Support StringAppendOperator(delimiter_char) constructor in java-api

Summary:
Fixes #3336
Closes https://github.com/facebook/rocksdb/pull/3337

Differential Revision: D7196585

Pulled By: sagar0

fbshipit-source-id: a854f3fc906862ecba685b31946e4ef7c0b421c5

java/rocksjni/merge_operator.cc

@@ -26,12 +26,12 @@
 /*
  * Class:     org_rocksdb_StringAppendOperator
  * Method:    newSharedStringAppendOperator
- * Signature: ()J
+ * Signature: (C)J
  */
 jlong Java_org_rocksdb_StringAppendOperator_newSharedStringAppendOperator
-(JNIEnv* env, jclass jclazz) {
+(JNIEnv* env, jclass jclazz, jchar jdelim) {
   auto* sptr_string_append_op = new std::shared_ptr<rocksdb::MergeOperator>(
-    rocksdb::MergeOperators::CreateFromStringId("stringappend"));
+    rocksdb::MergeOperators::CreateStringAppendOperator((char) jdelim));
   return reinterpret_cast<jlong>(sptr_string_append_op);
 }
 

java/src/main/java/org/rocksdb/StringAppendOperator.java

@@ -11,9 +11,13 @@ package org.rocksdb;
  */
 public class StringAppendOperator extends MergeOperator {
     public StringAppendOperator() {
-        super(newSharedStringAppendOperator());
+        this(',');
     }
 
-    private native static long newSharedStringAppendOperator();
+    public StringAppendOperator(char delim) {
+        super(newSharedStringAppendOperator(delim));
+    }
+
+    private native static long newSharedStringAppendOperator(final char delim);
     @Override protected final native void disposeInternal(final long handle);
 }

utilities/merge_operators.h

@@ -19,6 +19,7 @@ class MergeOperators {
   static std::shared_ptr<MergeOperator> CreateDeprecatedPutOperator();
   static std::shared_ptr<MergeOperator> CreateUInt64AddOperator();
   static std::shared_ptr<MergeOperator> CreateStringAppendOperator();
+  static std::shared_ptr<MergeOperator> CreateStringAppendOperator(char delim_char);
   static std::shared_ptr<MergeOperator> CreateStringAppendTESTOperator();
   static std::shared_ptr<MergeOperator> CreateMaxOperator();
   static std::shared_ptr<MergeOperator> CreateBytesXOROperator();

utilities/merge_operators/string_append/stringappend.cc

@@ -52,4 +52,8 @@ std::shared_ptr<MergeOperator> MergeOperators::CreateStringAppendOperator() {
   return std::make_shared<StringAppendOperator>(',');
 }
 
+std::shared_ptr<MergeOperator> MergeOperators::CreateStringAppendOperator(char delim_char) {
+  return std::make_shared<StringAppendOperator>(delim_char);
+}
+
 } // namespace rocksdb