Release Jackson BufferRecycler to its pool in encoders

spring-web/src/main/java/org/springframework/http/codec/AbstractJacksonEncoder.java

@@ -32,6 +32,7 @@
 import tools.jackson.core.JsonEncoding;
 import tools.jackson.core.JsonGenerator;
 import tools.jackson.core.exc.JacksonIOException;
+import tools.jackson.core.util.BufferRecycler;
 import tools.jackson.core.util.ByteArrayBuilder;
 import tools.jackson.databind.JavaType;
 import tools.jackson.databind.ObjectMapper;
@@ -159,7 +160,8 @@ public Flux<DataBuffer> encode(Publisher<?> inputStream, DataBufferFactory buffe
 				}
 
 				ObjectWriter writer = createObjectWriter(mapper, elementType, mimeType, hintsToUse);
-				ByteArrayBuilder byteBuilder = new ByteArrayBuilder(writer.generatorFactory()._getBufferRecycler());
+				BufferRecycler recycler = writer.generatorFactory()._getBufferRecycler();
+				ByteArrayBuilder byteBuilder = new ByteArrayBuilder(recycler);
 				JsonEncoding encoding = getJsonEncoding(mimeType);
 				JsonGenerator generator = mapper.createGenerator(byteBuilder, encoding);
 				SequenceWriter sequenceWriter = writer.writeValues(generator);
@@ -204,6 +206,11 @@ public Flux<DataBuffer> encode(Publisher<?> inputStream, DataBufferFactory buffe
 							catch (JacksonIOException ex) {
 								logger.error("Could not close Encoder resources", ex);
 							}
+							finally {
+								// Release strictly after the generator and builder are done: the
+								// recycler returns to a concurrent pool and may be reused at once.
+								recycler.releaseToPool();
+							}
 						});
 			}
 			catch (JacksonIOException ex) {
@@ -223,7 +230,8 @@ public DataBuffer encodeValue(Object value, DataBufferFactory bufferFactory,
 
 		ObjectWriter writer = createObjectWriter(mapper, valueType, mimeType, hints);
 
-		ByteArrayBuilder byteBuilder = new ByteArrayBuilder(writer.generatorFactory()._getBufferRecycler());
+		BufferRecycler recycler = writer.generatorFactory()._getBufferRecycler();
+		ByteArrayBuilder byteBuilder = new ByteArrayBuilder(recycler);
 		try {
 			JsonEncoding encoding = getJsonEncoding(mimeType);
 
@@ -249,6 +257,7 @@ public DataBuffer encodeValue(Object value, DataBufferFactory bufferFactory,
 		}
 		finally {
 			byteBuilder.release();
+			recycler.releaseToPool();
 		}
 	}
 

spring-web/src/main/java/org/springframework/http/codec/json/AbstractJackson2Encoder.java

@@ -28,6 +28,7 @@
 import com.fasterxml.jackson.core.JsonEncoding;
 import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.core.util.BufferRecycler;
 import com.fasterxml.jackson.core.util.ByteArrayBuilder;
 import com.fasterxml.jackson.databind.JavaType;
 import com.fasterxml.jackson.databind.ObjectMapper;
@@ -171,7 +172,8 @@ public Flux<DataBuffer> encode(Publisher<?> inputStream, DataBufferFactory buffe
 				}
 
 				ObjectWriter writer = createObjectWriter(mapper, elementType, mimeType, null, hintsToUse);
-				ByteArrayBuilder byteBuilder = new ByteArrayBuilder(writer.getFactory()._getBufferRecycler());
+				BufferRecycler recycler = writer.getFactory()._getBufferRecycler();
+				ByteArrayBuilder byteBuilder = new ByteArrayBuilder(recycler);
 				JsonEncoding encoding = getJsonEncoding(mimeType);
 				JsonGenerator generator = mapper.getFactory().createGenerator(byteBuilder, encoding);
 				SequenceWriter sequenceWriter = writer.writeValues(generator);
@@ -216,6 +218,11 @@ public Flux<DataBuffer> encode(Publisher<?> inputStream, DataBufferFactory buffe
 							catch (IOException ex) {
 								logger.error("Could not close Encoder resources", ex);
 							}
+							finally {
+								// Release strictly after the generator and builder are done: the
+								// recycler returns to a concurrent pool and may be reused at once.
+								recycler.releaseToPool();
+							}
 						});
 			}
 			catch (IOException ex) {
@@ -247,7 +254,8 @@ public DataBuffer encodeValue(Object value, DataBufferFactory bufferFactory,
 			writer = writer.with(filters);
 		}
 
-		ByteArrayBuilder byteBuilder = new ByteArrayBuilder(writer.getFactory()._getBufferRecycler());
+		BufferRecycler recycler = writer.getFactory()._getBufferRecycler();
+		ByteArrayBuilder byteBuilder = new ByteArrayBuilder(recycler);
 		try {
 			JsonEncoding encoding = getJsonEncoding(mimeType);
 
@@ -276,6 +284,7 @@ public DataBuffer encodeValue(Object value, DataBufferFactory bufferFactory,
 		}
 		finally {
 			byteBuilder.release();
+			recycler.releaseToPool();
 		}
 	}
 

spring-web/src/test/java/org/springframework/http/codec/json/JacksonJsonEncoderTests.java

@@ -21,6 +21,7 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import com.fasterxml.jackson.annotation.JsonFilter;
 import com.fasterxml.jackson.annotation.JsonTypeInfo;
@@ -29,6 +30,10 @@
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
+import tools.jackson.core.json.JsonFactory;
+import tools.jackson.core.util.BufferRecycler;
+import tools.jackson.core.util.JsonRecyclerPools;
+import tools.jackson.core.util.RecyclerPool;
 import tools.jackson.databind.SerializationFeature;
 import tools.jackson.databind.json.JsonMapper;
 import tools.jackson.databind.ser.FilterProvider;
@@ -37,6 +42,7 @@
 
 import org.springframework.core.ResolvableType;
 import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DataBufferUtils;
 import org.springframework.core.testfixture.codec.AbstractEncoderTests;
 import org.springframework.http.MediaType;
 import org.springframework.http.codec.json.JacksonViewBean.MyJacksonView1;
@@ -305,6 +311,41 @@ void encodeAscii() {
 		);
 	}
 
+	@Test
+	void releasesBufferRecyclerToPool() {
+		CountingRecyclerPool pool = new CountingRecyclerPool();
+		JsonFactory factory = JsonFactory.builder().recyclerPool(pool).build();
+		JacksonJsonEncoder encoder = new JacksonJsonEncoder(JsonMapper.builder(factory).build());
+
+		Pojo pojo = new Pojo("foo", "bar");
+		ResolvableType type = ResolvableType.forClass(Pojo.class);
+
+		// encodeValue (Mono path)
+		drain(encoder.encode(Mono.just(pojo), this.bufferFactory, type, APPLICATION_JSON, null));
+		// Flux joined into a JSON array (non-streaming path)
+		drain(encoder.encode(Flux.just(pojo, pojo), this.bufferFactory, type, APPLICATION_JSON, null));
+		// Flux with a streaming media type (NDJSON separator path)
+		drain(encoder.encode(Flux.just(pojo, pojo), this.bufferFactory, type, APPLICATION_NDJSON, null));
+
+		// Error termination of the streaming path must still release via doAfterTerminate
+		encoder.encode(Flux.error(new IllegalStateException("boom")), this.bufferFactory, type, APPLICATION_NDJSON, null)
+				.as(StepVerifier::create)
+				.expectError(IllegalStateException.class)
+				.verify();
+
+		assertThat(pool.acquired).hasPositiveValue();
+		assertThat(pool.released).hasValue(pool.acquired.get());
+	}
+
+	private static void drain(Flux<DataBuffer> output) {
+		output.as(StepVerifier::create)
+				.thenConsumeWhile(buffer -> {
+					DataBufferUtils.release(buffer);
+					return true;
+				})
+				.verifyComplete();
+	}
+
 
 	@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
 	private static class ParentClass {
@@ -322,4 +363,26 @@ private static class Bar extends ParentClass {
 	record JacksonFilteredBean(String property1, String property2) {
 	}
 
+	@SuppressWarnings("serial")
+	private static final class CountingRecyclerPool implements RecyclerPool<BufferRecycler> {
+
+		final AtomicInteger acquired = new AtomicInteger();
+
+		final AtomicInteger released = new AtomicInteger();
+
+		private final RecyclerPool<BufferRecycler> delegate = JsonRecyclerPools.newConcurrentDequePool();
+
+		@Override
+		public BufferRecycler acquirePooled() {
+			this.acquired.incrementAndGet();
+			return this.delegate.acquirePooled();
+		}
+
+		@Override
+		public void releasePooled(BufferRecycler recycler) {
+			this.released.incrementAndGet();
+			this.delegate.releasePooled(recycler);
+		}
+	}
+
 }