Reasons: lack of related tomcat runtime class
Solution a: Window - & gt; The Preferences - & gt; Server - & gt; The Runtime Environments
And then click add to choose their own tomcat version click next to select installation package specific path
It is good to finally finish to complete the apply application
Solution 2: right-click the project - & gt; Build Path - & gt; Configure Build Path - & gt; Libraries - & gt; The Add Libraries... -> Server Runtime - & gt; Next
Then choose just configured Server click finish and apply,
This problem should be solved,