Is there an integration of any other off line way to get the Java API docs?
If you have no internet connection on your development machine, or if you want to stop the Web traffic for accessing the documentation, you can store the documentation on your local hard drive.
Download header.Window menu, then select Preferences.jre, and then click Installed JREs.java, or another term like jre1.8.0_181.
Standard VM.Edit button.JRE system libraries section, select the library ending with rt.jar, and click the Javadoc Location... button.Javadoc in archive radio button.Archive path field, enter or Browse for your full documentation path (e.g. /home/docs/jdk-8u181-doc.zip).Path within archive field, enter or Browse for the location of the api/index.html file (e.g. docs/api).Validate button to ensure everything is set correctly.OK button, then the Finish button, and finally the Apply & Close button. Your documentation is now linked to the file you specified.