tomcat7.0.63之前：
| maxPostSize | The maximum size in bytes of the POST which will be handled by the container FORM URL parameter parsing. The limit can be disabled by setting this attribute to a value less than or equal to 0. If not specified, this attribute is set to 2097152 (2 megabytes). |
设置为0和负数均可以代表不限制
tomcat7.0.63（包含）之后：
| maxPostSize | The maximum size in bytes of the POST which will be handled by the container FORM URL parameter parsing. The limit can be disabled by setting this attribute to a value less than zero. If not specified, this attribute is set to 2097152 (2 megabytes). |
不可以设置为0，只能是负数代表不限制