Remove unnessecary java.util.List expense in JNI

java/rocksjni/options.cc

@@ -1081,21 +1081,19 @@ jbyte Java_org_rocksdb_Options_compressionType(
  * vector.
  */
 std::vector<rocksdb::CompressionType> rocksdb_compression_vector_helper(
-    JNIEnv* env, jobject jcompressionLevels) {
+    JNIEnv* env, jbyteArray jcompressionLevels) {
   std::vector<rocksdb::CompressionType> compressionLevels;
-  // iterate over compressionLevels
+  
-  jobject iteratorObj = env->CallObjectMethod(
+  jsize len = env->GetArrayLength(jcompressionLevels);
-        jcompressionLevels, rocksdb::ListJni::getIteratorMethod(env));
+  jbyte* jcompressionLevel = env->GetByteArrayElements(jcompressionLevels, NULL);
-  while (env->CallBooleanMethod(
+  for(int i = 0; i < len; i++) {
-    iteratorObj, rocksdb::ListJni::getHasNextMethod(env)) == JNI_TRUE) {
+    jbyte jcl;
-    // get compression
+    jcl = jcompressionLevel[i];
-    jobject jcompression_obj = env->CallObjectMethod(iteratorObj,
+    compressionLevels.push_back(static_cast<rocksdb::CompressionType>(jcl));
-        rocksdb::ListJni::getNextMethod(env));
-    jbyte jcompression = env->CallByteMethod(jcompression_obj,
-        rocksdb::ByteJni::getByteValueMethod(env));
-    compressionLevels.push_back(static_cast<rocksdb::CompressionType>(
-        jcompression));
   }
+  env->ReleaseByteArrayElements(jcompressionLevels, jcompressionLevel,
+      JNI_ABORT);
+
   return compressionLevels;
 }
 
@@ -1103,34 +1101,29 @@ std::vector<rocksdb::CompressionType> rocksdb_compression_vector_helper(
  * Helper method to convert a CompressionType vector to a Java
  * List.
  */
-jobject rocksdb_compression_list_helper(JNIEnv* env,
+jbyteArray rocksdb_compression_list_helper(JNIEnv* env,
     std::vector<rocksdb::CompressionType> compressionLevels) {
-  jclass jListClazz = env->FindClass("java/util/ArrayList");
+  jbyte jbuf[compressionLevels.size()];
-  jmethodID midList = rocksdb::ListJni::getArrayListConstructorMethodId(
-      env, jListClazz);
-  jobject jcompressionLevels = env->NewObject(jListClazz,
-    midList, compressionLevels.size());
-  // insert in java list
   for (std::vector<rocksdb::CompressionType>::size_type i = 0;
         i != compressionLevels.size(); i++) {
-    jclass jByteClazz = env->FindClass("java/lang/Byte");
+      jbuf[i] = compressionLevels[i];
-    jmethodID midByte = env->GetMethodID(jByteClazz, "<init>", "(B)V");
-    jobject obj = env->NewObject(jByteClazz, midByte,
-        compressionLevels[i]);
-    env->CallBooleanMethod(jcompressionLevels,
-        rocksdb::ListJni::getListAddMethodId(env), obj);
   }
+  // insert in java array
+  jbyteArray jcompressionLevels = env->NewByteArray(
+      static_cast<jsize>(compressionLevels.size()));
+  env->SetByteArrayRegion(jcompressionLevels, 0,
+      static_cast<jsize>(compressionLevels.size()), jbuf);
   return jcompressionLevels;
 }
 
 /*
  * Class:     org_rocksdb_Options
  * Method:    setCompressionPerLevel
- * Signature: (JLjava/util/List;)V
+ * Signature: (J[B)V
  */
 void Java_org_rocksdb_Options_setCompressionPerLevel(
     JNIEnv* env, jobject jobj, jlong jhandle,
-    jobject jcompressionLevels) {
+    jbyteArray jcompressionLevels) {
   auto* options = reinterpret_cast<rocksdb::Options*>(jhandle);
   std::vector<rocksdb::CompressionType> compressionLevels =
       rocksdb_compression_vector_helper(env, jcompressionLevels);
@@ -1140,9 +1133,9 @@ void Java_org_rocksdb_Options_setCompressionPerLevel(
 /*
  * Class:     org_rocksdb_Options
  * Method:    compressionPerLevel
- * Signature: (J)Ljava/util/List;
+ * Signature: (J)[B
  */
-jobject Java_org_rocksdb_Options_compressionPerLevel(
+jbyteArray Java_org_rocksdb_Options_compressionPerLevel(
     JNIEnv* env, jobject jobj, jlong jhandle) {
   auto* options = reinterpret_cast<rocksdb::Options*>(jhandle);
   return rocksdb_compression_list_helper(env,
@@ -2285,11 +2278,11 @@ jbyte Java_org_rocksdb_ColumnFamilyOptions_compressionType(
 /*
  * Class:     org_rocksdb_ColumnFamilyOptions
  * Method:    setCompressionPerLevel
- * Signature: (JLjava/util/List;)V
+ * Signature: (J[B)V
  */
 void Java_org_rocksdb_ColumnFamilyOptions_setCompressionPerLevel(
     JNIEnv* env, jobject jobj, jlong jhandle,
-    jobject jcompressionLevels) {
+    jbyteArray jcompressionLevels) {
   auto* options = reinterpret_cast<rocksdb::ColumnFamilyOptions*>(jhandle);
   std::vector<rocksdb::CompressionType> compressionLevels =
       rocksdb_compression_vector_helper(env, jcompressionLevels);
@@ -2299,9 +2292,9 @@ void Java_org_rocksdb_ColumnFamilyOptions_setCompressionPerLevel(
 /*
  * Class:     org_rocksdb_ColumnFamilyOptions
  * Method:    compressionPerLevel
- * Signature: (J)Ljava/util/List;
+ * Signature: (J)[B
  */
-jobject Java_org_rocksdb_ColumnFamilyOptions_compressionPerLevel(
+jbyteArray Java_org_rocksdb_ColumnFamilyOptions_compressionPerLevel(
     JNIEnv* env, jobject jobj, jlong jhandle) {
   auto* options = reinterpret_cast<rocksdb::ColumnFamilyOptions*>(jhandle);
   return rocksdb_compression_list_helper(env,

java/rocksjni/rocksjni.cc

@@ -171,25 +171,21 @@ jlongArray Java_org_rocksdb_RocksDB_open__JLjava_lang_String_2_3_3B_3J(
 /*
  * Class:     org_rocksdb_RocksDB
  * Method:    listColumnFamilies
- * Signature: (JLjava/lang/String;)Ljava/util/List;
+ * Signature: (JLjava/lang/String;)[[B
  */
-jobject Java_org_rocksdb_RocksDB_listColumnFamilies(
+jobjectArray Java_org_rocksdb_RocksDB_listColumnFamilies(
     JNIEnv* env, jclass jclazz, jlong jopt_handle, jstring jdb_path) {
   std::vector<std::string> column_family_names;
-  auto opt = reinterpret_cast<rocksdb::Options*>(jopt_handle);
+  auto* opt = reinterpret_cast<rocksdb::Options*>(jopt_handle);
   const char* db_path = env->GetStringUTFChars(jdb_path, 0);
-  jobject jvalue_list = nullptr;
-
   rocksdb::Status s = rocksdb::DB::ListColumnFamilies(*opt, db_path,
       &column_family_names);
   env->ReleaseStringUTFChars(jdb_path, db_path);
-  if (s.ok()) {
-    // Don't reuse class pointer
-    jclass jListClazz = env->FindClass("java/util/ArrayList");
-    jmethodID mid = rocksdb::ListJni::getArrayListConstructorMethodId(env,
-        jListClazz);
-    jvalue_list = env->NewObject(jListClazz, mid, column_family_names.size());
 
+  jclass jcls_ba = env->FindClass("[B");
+  jobjectArray jresults = env->NewObjectArray(
+      static_cast<jsize>(column_family_names.size()), jcls_ba, NULL);
+  if (s.ok()) {
     for (std::vector<std::string>::size_type i = 0;
         i < column_family_names.size(); i++) {
       jbyteArray jcf_value =
@@ -197,11 +193,11 @@ jobject Java_org_rocksdb_RocksDB_listColumnFamilies(
       env->SetByteArrayRegion(
           jcf_value, 0, static_cast<jsize>(column_family_names[i].size()),
           reinterpret_cast<const jbyte*>(column_family_names[i].data()));
-      env->CallBooleanMethod(jvalue_list,
+      env->SetObjectArrayElement(jresults, static_cast<jsize>(i), jcf_value);
-          rocksdb::ListJni::getListAddMethodId(env), jcf_value);
+      env->DeleteLocalRef(jcf_value);
     }
   }
-  return jvalue_list;
+  return jresults;
 }
 
 //////////////////////////////////////////////////////////////////////////////

java/src/main/java/org/rocksdb/ColumnFamilyOptions.java

@@ -218,10 +218,10 @@ public class ColumnFamilyOptions extends RocksObject
   @Override
   public ColumnFamilyOptions setCompressionPerLevel(
       final List<CompressionType> compressionLevels) {
-    final List<Byte> byteCompressionTypes = new ArrayList<>(
+    final byte[] byteCompressionTypes = new byte[
-        compressionLevels.size());
+        compressionLevels.size()];
-    for (final CompressionType compressionLevel : compressionLevels) {
+    for (int i = 0; i < compressionLevels.size(); i++) {
-      byteCompressionTypes.add(compressionLevel.getValue());
+      byteCompressionTypes[i] = compressionLevels.get(i).getValue();
     }
     setCompressionPerLevel(nativeHandle_, byteCompressionTypes);
     return this;
@@ -229,7 +229,7 @@ public class ColumnFamilyOptions extends RocksObject
 
   @Override
   public List<CompressionType> compressionPerLevel() {
-    final List<Byte> byteCompressionTypes =
+    final byte[] byteCompressionTypes =
         compressionPerLevel(nativeHandle_);
     final List<CompressionType> compressionLevels = new ArrayList<>();
     for (final Byte byteCompressionType : byteCompressionTypes) {
@@ -695,8 +695,8 @@ public class ColumnFamilyOptions extends RocksObject
   private native void setCompressionType(long handle, byte compressionType);
   private native byte compressionType(long handle);
   private native void setCompressionPerLevel(long handle,
-      List<Byte> compressionLevels);
+      byte[] compressionLevels);
-  private native List<Byte> compressionPerLevel(long handle);
+  private native byte[] compressionPerLevel(long handle);
   private native void useFixedLengthPrefixExtractor(
       long handle, int prefixLength);
   private native void useCappedPrefixExtractor(

java/src/main/java/org/rocksdb/Options.java

@@ -679,10 +679,10 @@ public class Options extends RocksObject
 
   @Override
   public Options setCompressionPerLevel(final List<CompressionType> compressionLevels) {
-    final List<Byte> byteCompressionTypes = new ArrayList<>(
+    final byte[] byteCompressionTypes = new byte[
-        compressionLevels.size());
+        compressionLevels.size()];
-    for (final CompressionType compressionLevel : compressionLevels) {
+    for (int i = 0; i < compressionLevels.size(); i++) {
-      byteCompressionTypes.add(compressionLevel.getValue());
+      byteCompressionTypes[i] = compressionLevels.get(i).getValue();
     }
     setCompressionPerLevel(nativeHandle_, byteCompressionTypes);
     return this;
@@ -690,7 +690,7 @@ public class Options extends RocksObject
 
   @Override
   public List<CompressionType> compressionPerLevel() {
-    final List<Byte> byteCompressionTypes =
+    final byte[] byteCompressionTypes =
         compressionPerLevel(nativeHandle_);
     final List<CompressionType> compressionLevels = new ArrayList<>();
     for (final Byte byteCompressionType : byteCompressionTypes) {
@@ -1206,8 +1206,8 @@ public class Options extends RocksObject
   private native void setCompressionType(long handle, byte compressionType);
   private native byte compressionType(long handle);
   private native void setCompressionPerLevel(long handle,
-      List<Byte> compressionLevels);
+      byte[] compressionLevels);
-  private native List<Byte> compressionPerLevel(long handle);
+  private native byte[] compressionPerLevel(long handle);
   private native void useFixedLengthPrefixExtractor(
       long handle, int prefixLength);
   private native void useCappedPrefixExtractor(

java/src/main/java/org/rocksdb/RocksDB.java

@@ -377,7 +377,7 @@ public class RocksDB extends RocksObject {
    */
   public static List<byte[]> listColumnFamilies(final Options options,
       final String path) throws RocksDBException {
-    return RocksDB.listColumnFamilies(options.nativeHandle_, path);
+    return Arrays.asList(RocksDB.listColumnFamilies(options.nativeHandle_, path));
   }
 
   private void storeOptionsInstance(DBOptionsInterface options) {
@@ -1734,7 +1734,7 @@ public class RocksDB extends RocksObject {
       final long[] columnFamilyOptions
   ) throws RocksDBException;
 
-  protected native static List<byte[]> listColumnFamilies(
+  protected native static byte[][] listColumnFamilies(
       long optionsHandle, String path) throws RocksDBException;
   protected native void put(
       long handle, byte[] key, int keyLen,