Use Java bundled with Android Studio for gradle (#8965)

* Use Java bundled with Android Studio for gradle

* review comments

packages/flutter_tools/lib/src/android/android_studio.dart

@@ -5,6 +5,7 @@
 import '../base/common.dart';
 import '../base/context.dart';
 import '../base/file_system.dart';
+import '../base/io.dart';
 import '../base/os.dart';
 import '../base/platform.dart';
 import '../base/process_manager.dart';
@@ -45,6 +46,8 @@ String get gradleExecutable {
   return androidStudio?.gradleExecutable ?? os.which('gradle')?.path;
 }
 
+String get javaPath => androidStudio?.javaPath;
+
 class AndroidStudio implements Comparable<AndroidStudio> {
   AndroidStudio(this.directory, {Version version, this.configured})
       : this.version = version ?? Version.unknown {
@@ -56,6 +59,7 @@ class AndroidStudio implements Comparable<AndroidStudio> {
   final String configured;
 
   String _gradlePath;
+  String _javaPath;
   bool _isValid = false;
   List<String> _validationMessages = <String>[];
 
@@ -99,6 +103,8 @@ class AndroidStudio implements Comparable<AndroidStudio> {
   String get gradleExecutable => fs.path
       .join(_gradlePath, 'bin', platform.isWindows ? 'gradle.bat' : 'gradle');
 
+  String get javaPath => _javaPath;
+
   bool get isValid => _isValid;
 
   List<String> get validationMessages => _validationMessages;
@@ -272,6 +278,19 @@ class AndroidStudio implements Comparable<AndroidStudio> {
       _validationMessages.add(
           'Gradle version $latestGradleVersion at $_gradlePath is not executable.');
     }
+
+    final String javaPath = platform.isMacOS ?
+        fs.path.join(directory, 'jre', 'jdk', 'Contents', 'Home') :
+        fs.path.join(directory, 'jre');
+    final ProcessResult result = processManager.runSync(<String>[fs.path.join(javaPath, 'bin', 'java'), '-version']);
+    if (result.exitCode == 0) {
+      final List<String> versionLines = result.stderr.split('\n');
+      final String javaVersion = versionLines.length >= 2 ? versionLines[1] : versionLines[0];
+      _validationMessages.add('Java version: $javaVersion');
+      _javaPath = javaPath;
+    } else {
+      _validationMessages.add('Unable to find bundled Java version.');
+    }
   }
 
   @override

packages/flutter_tools/lib/src/android/android_workflow.dart

@@ -13,6 +13,7 @@ import '../base/process_manager.dart';
 import '../doctor.dart';
 import '../globals.dart';
 import 'android_sdk.dart';
+import 'android_studio.dart' as android_studio;
 
 class AndroidWorkflow extends DoctorValidator implements Workflow {
   AndroidWorkflow() : super('Android toolchain - develop for Android devices');
@@ -30,9 +31,12 @@ class AndroidWorkflow extends DoctorValidator implements Workflow {
   static const String _kJavaExecutable = 'java';
   static const String _kJdkDownload = 'https://www.oracle.com/technetwork/java/javase/downloads/';
 
-  /// First sniff JAVA_HOME, then fallback to PATH.
+  /// First try Java bundled with Android Studio, then sniff JAVA_HOME, then fallback to PATH.
   String _findJavaBinary() {
 
+    if (android_studio.javaPath != null)
+      return fs.path.join(android_studio.javaPath, 'bin', 'java');
+
     final String javaHomeEnv = platform.environment[_kJavaHomeEnvironmentVariable];
     if (javaHomeEnv != null) {
       // Trust JAVA_HOME.

packages/flutter_tools/lib/src/android/gradle.dart

@@ -76,6 +76,7 @@ String get gradleAppOutDirV2 {
       <String>[gradle, 'app:properties'],
       workingDirectory: 'android',
       hideStdout: true,
+      environment: _gradleEnv,
     );
     String buildDir = properties
         .split('\n')
@@ -179,7 +180,8 @@ Future<Null> buildGradleProjectV1(String gradle) async {
   final int exitcode = await runCommandAndStreamOutput(
     <String>[fs.file(gradle).absolute.path, 'build'],
     workingDirectory: 'android',
-    allowReentrantFlutter: true
+    allowReentrantFlutter: true,
+    environment: _gradleEnv,
   );
   status.stop();
 
@@ -214,7 +216,8 @@ Future<Null> buildGradleProjectV2(String gradle, String buildModeName, String ta
   final int exitcode = await runCommandAndStreamOutput(
       command,
       workingDirectory: 'android',
-      allowReentrantFlutter: true
+      allowReentrantFlutter: true,
+      environment: _gradleEnv,
   );
   status.stop();
 
@@ -233,3 +236,12 @@ Future<Null> buildGradleProjectV2(String gradle, String buildModeName, String ta
 
   printStatus('Built ${apkFile.path} (${getSizeAsMB(apkFile.lengthSync())}).');
 }
+
+Map<String, String> get _gradleEnv {
+  final Map<String, String> env = new Map<String, String>.from(platform.environment);
+  if (javaPath != null) {
+    // Use java bundled with Android Studio.
+    env['JAVA_HOME'] = javaPath;
+  }
+  return env;
+}