Clear error when building with java 9

Bug: 71711403
Test: ./gradlew && echo ok
Test: JAVA_HOME=/path/to/java9 ./gradlew && echo failed
Change-Id: Id8cb5e00bfdbb24422ec19a7558ffb54754af4da

1 files changed, 7 insertions, 0 deletions

diff --git a/build.gradle b/build.gradle
index 106d916..083381f 100644
--- a/build.gradle
+++ b/build.gradle
@@ -22,6 +22,13 @@ apply plugin: 'maven'
 group = 'com.android'
 version = '1.0.6'
 
+def currentJvmVersion = org.gradle.api.JavaVersion.current()
+if (currentJvmVersion.getMajorVersion() != "8") {
+  throw new Exception("Unsupported java version '" + currentJvmVersion.toString() + "'. Please install java 8.\n" +
+"\n" +
+"If you have already installed java 8, you can instruct Gradle to use it by setting the environment variable JAVA_HOME equal to its file path.")
+}
+
 /*
  * With the build server you are given two env variables:
  * 1. The OUT_DIR is a temporary directory you can use to put things during the build.