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Detailed listener example for J2ee with high concurrency

  • 2020-06-07 04:30:04
  • OfStack

Detailed listener example for J2ee with high concurrency

Introduction: To limit the maximum number of concurrences at high concurrences, set parameters (maximum concurrences) with a filter in web.xml, and set other related parameters. See the code for details.
Step 1: Configure the web.xml configuration

url-pattern is the url that limits concurrency, end! 


<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>

Step 2: Write the implementation class to implement filter, which has three methods, as shown in the code. 


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; 
  // Total number of  
  private static AtomicInteger count = new AtomicInteger(0); 
   
  /** 
   *  Gets the current concurrency value  
   * @return 
   */ 
  public static int get(){  
      return count.get();  
    }  
  /** 
   *  Increase the number of concurrency  
   * @return 
   */ 
   public static int increase(){  
      return count.incrementAndGet();  
    } 
   /** 
   *  Reduce the number of concurrency  
   * @return 
   */ 
   public static int decrement(){ 
     return count.decrementAndGet(); 
   } 
   
    
  /** 
   *  Initialize the  
   */ 
    public void init(FilterConfig filterConfig) throws ServletException { 
      // Gets the maximum number of concurrent configurations  
      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; 
      } 
    } 
    /** 
     *  Filter master method  
     */ 
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { 
      try{ 
      // Increase the number of concurrency  
      int num = increase(); 
      if(maxConcurrent > 0){ 
        if(maxConcurrent >= num){ 
          chain.doFilter(request, response); 
          log.info(" The first 1 Number of secondary concurrences: "+count.get()); 
        }else{ 
          HttpServletResponse res = (HttpServletResponse) response; 
          res.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE," The maximum number of concurrences is reached "); 
          log.info(" Reach the maximum number of concurrences "); 
          log.info(" Maximum number of concurrency: "+count.get()); 
        } 
      }else{ 
        chain.doFilter(request, response); 
        log.info(" The first 2 Number of secondary concurrences: "+count.get()); 
      } 
      }finally { 
        decrement(); 
        log.info(" Reduced concurrency: "+count.get()); 
      } 
     
    } 
  /** 
   *  Exit the destruction  
   */ 
  public void destroy() { 
    this.filterConfig = null; 
    log.info(" The destruction ......"); 
  } 
}

That's it for the code.

Make fun of the potholes you encountered in the project:

1. response. sendError (int string); In this code, it is res.sendError. If it is like this code directly, it will return a page from 503 server, which is very rough and ugly.

To kindly notify users, do the following steps in ES42en.xml: 


<error-page> 
  <error-code>503</error-code> 
  <location>/WEB-INF/views/error/503.jsp</location> 
 </error-page>

If the above information is configured in web.xml, this page under the status code of 503(HttpServletResponse.SC_ES51en_ES52en) is first filtered without throwing the server's page.

The 503.ES56en page needs to be completed by yourself. Here is just one example for reference. The code is as follows: 


<% 
response.setStatus(503); 
 
//  Get exception class  
Throwable ex = Exceptions.getThrowable(request); 
if (ex != null){ 
  LoggerFactory.getLogger("500.jsp").error(ex.getMessage(), ex); 
} 
 
//  Compile error message  
StringBuilder sb = new StringBuilder(" Error message: \n"); 
if (ex != null) { 
  sb.append(Exceptions.getStackTraceAsString(ex)); 
} else { 
  sb.append(" An unknown error .\n\n"); 
} 
 
//  If the request is asynchronous or on the phone, the message is returned  
if (Servlets.isAjaxRequest(request)) { 
  out.print(sb); 
} 
 
//  Output the exception information page  
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 -  The service is temporarily unavailable </title> 
  <%@include file="/WEB-INF/views/include/head.jsp" %> 
</head> 
<body> 
  <div class="container-fluid"> 
    <div class="page-header"><h1> The service is temporarily unavailable. Please try again later .</h1></div> 
    <div class="errorMessage"> 
       Error message: <%=ex==null?" An unknown error .":StringUtils.toHtml(ex.getMessage())%> <br/> <br/> 
       The server is temporarily unavailable, please try again later, thank you! <br/> <br/> 
      <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="history.go(-1);" class="btn"> On the back 1 page </a>  
      <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="$('.errorMessage').toggle();" class="btn"> View details </a> 
    </div> 
    <div class="errorMessage hide"> 
      <%=StringUtils.toHtml(sb.toString())%> <br/> 
      <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="history.go(-1);" class="btn"> On the back 1 page </a>  
      <a href="javascript:" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" onclick="$('.errorMessage').toggle();" class="btn"> Hide details </a> 
      <br/> <br/> 
    </div> 
    <script>try{top.$.jBox.closeTip();}catch(e){}</script> 
  </div> 
</body> 
</html> 
<% 
} out = pageContext.pushBody(); 
%>

This page is much friendlier than the page thrown by the server.

Thank you for reading, I hope to help you, thank you for your support to this site!

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