No 'Access-Control-Allow-Origin' header is present on the requested resource.

XMLHttpRequest 를 이용하여 다른 도메인의 서비스를 호출하면 아래와 같은 오류를 직면하게 된다.

XMLHttpRequest cannot load http://example.com/login. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8080' is therefore not allowed access. 

web.xml 에 아래와 같이 필터를 추가하면 개발단계에서는 오류 해결은 가능. 운영 시에는 옵션 조정이 필요할 듯 하다.

<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> <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>

출처: http://tomcat.apache.org/tomcat-7.0-doc/config/filter.html#CORS_Filter