JCBC-1062: Optimize LegacyTranscoder encoding for strings

Motivation
----------
The LegacyTranscoder still uses the slower JVM-based encoding for
strings and it rather should use the same optimized encoding
path which we use for RawJsonDocument and others.

Modifications
-------------
This code adds a "fastpath" for the string encoding and moves
all the other options into a nested else block so that the buffer
is only allocated if needed (and not twice w/ overridden by the
optimized method).

Result
------
Faster encoding for the string path.

Change-Id: Id67e7f7b905491b3bb5be5f1bf0552a3fd264b79
Reviewed-on: http://review.couchbase.org/75774
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Michael Nitschinger <michael@nitschinger.at>
Reviewed-by: Subhashni Balakrishnan <b.subhashni@gmail.com>

src/main/java/com/couchbase/client/java/transcoder/LegacyTranscoder.java

@@ -141,38 +141,42 @@ protected Tuple2<ByteBuf, Integer> doEncode(LegacyDocument document)
 
         int flags = 0;
         Object content = document.content();
-        ByteBuf encoded = Unpooled.buffer();
 
+        ByteBuf encoded;
         if (content instanceof String) {
-            encoded.writeBytes(((String) content).getBytes(CharsetUtil.UTF_8));
-        } else if (content instanceof Long) {
-            flags |= SPECIAL_LONG;
-            encoded.writeBytes(encodeNum((Long) content, 8));
-        } else if (content instanceof Integer) {
-            flags |= SPECIAL_INT;
-            encoded.writeBytes(encodeNum((Integer) content, 4));
-        } else if (content instanceof Boolean) {
-            flags |= SPECIAL_BOOLEAN;
-            boolean b = (Boolean) content;
-            encoded = Unpooled.buffer().writeByte(b ? '1' : '0');
-        } else if (content instanceof Date) {
-            flags |= SPECIAL_DATE;
-            encoded.writeBytes(encodeNum(((Date) content).getTime(), 8));
-        } else if (content instanceof Byte) {
-            flags |= SPECIAL_BYTE;
-            encoded.writeByte((Byte) content);
-        } else if (content instanceof Float) {
-            flags |= SPECIAL_FLOAT;
-            encoded.writeBytes(encodeNum(Float.floatToRawIntBits((Float) content), 4));
-        } else if (content instanceof Double) {
-            flags |= SPECIAL_DOUBLE;
-            encoded.writeBytes(encodeNum(Double.doubleToRawLongBits((Double) content), 8));
-        } else if (content instanceof byte[]) {
-            flags |= SPECIAL_BYTEARRAY;
-            encoded.writeBytes((byte[]) content);
+            encoded = TranscoderUtils.encodeStringAsUtf8((String) content);
         } else {
-            flags |= SERIALIZED;
-            encoded.writeBytes(serialize(content));
+            encoded = Unpooled.buffer();
+
+            if (content instanceof Long) {
+                flags |= SPECIAL_LONG;
+                encoded.writeBytes(encodeNum((Long) content, 8));
+            } else if (content instanceof Integer) {
+                flags |= SPECIAL_INT;
+                encoded.writeBytes(encodeNum((Integer) content, 4));
+            } else if (content instanceof Boolean) {
+                flags |= SPECIAL_BOOLEAN;
+                boolean b = (Boolean) content;
+                encoded = Unpooled.buffer().writeByte(b ? '1' : '0');
+            } else if (content instanceof Date) {
+                flags |= SPECIAL_DATE;
+                encoded.writeBytes(encodeNum(((Date) content).getTime(), 8));
+            } else if (content instanceof Byte) {
+                flags |= SPECIAL_BYTE;
+                encoded.writeByte((Byte) content);
+            } else if (content instanceof Float) {
+                flags |= SPECIAL_FLOAT;
+                encoded.writeBytes(encodeNum(Float.floatToRawIntBits((Float) content), 4));
+            } else if (content instanceof Double) {
+                flags |= SPECIAL_DOUBLE;
+                encoded.writeBytes(encodeNum(Double.doubleToRawLongBits((Double) content), 8));
+            } else if (content instanceof byte[]) {
+                flags |= SPECIAL_BYTEARRAY;
+                encoded.writeBytes((byte[]) content);
+            } else {
+                flags |= SERIALIZED;
+                encoded.writeBytes(serialize(content));
+            }
         }
 
         if (encoded.readableBytes() >= compressionThreshold) {