For editing web.xml old solution will work for 11.1.1.7 but for 11.1.1.8 you can use this solution.You should use WebCenter Portal Server Extension.
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This template will create two projects (that can be named during the creation).
PortalExtension: To add custom code, task flows and beans to WebCenter Spaces.
PortalSharedLibrary: Similar to the former WebCenterSpacesExtensionLibrary; however, deployments are now done using JDeveloper Deployment tools and the versioning is managed by manually modifying MANIFEST.MF
Taking a look into PortalSharedLibrary it contains only a MANIFEST.MF file used for versioning of deployments.
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Where are weblogic.xml and web.xml descriptor?
These files should be generated manually.
To create a weblogic.xml create it as New WebLogic Deployment Descriptor.
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In case of web.xml create it as New Java EE Deployment Descriptor:
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By default, web.xml and weblogic.xml will be part of the deployment. It shouldn’t be configured at the deployment profile.
Now deploy as shared lib in WC_Spaces. It will overwrite extens.spaces.webapp shared lib then restart server. Changes will reflect
Thanks. Happy Coding with Vinay.