{"id":949,"date":"2010-10-02T00:09:54","date_gmt":"2010-10-02T00:09:54","guid":{"rendered":"http:\/\/enjoyasp.net\/?p=949"},"modified":"2010-10-02T00:09:54","modified_gmt":"2010-10-02T00:09:54","slug":"%e7%9b%91%e5%90%ac%e5%99%a8-listener","status":"publish","type":"post","link":"https:\/\/enjoyasp.net\/index.php\/2010\/10\/02\/%e7%9b%91%e5%90%ac%e5%99%a8-listener\/","title":{"rendered":"\u76d1\u542c\u5668 listener"},"content":{"rendered":"<pre lang=\"java\">\r\n\u5e38\u7528\u7684listener\u6709\uff1a\r\n  \uff081\uff09 ServletContextListener \u76d1\u542cServletContext\u3002\r\n        \u5f53\u521b\u5efaServletContext\u65f6\uff0c\u6fc0\u53d1 contextInitialized(ServletContextEvent sce)\u65b9\u6cd5\uff1b\r\n       \u5f53\u9500\u6bc1ServletContext\u65f6\uff0c\u6fc0\u53d1contextDestroyed(ServletContextEvent sce)\u65b9\u6cd5\u3002\r\n\r\n  \uff082\uff09ServletContextAttributeListener\u76d1\u542c\u5bf9ServletContext\u5c5e\u6027\u7684\u64cd\u4f5c\uff0c\u6bd4\u5982\u589e\u52a0\u3001\u5220\u9664\u3001\u4fee\u6539\u5c5e\u6027\u3002\r\n\r\n  \uff083\uff09HttpSessionListener \u76d1\u542cHttpSession\u7684\u64cd\u4f5c\u3002\r\n          \u5f53\u521b\u5efa\u4e00\u4e2aSession\u65f6\uff0c\u6fc0\u53d1 session Created(HttpSessionEvent se)\u65b9\u6cd5\uff1b\r\n          \u5f53\u9500\u6bc1\u4e00\u4e2aSession\u65f6\uff0c\u6fc0\u53d1sessionDestroyed (HttpSessionEvent se)\u65b9\u6cd5\u3002\r\n  \r\n\r\n \uff084\uff09HttpSessionAttributeListener \u76d1\u542cHttpSession\u4e2d\u7684\u5c5e\u6027\u7684\u64cd\u4f5c\u3002\r\n        \u5f53\u5728Session\u589e\u52a0\u4e00\u4e2a\u5c5e\u6027\u65f6\uff0c\u6fc0\u53d1 attributeAdded(HttpSessionBindingEvent se) \u65b9\u6cd5\uff1b\r\n        \u5f53\u5728Session\u5220\u9664\u4e00\u4e2a\u5c5e\u6027\u65f6\uff0c\u6fc0\u53d1attributeRemoved(HttpSessionBindingEventse)\u65b9\u6cd5\uff1b\r\n        \u5f53\u5728Session\u5c5e\u6027\u88ab\u91cd\u65b0\u8bbe\u7f6e\u65f6\uff0c\u6fc0\u53d1attributeReplaced(HttpSessionBindingEvent se) \u65b9\u6cd5\u3002\r\n\r\n1,  SerlvetContextListener \r\n\r\n(1) \u5728\u6bcf\u4e00\u4e2ajava\u7684web\u5e94\u7528\u4e2d\u90fd\u53ea\u80fd\u53c8\u4e00\u4e2a\u5355\u72ec\u7684servlet context\u3002\u800c\u8fd9\u4e2acontext\u88ab\u653e\u7f6e\u5728\u6574\u4e2a\u5e94\u7528\u7ea7\u522b\u4e0a\uff0c\u5f53\u5e94\u7528\u4e00\u65e6\u542f\u52a8\u4e4b\u540e\uff0cservlet\u5bb9\u5668\u5c31\u4f1a\u521b\u5efa\u8fd9\u6837\u4e00\u4e2aservlet context\u6765\u670d\u52a1\u4e8eweb\u5e94\u7528\u3002\u56e0\u6b64\u6211\u4eec\u4e5f\u53ef\u4ee5\u521b\u5efa\u4e00\u4e2a\u7c7b\u5e76\u5b9e\u73b0\u4e86\u4e00\u4e2aServletContextListerner\u63a5\u53e3\uff0c\u7528\u4e8e\u901a\u77e5\u8fd9\u4e2acontext\u662f\u5426\u88ab\u521b\u5efa\u4e86\u6216\u8005\u88ab\u9500\u6bc1\u4e86\u3002\u8fd9\u6837\u5f53Context\u88ab\u521b\u5efa\u65f6\uff0c\u5c31\u4f1a\u6536\u5230\u4e00\u4e2a\u76f8\u5173\u7684\u901a\u77e5\uff0c\u5e76\u4e14\u5728Context\u88ab\u9500\u6bc1\u524d\u4e5f\u4f1a\u5f97\u5230\u4e00\u4e2a\u901a\u77e5\u3002\r\n\u5982\uff1a public void contextInitialized(ServletContextEvent event) {\r\nServletContext ctx = event.getServletContext( );\r\nctx.setAttribute(\"dateStarted\", new Date( ));\r\n\/\/\u5728\u9875\u9762\u6216\u7a0b\u5e8f\u4e2d\u7528&lt;%=getServletContext().getAttribute(\"dateStarted\")%&gt; \u5f97\u5230\u8bbe\u7f6e\u7684\u5c5e\u6027\r\n}\r\n\u6ce8\uff1a\u5728\u4f7f\u7528Struts\u7684\u65f6\u5019\uff0c\u6211\u4eec\u53ef\u4ee5\u91c7\u7528plug-in\u7684\u65b9\u5f0f\u6765\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\u3002\u56e0\u4e3apulg-in\u53ef\u4ee5\u505acontext Listern\u6240\u80fd\u505a\u7684\u4efb\u4f55\u4e8b\u60c5\u3002\u5e76\u4e14\u80fd\u591f\u4f20\u5165\u5404\u79cd\u914d\u7f6e\u5728struts-config.xml\u6587\u4ef6\u4e2d\u7684\u53c2\u6570\u3002\r\n(2)  \u5728web.xml\u4e2d\u914d\u7f6e\r\n\r\n   &lt;listener&gt;\r\n       &lt;listener-class&gt;demo.listener.MyContextLoader&lt;\/listener-class&gt;\r\n  &lt;\/listener&gt;\r\n(2) \u5b9a\u65f6\u4efb\u52a1\u7684\u5b9e\u73b0\r\nimport java.util.Timer;\r\nimport javax.servlet.ServletContextEvent;\r\nimport javax.servlet.ServletContextListener;\r\n\r\npublic class MyListener implements ServletContextListener {\r\n\r\nprivate Timer timer = null;\r\n\r\npublic void contextInitialized(ServletContextEvent event) {\r\ntimer = new Timer(true);\r\n\/\/\u8bbe\u7f6e\u4efb\u52a1\u8ba1\u5212\uff0c\u542f\u52a8\u548c\u95f4\u9694\u65f6\u95f4\r\ntimer.schedule(new MyTask(), 0, 86400000);\r\n}\r\n\r\npublic void contextDestroyed(ServletContextEvent event) {\r\ntimer.cancel();\r\n}\r\n\r\n}\r\n\r\nclass MyTask extends TimerTask {\r\n\r\npublic void run() {\r\n\/\/ System.out.println(\"call at \" + (new Date()));\r\n\/\/ TODO \u6b64\u5904\u6dfb\u52a0\u5177\u4f53\u4efb\u52a1\u4ee3\u7801\r\n}\r\n\r\n2, HttpSessionListener\r\n\r\n\uff081\uff09 \u7528\u6765\u76d1\u542cServlet Context\u7684\u521b\u5efa\u548c\u9500\u6bc1\u7684\u72b6\u6001\r\n\uff082\uff09\u7edf\u8ba1\u5f53\u524d\u6709\u591a\u5c11\u5728\u7ebf\u7528\u6237\uff0c\u539f\u7406\uff1a\u770b\u521b\u5efa\u4e86\u591a\u5c11\u4e2asession\u5373\u53ef\r\n\r\npackage demo.listener;\r\n\r\nimport javax.servlet.ServletContext;\r\nimport javax.servlet.http.HttpSessionEvent;\r\nimport javax.servlet.http.HttpSessionListener;\r\n\r\npublic class SessionCounter implements HttpSessionListener {\r\npublic void sessionCreated(HttpSessionEvent event) {\r\nServletContext ctx = event.getSession( ).getServletContext( );\r\nInteger numSessions = (Integer) ctx.getAttribute(\"numSessions\");\r\n\r\n\/\/\u5728\u9875\u9762\u6216\u7a0b\u5e8f\u4e2d\u7528&lt;%=getServletContext().getAttribute(\"dateStarted\")%&gt; \u5f97\u5230\u4eba\u6570\r\n\r\nif (numSessions == null) {\r\n    numSessions = new Integer(1);\r\n}\r\nelse {\r\n    int count = numSessions.intValue( );\r\n    numSessions = new Integer(count + 1);\r\n}\r\nctx.setAttribute(\"numSessions\", numSessions);\r\n}\r\npublic void sessionDestroyed(HttpSessionEvent event) {\r\nServletContext ctx = event.getSession( ).getServletContext( );\r\nInteger numSessions = (Integer) ctx.getAttribute(\"numSessions\");\r\nif (numSessions == null) {\r\n    numSessions = new Integer(0);\r\n}\r\nelse {\r\n    int count = numSessions.intValue( );\r\n    numSessions = new Integer(count - 1);\r\n}\r\nctx.setAttribute(\"numSessions\", numSessions);\r\n}\r\n}\r\n3, HttpSessionAttributeListener\r\n(1) \u76d1\u542csession\u4e2d\u7684\u5c5e\u6027\u7684\u521b\u5efa\uff0c\u79fb\u9664\u7b49\uff0c\u5982\u5f53\u521b\u5efauserName\u5c5e\u6027\u65f6\u505a\u4e9b\u4ec0\u4e48\u4e4b\u7c7b\r\n\uff082\uff09\u5e94\u7528:\r\n\r\npackage demo.listener;\r\n\r\nimport javax.servlet.ServletContext;\r\nimport javax.servlet.http.HttpSessionAttributeListener;\r\nimport javax.servlet.http.HttpSessionBindingEvent;\r\n\r\npublic class UserCounter implements HttpSessionAttributeListener {\r\n\r\npublic void attributeAdded(HttpSessionBindingEvent event) {\r\nif (attributeIsUser(event))\r\n    adjustUserCounter(event.getSession( ).getServletContext( ),\r\n    true);\r\n}\r\n\r\npublic void attributeRemoved(HttpSessionBindingEvent event) {\r\nif (attributeIsUser(event))\r\n    adjustUserCounter(event.getSession( ).getServletContext( ),\r\n    false);\r\n}\r\n\r\npublic void attributeReplaced(HttpSessionBindingEvent event) {\r\n}\r\n\r\nprivate boolean attributeIsUser(HttpSessionBindingEvent event) {\r\nString name = event.getName( );\r\nObject value = event.getValue( );\r\nreturn \"user\".equals(name) &amp;&amp;\r\n       value instanceof demo.app.domain.user;\r\n}\r\n\r\nprivate void adjustUserCounter(ServletContext ctx, boolean userAdded) {\r\nInteger counterObj = (Integer) ctx.getAttribute(\"numUsers\");\r\nint counter = (counterObj == null ? 0 : counterObj.intValue( ));\r\nif (userAdded) {\r\n  counter++;\r\n}\r\nelse {\r\n    if (counter &gt; 0) counter--;\r\n}\r\nctx.setAttribute(\"numUsers\", new Integer(counter));\r\n}\r\n}\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>\u5e38\u7528\u7684listener\u6709\uff1a \uff081\uff09 ServletContextListener \u76d1\u542cServletConte [&hellip;]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[28],"tags":[],"class_list":["post-949","post","type-post","status-publish","format-standard","hentry","category-ssh"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/enjoyasp.net\/index.php\/wp-json\/wp\/v2\/posts\/949","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/enjoyasp.net\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/enjoyasp.net\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/enjoyasp.net\/index.php\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/enjoyasp.net\/index.php\/wp-json\/wp\/v2\/comments?post=949"}],"version-history":[{"count":0,"href":"https:\/\/enjoyasp.net\/index.php\/wp-json\/wp\/v2\/posts\/949\/revisions"}],"wp:attachment":[{"href":"https:\/\/enjoyasp.net\/index.php\/wp-json\/wp\/v2\/media?parent=949"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/enjoyasp.net\/index.php\/wp-json\/wp\/v2\/categories?post=949"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/enjoyasp.net\/index.php\/wp-json\/wp\/v2\/tags?post=949"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}