Eclipse Gradle build "Could not find tools.jar"

I had the same problem. I believe it is caused by the JRE that gradle is configured to use rather than the eclipse/STS JRE. On my machine, gradle had defaulted to using the wrong JRE. When gradle is installed (even via buildship) it puts a .gradle directory in your home directory (C:/Users/username) on Windows. You can create a gradle.properties file in .gradle and specify the JRE/JDK you want gradle to use as in this example:

org.gradle.java.home=C:/Program Files/Java/jdk1.8.0

This would probably be revealed by using the command line approach recommended by robyjwilkins. It should avoid the need to re-install a JDK.

For more information see https://docs.gradle.org/current/userguide/build_environment.html

OK, I got my problem solved finally. It is very easy, I re-installed the JDK. Somehow the stupid Eclipse (or Gradle plugin, I still not sure which goes wrong) just can't recognize my old JDK path.

After I re-installed JDK (take this chance, I upgrade JDK 7 to 8 also), I don't even need Java_home environment variable, it works.