Make JDK version check more robust. The current logic could fail due to StringIndexOutOfBoundsException because of calling version.substring(0, -1). The system property "java.version" could be a single integer that does not contain dot. RELNOTES: None PiperOrigin-RevId: 202578981

diff --git a/src/main/java/com/google/devtools/build/lib/unsafe/BUILD b/src/main/java/com/google/devtools/build/lib/unsafe/BUILD
index 7c2b208..84feca8 100644
--- a/src/main/java/com/google/devtools/build/lib/unsafe/BUILD
+++ b/src/main/java/com/google/devtools/build/lib/unsafe/BUILD

@@ -14,7 +14,10 @@
 
 java_library(
     name = "string",
-    srcs = ["StringUnsafe.java"],
+    srcs = [
+        "RuntimeVersion.java",
+        "StringUnsafe.java",
+    ],
     deps = [
         ":unsafe-provider",
         "//third_party:guava",

diff --git a/src/main/java/com/google/devtools/build/lib/unsafe/RuntimeVersion.java b/src/main/java/com/google/devtools/build/lib/unsafe/RuntimeVersion.java
new file mode 100644
index 0000000..8c2bb2a
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/unsafe/RuntimeVersion.java

@@ -0,0 +1,49 @@
+// Copyright 2018 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.unsafe;
+
+import java.lang.reflect.Method;
+
+/**
+ * JDK version string utilities.
+ *
+ * <p>Code in this class is copied from Java Platform Team's JDK version string utility class,
+ * in order to avoid exporting an extra dependence from internal repository.
+ */
+final class RuntimeVersion {
+
+  private static final int MAJOR = getMajorJdkVersion();
+
+  private static int getMajorJdkVersion() {
+    try {
+      Method versionMethod = Runtime.class.getMethod("version");
+      Object version = versionMethod.invoke(null);
+      return (int) version.getClass().getMethod("major").invoke(version);
+    } catch (Exception e) {
+      // continue below
+    }
+
+    int version = (int) Double.parseDouble(System.getProperty("java.class.version"));
+    if (49 <= version && version <= 52) {
+      return version - (49 - 5);
+    }
+    throw new IllegalStateException(
+        "Unknown Java version: " + System.getProperty("java.specification.version"));
+  }
+
+  /** Returns true if the current runtime is JDK 9 or newer. */
+  static boolean isAtLeast9() {
+    return MAJOR >= 9;
+  }
+}

diff --git a/src/main/java/com/google/devtools/build/lib/unsafe/StringUnsafe.java b/src/main/java/com/google/devtools/build/lib/unsafe/StringUnsafe.java
index 8701e86..eeaa542 100644
--- a/src/main/java/com/google/devtools/build/lib/unsafe/StringUnsafe.java
+++ b/src/main/java/com/google/devtools/build/lib/unsafe/StringUnsafe.java

@@ -30,8 +30,6 @@
  * <p>The <code>value</code> field contains the actual bytes.
  */
 public class StringUnsafe {
-  private static final boolean CAN_USE = getVersion() > 1.8;
-
   // Fields corresponding to the coder
   public static final byte LATIN1 = 0;
   public static final byte UTF16 = 1;
@@ -43,14 +41,7 @@
   private final long coderOffset;
 
   public static boolean canUse() {
-    return CAN_USE;
-  }
-
-  private static double getVersion() {
-    String version = System.getProperty("java.version");
-    int pos = version.indexOf('.');
-    pos = version.indexOf('.', pos + 1);
-    return Double.parseDouble(version.substring(0, pos));
+    return RuntimeVersion.isAtLeast9();
   }
 
   @Nullable