Sync from google3.

Bug: 68239358
Test: Builds. Tested on device. CTS test passes.

bit FrameworksCoreTests:android.view.textclassifier.TextClassificationManagerTest

Change-Id: Ie5e20b06b1c615ab246e7ed7f08e980e61c492c4
diff --git a/util/java/string_utils.cc b/util/java/string_utils.cc
new file mode 100644
index 0000000..ffd5b11
--- /dev/null
+++ b/util/java/string_utils.cc
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include "util/java/string_utils.h"
+
+#include "util/base/logging.h"
+
+namespace libtextclassifier2 {
+
+bool JStringToUtf8String(JNIEnv* env, const jstring& jstr,
+                         std::string* result) {
+  if (jstr == nullptr) {
+    *result = std::string();
+    return false;
+  }
+
+  jclass string_class = env->FindClass("java/lang/String");
+  if (!string_class) {
+    TC_LOG(ERROR) << "Can't find String class";
+    return false;
+  }
+
+  jmethodID get_bytes_id =
+      env->GetMethodID(string_class, "getBytes", "(Ljava/lang/String;)[B");
+
+  jstring encoding = env->NewStringUTF("UTF-8");
+  jbyteArray array = reinterpret_cast<jbyteArray>(
+      env->CallObjectMethod(jstr, get_bytes_id, encoding));
+
+  jbyte* const array_bytes = env->GetByteArrayElements(array, JNI_FALSE);
+  int length = env->GetArrayLength(array);
+
+  *result = std::string(reinterpret_cast<char*>(array_bytes), length);
+
+  // Release the array.
+  env->ReleaseByteArrayElements(array, array_bytes, JNI_ABORT);
+  env->DeleteLocalRef(array);
+  env->DeleteLocalRef(string_class);
+  env->DeleteLocalRef(encoding);
+
+  return true;
+}
+
+}  // namespace libtextclassifier2