagerServlet.appsReload");
 87         String appsUndeploy = sm.getString("htmlManagerServlet.appsUndeploy");
 88         String appsExpire = sm.getString("htmlManagerServlet.appsExpire");
 89 
 90         Iterator iterator = sortedContextPathsMap.entrySet().iterator();
 91         boolean isHighlighted = true;
 92         boolean isDeployed = true;
 93         String highlightColor = null;
 94 
 95         while (iterator.hasNext()) {
 96             // Bugzilla 34818, alternating row colors
 97             isHighlighted = !isHighlighted;
 98             if (isHighlighted) {
 99                 highlightColor = "#C3F3C3";
100             } else {
101                 highlightColor = "#FFFFFF";
102             }
103 
104             Map.Entry entry = (Map.Entry) iterator.next();
105             String displayPath = (String) entry.getKey();
106             String contextPath = (String) entry.getValue();
107             Context context = (Context) host.findChild(contextPath);
108             if (displayPath.equals("")) {
109                 displayPath = "/";
110             }
111 
112             if (context != null) {
113                 try {
114                     isDeployed = isDeployed(contextPath);
115                 } catch (Exception e) {
116                     // Assume false on failure for safety
117                     isDeployed = false;
118                 }
119 
120                 args = new Object[7];
121                 args[0] = URL_ENCODER.encode(contextPath + "/");
122                 args[1] = RequestUtil.filter(displayPath);
123                 if (context.getDisplayName() == null) {
124                     args[2] = "&nbsp;";
125                 } else {
126                     args[2] = RequestUtil.filter(context.getDisplayName());
127                 }
128                 managerServlet
129                 // 应用是否已启动
130                 args[3] = new Boolean(context.getAvailable());
131                 args[4] = response.encodeURL(request.getContextPath()
132                         + "/html/sessions?path="
133                         + URL_ENCODER.encode(displayPath));
134                 if (context.getManager() != null) {
135                     args[5] = new Integer(context.getManager()
136                             .getActiveSessions());
137                 } else {
138                     args[5] = new Integer(0);
139                 }
140 
141                 args[6] = highlightColor;
142                 //打印出一行关于此应用的信息，应用的URL，当前状态，session数等，具体见上图  
143                 writer.print(MessageFormat.format(APPS_ROW_DETAILS_SECTION,
144                         args));
145 
146                 args = new Object[14];
147                 args[0] = response
148                         .encodeURL(request.getContextPath()
149                                 + "/html/start?path="
150                                 + URL_ENCODER.encode(displayPath));
151                 args[1] = appsStart;
152                 args[2] = response.encodeURL(request.getContextPath()
153                         + "/html/stop?path=" + URL_ENCODER.encode(displayPath));
154                 args[3] = appsStop;
155                 args[4] = response.encodeURL(request.getContextPath()
156                         + "/html/reload?path="
157                         + URL_ENCODER.encode(displayPath));
158                 args[5] = appsReload;
159                 args[6] = response.encodeURL(request.getContextPath()
160                         + "/html/undeploy?path="
161                         + URL_ENCODER.encode(displayPath));
162                 args[7] = appsUndeploy;
163 
164                 args[8] = response.encodeURL(request.getContextPath()
165                         + "/html/expire?path="
166                         + URL_ENCODER.encode(displayPath));
167                 args[9] = appsExpire;
168                 args[10] = sm.getString("htmlManagerServlet.expire.explain");
169                 Manager manager = context.getManager();
170                 if (manager == null) {
171                     args[11] = sm.getString("htmlManagerServlet.noManager");
172                 } else {
173                     args[11] = new Integer(context.getManager()
174                             .getMaxInactiveInterval() / 60);
175                 }
176                 args[12] = sm.getString("htmlManagerServlet.expire.unit");
177 
178                 args[13] = highlightColor;
179 
180                 if (context.getPath().equals(this.context.getPath())) {
181                     writer.print(MessageFormat.format(
182                             MANAGER_APP_ROW_BUTTON_SECTION, args));
183                 } else if (context.getAvailable() && isDeployed) {
184                     writer.print(MessageFormat.format(
185                             STARTED_DEPLOYED_APPS_ROW_BUTTON_SECTION, args));
186                 } else if (context.getAvailable() && !isDeployed) {
187                     writer.print(MessageFormat.format(
188                             STARTED_NONDEPLOYED_APPS_ROW_BUTTON_SECTION, args));
189                 } else if (!context.getAvailable() && isDeployed) {
190                     writer.print(MessageFormat.format(
191                             STOPPED_DEPLOYED_APPS_ROW_BUTTON_SECTION, args));
192                 } else {
193                     writer.print(MessageFormat.format(
194                             STOPPED_NONDEPLOYED_APPS_ROW_BUTTON_SECTION, args));
195                 }
196 
197             }
198         }
199 
200         // Deploy Section
201         args = new Object[7];
202         args[0] = sm.getString("htmlManagerServlet.deployTitle");
203         args[1] = sm.getString("htmlManagerServlet.deployServer");
204         args[2] = response.encodeURL(request.getContextPath() + "/html/deploy");
205         args[3] = sm.getString("htmlManagerServlet.deployPath");
206         args[4] = sm.getString("htmlManagerServlet.deployConfig");
207         args[5] = sm.getString("htmlManagerServlet.deployWar");
208         args[6] = sm.getString("htmlManagerServlet.deployButton");
209         writer.print(MessageFormat.format(DEPLOY_SECTION, args));
210 
211         args = new Object[4];
212         args[0] = sm.getString("htmlManagerServlet.deployUpload");
213         args[1] = response.encodeURL(request.getContextPath() + "/html/upload");
214         args[2] = sm.getString("htmlManagerServlet.deployUploadFile");
215         args[3] = sm.getString("htmlManagerServlet.deployButton");
216         writer.print(MessageFormat.format(UPLOAD_SECTION, args));
217 
218         // Diagnostics section
219         args = new Object[5];
220         args[0] = sm.getString("htmlManagerServlet.diagnosticsTitle");
221         args[1] = sm.getString("htmlManagerServlet.diagnosticsLeak");
222         args[2] = response.encodeURL(request.getContextPath()
223                 + "/html/findleaks");
224         args[3] = sm.getString("htmlManagerServlet.diagnosticsLeakWarning");
225         args[4] = sm.getString("htmlManagerServlet.diagnosticsLeakButton");
226         writer.print(MessageFormat.format(DIAGNOSTICS_SECTION, args));
227 
228         // Server Header Section
229         args = new Object[7];
230         args[0] = sm.getString("htmlManagerServlet.serverTitle");
231         args[1] = sm.getString("htmlManagerServlet.serverVersion");
232         args[2] = sm.getString("htmlManagerServlet.serverJVMVersion");
233         args[3] = sm.getString("htmlManagerServlet.serverJVMVendor");
234         args[4] = sm.getString("htmlManagerServlet.serverOSName");
235         args[5] = sm.getString("htmlManagerServlet.serverOSVersion");
236         args[6] = sm.getString("htmlManagerServlet.serverOSArch");
237         writer.print(MessageFormat
238                 .format(Constants.SERVER_HEADER_SECTION, args));
239 
240         // Server Row Section
241         args = new Object[6];
242         args[0] = ServerInfo.getServerInfo();
243         args[1] = System.getProperty("java.runtime.version");
244         args[2] = System.getProperty("java.vm.vendor");
245         args[3] = System.getProperty("os.name");
246         args[4] = System.getProperty("os.version");
247         args[5] = System.getProperty("os.arch");
248         writer.print(MessageFormat.format(Constants.SERVER_ROW_SECTION, args));
249 
250         // HTML Tail Section
251         writer.print(Constants.HTML_TAIL_SECTION);
252 
253         // Finish up the response
254         writer.flush();
255         writer.close();
256     }

　　注意：context.getManager().findSessions()可以取得所有session，但这是个org.apache.catalina.Session[]数组，不是HttpSession[]数组，但这个Session接口里面有个getSession方法，返回结果正是HttpSession类型，没错，就是循环这个数组并调用其getSession方法就可以取得所有在线用户了

上面的Session[]数组是从context对象里面来的，而context是从host对象来的，host是个初始值为NULL的成员变量，是什么时候赋上值的？是在init方法执行前，setWrapper方法执行时赋的值，请看setWrapper方法代码

public class HostManagerServlet
extends HttpServlet implements ContainerServlet

 1   /**
 2      * Set the Wrapper with which we are associated.
 3      *
 4      * @param wrapper The new wrapper
 5      */
 6     public void setWrapper(Wrapper wrapper) {
 7 
 8         //这里所有需要的对象都有了，其实下面我们需要拿到wrapper就够了
 9         this.wrapper = wrapper;
10         if (wrapper == null) {
11             context = null;
12             host = null;
13             engine = null;
14         } else {
15             context = (Context) wrapper.getParent();
16             host = (Host) context.getParent();
17             engine = (Engine) host.getParent();
18         }
19 
20         // Retrieve the MBean server
21         mBeanServer = Registry.getRegistry(null, null).getMBeanServer();
22         
23     }

　　setWrapper会在初始化时被调用，怎么实现的，首先看web.xml中对此servlet的配置，没什么特别，我们可以发散一下思维，struts2里面action如何能自动注入request对象？Spring如何让service监听事件？答案是一样的，那就是让你的类实现某个接口，你要的东西就给你了，对的，这里也一样，此servlet实现了ContainerServlet接口，初始的时候setWrapper方法才会被调用。

　　是JAVA新手的看这里，我提出上面这些问题，不是想卖什么关子，只是想启发JAVA初学者们，当某天你们做设计时，可以参考这种方法，一句概括就是：只要你实现我的接口，我就可以让你做某事，而不需要任何额外的配置。当然这种设计的缺点就是入侵、偶合。举个简单的应用场景：每天晚上，我用一个定时器通过Spring搜索所有实现了“GarbageCleaner”接口的service bean，并调用其clean方法清理对应模块的垃圾数据，那么任何模块的service只要实现了此接口，就会被调用。

回到正题，我也自已写个servlet并且实ContainerServlet接口吧，使用静态方法取得所有的session，具体代码如下：

 1 package manager.session.http.servlet;
 2 
 3 import java.io.IOException;
 4 import java.util.LinkedHashMap;
 5 import java.util.Map;
 6 
 7 import javax.servlet.ServletException;
 8 import javax.servlet.http.HttpServlet;
 9 import javax.servlet.http.HttpServletRequest;
10 import javax.servlet.http.HttpServletResponse;
11 import javax.servlet.http.HttpSession;
12 
13 import org.apache.catalina.ContainerServlet;
14 import org.apache.catalina.Context;
15 import org.apache.catalina.Session;
16 import org.apache.catalina.Wrapper;
17 
18 public class TomcatWrapperServlet extends HttpServlet implements
19         ContainerServlet {
20     private static final long serialVersionUID = 1L;
21 
22     // 弄个静态变量，初始化后就记下来，以备随时使用
23     private static Wrapper wrapper = null;
24 
25     public Wrapper getWrapper() {
26         return wrapper;
27     }
28 
29     public void setWrapper(Wrapper wrapper) {
30         TomcatWrapperServlet.wrapper = wrapper;
31     }
32 
33     // doGet不做任何事情，只需要接收第一次请求，触发初始动作就完成它的使命了
34     @Override
35     protected void doGet(HttpServletRequest req, HttpServletResponse resp)
36             throws ServletException, IOException {
37         resp.getWriter().println("Hello world!");
38         resp.getWriter().flush();
39         resp.getWriter().close();
40     }
41 
42     // 初始化后可通过此静态方法取得所有session
43     public static Map<String, HttpSession> fillSessions() {
44         if (wrapper == null) {// 没有初始化
45             throw new RuntimeException(
46                     "本servlet未被初始化，您必须先通过URL访问本servlet后，才可以调用这个方法");
47         }
48         Map<String, HttpSession> sessions = new LinkedHashMap<String, HttpSession>();
49 
50         // 取得本应用
51         Context context = (Context) wrapper.getParent();
52         // 取得Session[]数组
53         Session[] temps = context.getManager().findSessions();
54         if (temps != null && temps.length > 0) {
55             for (int j = 0; j < temps.length; j++) {
56                 // Map<sessionId,session>
57                 sessions.put(temps[j].getSession().getId(), temps[j]
58                         .getSession());
59             }
60         }
61         return sessions;
62     }
63 
64 }

　在web.xml配置一下，然后启动应用，访问之，结果出现异常，是一个安全异常：TomcatWrapperServlet is privileged and cannot be loaded by this web application(想想如下)，说我的类是个特权类，不能被普通的web应用加载，为何manager这个应用又可以呢？把manager/META-INF/context.xml复制到我的应用，再加载，再访问，一切搞定，此文件内容只有一句

　　Xml代码

<Context antiResourceLocking="false" privileged="true" />

HTTP Status 500 - Error allocating a servlet instance

type Exception report

message Error allocating a servlet instance

description The server encountered an internal error that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Error allocating a servlet instance
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
	org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:879)
	org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:617)
	org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1760)
	java.lang.Thread.run(Thread.java:722)

root cause

java.lang.SecurityException: Servlet of class manager.session.http.servlet.TomcatWrapperServlet is privileged and cannot be loaded by this web application
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
	org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:879)
	org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:617)
	org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1760)
	java.lang.Thread.run(Thread.java:722)

note The full stack trace of the root cause is available in the Apache Tomcat/6.0.37 logs.