Reduce garbage with small jackson encoded data (Fixes #4977)

src/main/java/io/vertx/core/buffer/impl/VertxHeapByteBuf.java

@@ -13,17 +13,26 @@
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufAllocator;
 import io.netty.buffer.UnpooledHeapByteBuf;
-import io.netty.buffer.UnpooledUnsafeHeapByteBuf;
 
 /**
  * An un-releasable, un-pooled, un-instrumented heap {@code ByteBuf}.
  */
 final class VertxHeapByteBuf extends UnpooledHeapByteBuf {
 
+ private static final byte[] EMPTY = new byte[0];
+
  public VertxHeapByteBuf(ByteBufAllocator alloc, int initialCapacity, int maxCapacity) {
  super(alloc, initialCapacity, maxCapacity);
  }
 
+ @Override
+ protected byte[] allocateArray(int initialCapacity) {
+ if (initialCapacity == 0) {
+ return EMPTY;
+ }
+ return super.allocateArray(initialCapacity);
+ }
+
  @Override
  public ByteBuf retain(int increment) {
  return this;

src/main/java/io/vertx/core/buffer/impl/VertxUnsafeHeapByteBuf.java

@@ -19,10 +19,20 @@
  */
 final class VertxUnsafeHeapByteBuf extends UnpooledUnsafeHeapByteBuf {
 
+ private static final byte[] EMPTY = new byte[0];
+
  public VertxUnsafeHeapByteBuf(ByteBufAllocator alloc, int initialCapacity, int maxCapacity) {
  super(alloc, initialCapacity, maxCapacity);
  }
 
+ @Override
+ protected byte[] allocateArray(int initialCapacity) {
+ if (initialCapacity == 0) {
+ return EMPTY;
+ }
+ return super.allocateArray(initialCapacity);
+ }
+
  @Override
  public ByteBuf retain(int increment) {
  return this;

src/main/java/io/vertx/core/json/jackson/JacksonCodec.java

@@ -20,9 +20,9 @@
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufInputStream;
 import io.netty.buffer.ByteBufOutputStream;
-import io.netty.buffer.Unpooled;
 import io.vertx.core.buffer.Buffer;
 import io.vertx.core.buffer.impl.BufferInternal;
+import io.vertx.core.buffer.impl.VertxByteBufAllocator;
 import io.vertx.core.json.DecodeException;
 import io.vertx.core.json.EncodeException;
 import io.vertx.core.json.JsonArray;
@@ -105,16 +105,19 @@ public String toString(Object object, boolean pretty) throws EncodeException {
 
  @Override
  public Buffer toBuffer(Object object, boolean pretty) throws EncodeException {
- ByteBuf buf = Unpooled.buffer();
+ // these buffers are not pooled and not instrumented, which make them faster
+ // This can use 0 as initial capacity, because Jackson will flush the tmp encoded buffer in one go, on flush
+ // causing a single resize of the right final size
+ ByteBuf nettyBuffer = VertxByteBufAllocator.DEFAULT.heapBuffer(0, Integer.MAX_VALUE);
  // There is no need to use a try with resources here as jackson
  // is a well-behaved and always calls the closes all streams in the
  // "finally" block bellow.
- ByteBufOutputStream out = new ByteBufOutputStream(buf);
+ ByteBufOutputStream out = new ByteBufOutputStream(nettyBuffer);
  JsonGenerator generator = createGenerator(out, pretty);
  try {
  encodeJson(object, generator);
  generator.flush();
- return BufferInternal.buffer(buf);
+ return BufferInternal.buffer(nettyBuffer);
  } catch (IOException e) {
  throw new EncodeException(e.getMessage(), e);
  } finally {