Gradle building encoding problem

I use the IDEA of jetbrain.
I encouraged a problem.
when i click refresh button to build project with gradle,my comment of chinses words will be replaced by “???”.
I don’t know how to set file encoding.
I tried to set project default encoding with UTF-8 in IDEA preference,
and tried to set DEFAULT_JVM_OPTS="-Dfile.encoding=UTF-8" in ${GRADLE_HOME}/bin/libexec/gradle,
and tried to write following config in build.gradle:
tasks.withType(JavaCompile) {
options.encoding = “UTF-8”
but these were not effective.
the encoding of file always be ISO-8859-1.
anyone know how to resolve this problem?