引言：在高并發下限制最大并發次數，在web.xml中用過濾器設置參數（最大并發數），并設置其他相關參數。詳細見代碼。
第一步：配置web.xml配置，不懂的地方解釋一下：參數50通過參數名maxConcurrent用在filter的實現類中獲取，filter-class就是寫的實現類，
url-pattern就是限制并發時間的url，結束！
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<filter> <filter-name>ConcurrentCountFilter</filter-name> <filter-class>com.procure.pass.ConcurrentCountFilter</filter-class> <init-param> <param-name>maxConcurrent</param-name> <param-value>50</param-value> </init-param> </filter> <filter-mapping> <filter-name>ConcurrentCountFilter</filter-name> <url-pattern>/a/pass/export</url-pattern> </filter-mapping> |
第二步：寫實現類實現filter，該接口有三個方法，詳見代碼。
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import java.io.IOException; import java.util.concurrent.atomic.AtomicInteger; 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.HttpServletResponse; import org.slf4j.Logger; import org.slf4j.LoggerFactory; /** * Servlet Filter implementation class ConcurrentCountFilter */public class ConcurrentCountFilter implements Filter { private static Logger log = LoggerFactory.getLogger(ConcurrentCountFilter.class); private FilterConfig filterConfig; private int maxConcurrent = -1; //總計數 private static AtomicInteger count = new AtomicInteger(0); /** * 獲取當前并發數 * @return */ public static int get(){ return count.get(); } /** * 增加并發數量 * @return */ public static int increase(){ return count.incrementAndGet(); } /** * 減少并發數量 * @return */ public static int decrement(){ return count.decrementAndGet(); } /** * 初始化 */ public void init(FilterConfig filterConfig) throws ServletException { //獲取配置的最大并發數量 String maxStr = filterConfig.getInitParameter("maxConcurrent"); int num = -1; if(maxStr != null && !"".equals(maxStr)){ num = Integer.parseInt(maxStr); } if(num >= 1){ this.maxConcurrent = num; }else{ this.maxConcurrent = -1; } } /** * 過濾主方法 */ public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { try{ //增加并發數量 int num = increase(); if(maxConcurrent > 0){ if(maxConcurrent >= num){ chain.doFilter(request, response); log.info("第一次并發數量："+count.get()); }else{ HttpServletResponse res = (HttpServletResponse) response; res.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,"達到最大并發數限制"); log.info("達到最大并發數"); log.info("最大并發數量："+count.get()); } }else{ chain.doFilter(request, response); log.info("第二次并發數量："+count.get()); } }finally { decrement(); log.info("減小的并發量："+count.get()); } } /** * 退出銷毀 */ public void destroy() { this.filterConfig = null; log.info("銷毀......"); } } |
代碼到此完。
吐槽一下自己在項目中遇到的坑：
1.response.sendError( int, string);在本文代碼中為res.sendError其中若直接如本文代碼那樣會返回一個503服務器帶出來的頁面，此頁面粗暴及其難看，
在此為了友好通知用戶，需做如下步驟，在web.xml中做如下配置代碼：
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<error-page> <error-code>503</error-code> <location>/WEB-INF/views/error/503.jsp</location> </error-page> |
如果在web.xml中配置了上面信息，首先會過濾503(HttpServletResponse.SC_SERVICE_UNAVAILABLE)狀態碼下的此頁面而不會拋服務器的頁面。
其中503.jsp頁面需自己完成在此僅僅貼出來一個示例做參考，代碼如下：
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<% response.setStatus(503); // 獲取異常類 Throwable ex = Exceptions.getThrowable(request); if (ex != null){ LoggerFactory.getLogger("500.jsp").error(ex.getMessage(), ex); } // 編譯錯誤信息 StringBuilder sb = new StringBuilder("錯誤信息：\n"); if (ex != null) { sb.append(Exceptions.getStackTraceAsString(ex)); } else { sb.append("未知錯誤.\n\n"); } // 如果是異步請求或是手機端，則直接返回信息 if (Servlets.isAjaxRequest(request)) { out.print(sb); } // 輸出異常信息頁面 else { %> <%@page import="org.slf4j.Logger,org.slf4j.LoggerFactory"%> <%@page import="com.xahl_oa.internal.common.web.Servlets"%> <%@page import="com.xahl_oa.internal.common.utils.Exceptions"%> <%@page import="com.xahl_oa.internal.common.utils.StringUtils"%> <%@page contentType="text/html;charset=UTF-8" isErrorPage="true"%> <%@include file="/WEB-INF/views/include/taglib.jsp"%> <!DOCTYPE html> <html> <head> <title>503 - 服務暫時不可用</title> <%@include file="/WEB-INF/views/include/head.jsp" %> </head> <body> <div class="container-fluid"> <div class="page-header"><h1>服務暫時不可用請稍后再試.</h1></div> <div class="errorMessage"> 錯誤信息：<%=ex==null?"未知錯誤.":StringUtils.toHtml(ex.getMessage())%> <br/> <br/> 服務器暫時不可用請稍后再試，謝謝！<br/> <br/> <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="history.go(-1);" class="btn">返回上一頁</a> <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="$('.errorMessage').toggle();" class="btn">查看詳細信息</a> </div> <div class="errorMessage hide"> <%=StringUtils.toHtml(sb.toString())%> <br/> <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="history.go(-1);" class="btn">返回上一頁</a> <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="$('.errorMessage').toggle();" class="btn">隱藏詳細信息</a> <br/> <br/> </div> <script>try{top.$.jBox.closeTip();}catch(e){}</script> </div> </body> </html> <% } out = pageContext.pushBody(); %> |
此頁面就比服務器拋出的頁面友好甚多。
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原文鏈接：http://blog.csdn.net/smy_0114/article/details/55270707
