SpringMVC解决跨域问题，以及跨服务器调用时候session丢失的问题总结！！！
从2个方面解决
1：web.xml配置中加上
<filter>
<filter-name>CorsFilter</filter-name>
<filter-class>org.apache.catalina.filters.CorsFilter</filter-class>
<init-param>
<param-name>cors.allowed.origins</param-name>
<param-value>*</param-value>
</init-param>
<init-param>
<param-name>cors.allowed.methods</param-name>
<param-value>GET,POST,HEAD,OPTIONS,PUT</param-value>
</init-param>
<init-param>
<param-name>cors.allowed.headers</param-name>
<param-value>Content-Type,X-Requested-With,accept,Origin,Access-Control-Request-Method,Access-Control-Request-Headers</param-value>
</init-param>
<init-param>
<param-name>cors.exposed.headers</param-name>
<param-value>Access-Control-Allow-Origin,Access-Control-Allow-Credentials</param-value>
</init-param>
<!-- 此处一定要这样设置，而且对应的客户端也要设置xhrFields:{withCredentials:true},否则session将失去 -->
<init-param> <param-name>cors.support.credentials</param-name> <param-value>true</param-value> </init-param>
<init-param>
<param-name>cors.preflight.maxage</param-name>
<param-value>10</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>CorsFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
```
注意：最主要的是cors.support.credentials设置为true
2：jquey在使用ajax的时候一定要设置
xhrFields:{withCredentials:true}
然后其他的都是一样
