The idea is to provide completion in Java Editor, Xml editor and property field (and YAML editor? and other web editors?)

Technical proposal: use the Language Server Protocol

We can define the Language Server one time and then plug it to all editors.
It should be easy to plug to all IDEs/editors supporting the LSP.
For Eclipse , there are extension points for xml and java editor. The Yaml editor might rely on web tools platform sse, so then also have the extension point available.