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!

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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

本文链接:https://my.lmcjl.com/post/18414.html

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