导出maven工程遇到的问题，"org.eclipse.wst.validation" has been removed，还以为是工程本身的问题，后来发现是eclipse的问题。
解决办法：你项目的存放文件夹（工作空间）下的隐藏文件.metadata
把D:\kaola\kaolaWorkSpace\.metadata\.plugins\org.eclipse.core.runtime\.settings 下的org.eclipse.wst.validation.prefs 删除就可以了
参考资料：
http://stackoverflow.com/questions/21414565/updating-maven-project-has-encountred
参考以下解决办法，未能解决：
Same probleme here, there the solution I fix it
- Open the
.projectfile with your prefered text editor. - delete the node that is about "org.eclipse.wst.validation"
- Close your project
- Open your project
- Launch Maven Update...
Should be good.
Another way to fix it, if you don't want to change your .project config (or if you had several projects that must be fixed)
- Close your workspace (or eclipse)
-move out <WorkspaceDir>\.metadata\.plugins\org.eclipse.core.resources\.projects from the workspace directory
-reopen you workspace
- close it again
-move back the .projects dir (say yes to replace questions ? )
- open you workspace
- Launch Maven Update
Should be good
参考以下答复，解决问题：
It appears that deleting the file org.eclipse.wst.validation.prefs in the directory .metadata/.plugins/org.eclipse.core.runtime/.settings (default settings for workspace) or .settings in each individual project will cause the settings for validation to be reset to their original settings. You can then use validation without getting error messages and try resetting the options from there. However, I'm not sure what combination of settings would cause the problem to reappear. However, if it does, you can repeat the process.