Add custom deserializers support to AbstractJackson2Decoder

Issue: SPR-15975

spring-web/src/test/java/org/springframework/http/codec/json/Jackson2JsonDecoderTests.java

@@ -16,12 +16,19 @@
 
 package org.springframework.http.codec.json;
 
+import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
+import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
 import org.junit.Test;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -32,6 +39,7 @@ import org.springframework.core.codec.CodecException;
 import org.springframework.core.codec.DecodingException;
 import org.springframework.core.io.buffer.AbstractDataBufferAllocatingTestCase;
 import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DefaultDataBufferFactory;
 import org.springframework.http.codec.Pojo;
 import org.springframework.util.MimeType;
 
@@ -210,6 +218,19 @@ public class Jackson2JsonDecoderTests extends AbstractDataBufferAllocatingTestCa
 		StepVerifier.create(flux).verifyError(CodecException.class);
 	}
 
+	@Test  // SPR-15975
+	public void  customDeserializer() {
+		DataBuffer buffer = new DefaultDataBufferFactory().wrap("{\"test\": 1}".getBytes());
+
+		Jackson2JsonDecoder decoder = new Jackson2JsonDecoder(new ObjectMapper());
+		Flux<TestObject> decoded = decoder.decode(Mono.just(buffer),
+				ResolvableType.forClass(TestObject.class), null, null).cast(TestObject.class);
+
+		StepVerifier.create(decoded)
+				.assertNext(v -> assertEquals(1, v.getTest()))
+				.verifyComplete();
+	}
+
 
 	private static class BeanWithNoDefaultConstructor {
 
@@ -232,4 +253,33 @@ public class Jackson2JsonDecoderTests extends AbstractDataBufferAllocatingTestCa
 
 	}
 
+	@JsonDeserialize(using = Deserializer.class)
+	public static class TestObject {
+		private int test;
+		public int getTest() {
+			return test;
+		}
+		public void setTest(int test) {
+			this.test = test;
+		}
+	}
+
+	public static class Deserializer extends StdDeserializer<TestObject> {
+
+		private static final long serialVersionUID = 1L;
+
+		protected Deserializer() {
+			super(TestObject.class);
+		}
+
+		@Override
+		public TestObject deserialize(JsonParser p,
+				DeserializationContext ctxt) throws IOException, JsonProcessingException {
+			JsonNode node = p.readValueAsTree();
+			TestObject result = new TestObject();
+			result.setTest(node.get("test").asInt());
+			return result;
+		}
+	}
+
 }