J2ee 高并发情况下监听器实例详解

j2ee 高并发情况下监听器实例详解

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！

<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。

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：

<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：

<% 
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！