查看“Tomcat 最大连接数设置”的源代码

http://tomcat.apache.org/tomcat-7.0-doc/config/http.html

If more simultaneous requests are received than can be handled by the currently available request processing threads, additional threads will be created up to the configured maximum (the value of the maxThreads attribute). If still more simultaneous requests are received, they are stacked up inside the server socket created by the Connector, up to the configured maximum (the value of the acceptCount attribute).

所以需要设置的是maxThreads和acceptCount这两个值：

其中，maxThreads的介绍如下：

The maximum number of request processing threads to be created by this Connector, which therefore determines the maximum number of simultaneous requests that can be handled. If not specified, this attribute is set to 200. If an executor is associated with this connector, this attribute is ignored as the connector will execute tasks using the executor rather than an internal thread pool.

而acceptCount的介绍为：

The maximum queue length for incoming connection requests when all possible request processing threads are in use. Any requests received when the queue is full will be refused. The default value is 100.

所以两者的默认值分别是200和100，要调整Tomcat的默认最大连接数，可以增加这两个属性的值，并且使acceptCount大于等于maxThreads：

 <Connector port="8080" protocol="HTTP/1.1"   
           connectionTimeout="20000"   
           redirectPort="8443" acceptCount="500" maxThreads="400" ></Connector>