引言：在高并发下限制最大并发次数，在web.xml中用过滤器设置参数（最大并发数），并设置其他相关参数。详细见代码。
第一步：配置web.xml配置，不懂的地方解释一下：参数50通过参数名maxConcurrent用在filter的实现类中获取，filter-class就是写的实现类，
url-pattern就是限制并发时间的url，结束！
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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：写实现类实现filter，该接口有三个方法，详见代码。
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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; //总计数 private static AtomicInteger count = new AtomicInteger(0); /** * 获取当前并发数 * @return */ public static int get(){ return count.get(); } /** * 增加并发数量 * @return */ public static int increase(){ return count.incrementAndGet(); } /** * 减少并发数量 * @return */ public static int decrement(){ return count.decrementAndGet(); } /** * 初始化 */ public void init(FilterConfig filterConfig) throws ServletException { //获取配置的最大并发数量 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; } } /** * 过滤主方法 */ public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { try{ //增加并发数量 int num = increase(); if(maxConcurrent > 0){ if(maxConcurrent >= num){ chain.doFilter(request, response); log.info("第一次并发数量："+count.get()); }else{ HttpServletResponse res = (HttpServletResponse) response; res.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,"达到最大并发数限制"); log.info("达到最大并发数"); log.info("最大并发数量："+count.get()); } }else{ chain.doFilter(request, response); log.info("第二次并发数量："+count.get()); } }finally { decrement(); log.info("减小的并发量："+count.get()); } } /** * 退出销毁 */ public void destroy() { this.filterConfig = null; log.info("销毁......"); } } |
代码到此完。
吐槽一下自己在项目中遇到的坑：
1.response.sendError( int, string);在本文代码中为res.sendError其中若直接如本文代码那样会返回一个503服务器带出来的页面，此页面粗暴及其难看，
在此为了友好通知用户，需做如下步骤，在web.xml中做如下配置代码：
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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，首先会过滤503(HttpServletResponse.SC_SERVICE_UNAVAILABLE)状态码下的此页面而不会抛服务器的页面。
其中503.jsp页面需自己完成在此仅仅贴出来一个示例做参考，代码如下：
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<% response.setStatus(503); // 获取异常类 Throwable ex = Exceptions.getThrowable(request); if (ex != null){ LoggerFactory.getLogger("500.jsp").error(ex.getMessage(), ex); } // 编译错误信息 StringBuilder sb = new StringBuilder("错误信息：\n"); if (ex != null) { sb.append(Exceptions.getStackTraceAsString(ex)); } else { sb.append("未知错误.\n\n"); } // 如果是异步请求或是手机端，则直接返回信息 if (Servlets.isAjaxRequest(request)) { out.print(sb); } // 输出异常信息页面 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 - 服务暂时不可用</title> <%@include file="/WEB-INF/views/include/head.jsp" %> </head> <body> <div class="container-fluid"> <div class="page-header"><h1>服务暂时不可用请稍后再试.</h1></div> <div class="errorMessage"> 错误信息：<%=ex==null?"未知错误.":StringUtils.toHtml(ex.getMessage())%> <br/> <br/> 服务器暂时不可用请稍后再试，谢谢！<br/> <br/> <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="history.go(-1);" class="btn">返回上一页</a> <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="$('.errorMessage').toggle();" class="btn">查看详细信息</a> </div> <div class="errorMessage hide"> <%=StringUtils.toHtml(sb.toString())%> <br/> <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="history.go(-1);" class="btn">返回上一页</a> <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="$('.errorMessage').toggle();" class="btn">隐藏详细信息</a> <br/> <br/> </div> <script>try{top.$.jBox.closeTip();}catch(e){}</script> </div> </body> </html> <% } out = pageContext.pushBody(); %> |
此页面就比服务器抛出的页面友好甚多。
感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！
原文链接：http://blog.csdn.net/smy_0114/article/details/55270707
