I have a gradle project in my Eclipse with a number of spring-integration context XMLs. These context XML files used to validate okay against the spring-integration schemas
Here is an answer: http://forum.spring.io/forum/spring-projects/integration/738046-eclipse-cannot-find-the-spring-integration-3-0-xsd-and-fails-validation
Quote Gary:
If you enable "Spring Nature" on the project, STS should resolve the schemas from the jars.