参考：http://www.cnblogs.com/spring3mvc/archive/2010/11/23/2414741.html
自己写代码经常是顺着逻辑写下去，写完后run一下，ok就玩完事了。直到遇到一个又一个的问题的时候才回头过来重新修改。这就是没有测试的悲剧。因此，在今后的代码中一定要尝试着去写测试，去做测试。
发现Apache Server下有个工具ab可以进行并发请求，正好有个需求想要知道并发下的访问情况。
1.下载
访问：http://httpd.apache.org/download.cgi
然后点击：
然后跳到一个页面说只提供源码，自己编译，云彩。不过也提供了推荐第三方编译，选择第一个：
然后是选择镜像和版本，不要选择德国的：
2.安装
我这是买椟还珠的游戏，不想去了解Apache的功能，只想要ab。所以直接解压，然后在bin目录找到ab就可以了：
3.测试
输入ab就可以看到帮助文档
D:\Java\httpd-2.4.23-x64-vc14\Apache24\bin>ab
ab: wrong number of arguments
Usage: ab [options] [http://]hostname[:port]/path
Options are:
-n requests Number of requests to perform
-c concurrency Number of multiple requests to make at a time
-t timelimit Seconds to max. to spend on benchmarking
This implies -n 50000
-s timeout Seconds to max. wait for each response
Default is 30 seconds
-b windowsize Size of TCP send/receive buffer, in bytes
-B address Address to bind to when making outgoing connections
-p postfile File containing data to POST. Remember also to set -T
-u putfile File containing data to PUT. Remember also to set -T
-T content-type Content-type header to use for POST/PUT data, eg.
'application/x-www-form-urlencoded'
Default is 'text/plain'
-v verbosity How much troubleshooting info to print
-w Print out results in HTML tables
-i Use HEAD instead of GET
-x attributes String to insert as table attributes
-y attributes String to insert as tr attributes
-z attributes String to insert as td or th attributes
-C attribute Add cookie, eg. 'Apache=1234'. (repeatable)
-H attribute Add Arbitrary header line, eg. 'Accept-Encoding: gzip'
Inserted after all normal header lines. (repeatable)
-A attribute Add Basic WWW Authentication, the attributes
are a colon separated username and password.
-P attribute Add Basic Proxy Authentication, the attributes
are a colon separated username and password.
-X proxy:port Proxyserver and port number to use
-V Print version number and exit
-k Use HTTP KeepAlive feature
-d Do not show percentiles served table.
-S Do not show confidence estimators and warnings.
-q Do not show progress when doing more than 150 requests
-l Accept variable document length (use this for dynamic pages)
-g filename Output collected data to gnuplot format file.
-e filename Output CSV file with percentages served
-r Don't exit on socket receive errors.
-m method Method name
-h Display usage information (this message) D:\Java\httpd-2.4.23-x64-vc14\Apache24\bin>
举例：
D:\Java\httpd-2.4.23-x64-vc14\Apache24\bin>ab -n 20 -c 10 localhost:8080/user/all
-n表示一共请求20次
-c表示并发量为10次。
也就是说，会进行两个并发，每次10个。