For Java 7/8 (with Eclipse) you have to download Demos and Samples separately:
Windows x86: 53.8 MB jdk-8u131-windows-i586-demos.zip
Windows x64: 53.82 MB jdk-8u131-windows-x64-demos.zip
After having downloaded either of the above two that is suitable for you (not necessarily "jdk-8u131", but the up-to-date edition of "jdk" Demos and Samples), unzip it.
In Eclipse, click on the "Project" drop-down menu and go to "Properties".
Select "Java Build Path".
Go to the "Libraries".
Click on the "Add External JARS" button.
Then go to the unzipped "jdk1.8.0_131" folder and choose: sample\jnlp\servlet\jnlp.jar.