I have the latest STS4. I am using installed java-1.8 JDK not embedded as the execution environment. My project just runs fine without any issue.
Ho
Don't spend too much time looking for tools.jar. If you get an error like that, don't be upset.
If you already have java JDK1.8, go to its lib folder, tools.jar should be available there. Copy and paste the same in JRE1.8 lib folder.