GH-3151: Pull projection logic down to the JSON-specific converter impl

Related to: #3151

The `JacksonProjectingMessageConverter` is based only on JSON format.
Therefore, it is wrong to have its logic involved in the `AbstractJacksonMessageConverter`.

* Pull the `JacksonProjectingMessageConverter` down to the `JacksonJsonMessageConverter`
with respective `convertContent()` override
* Remove unnecessary now `setUseProjectionForInterfaces()` from the `JacksonXmlMessageConverter`

Author: artembilan

spring-amqp/src/main/java/org/springframework/amqp/support/converter/AbstractJacksonMessageConverter.java

@@ -29,7 +29,6 @@
 import tools.jackson.core.JacksonException;
 import tools.jackson.databind.JavaType;
 import tools.jackson.databind.ObjectMapper;
-import tools.jackson.databind.json.JsonMapper;
 
 import org.springframework.amqp.core.Message;
 import org.springframework.amqp.core.MessageProperties;
@@ -80,10 +79,6 @@ public abstract class AbstractJacksonMessageConverter extends AbstractMessageCon
 
 	private JacksonJavaTypeMapper javaTypeMapper = new DefaultJacksonJavaTypeMapper();
 
-	private boolean useProjectionForInterfaces;
-
-	private @Nullable JacksonProjectingMessageConverter projectingConverter;
-
 	private boolean charsetIsUtf8 = true;
 
 	private boolean assumeSupportedContentType = true;
@@ -254,25 +249,6 @@ public void setAlwaysConvertToInferredType(boolean alwaysAttemptConversion) {
 		this.alwaysConvertToInferredType = alwaysAttemptConversion;
 	}
 
-	protected boolean isUseProjectionForInterfaces() {
-		return this.useProjectionForInterfaces;
-	}
-
-	/**
-	 * Set to true to use Spring Data projection to create the object if the inferred
-	 * parameter type is an interface.
-	 * @param useProjectionForInterfaces true to use projection.
-	 */
-	public void setUseProjectionForInterfaces(boolean useProjectionForInterfaces) {
-		this.useProjectionForInterfaces = useProjectionForInterfaces;
-		if (useProjectionForInterfaces) {
-			if (!ClassUtils.isPresent("org.springframework.data.projection.ProjectionFactory", this.classLoader)) {
-				throw new IllegalStateException("'spring-data-commons' is required to use Projection Interfaces");
-			}
-			this.projectingConverter = new JacksonProjectingMessageConverter((JsonMapper) this.objectMapper);
-		}
-	}
-
 	/**
 	 * By default, the supported content type is assumed when there is no contentType
 	 * property, or it is set to the default ('application/octet-stream'). Set to 'false'
@@ -336,7 +312,7 @@ public Object fromMessage(Message message, @Nullable Object conversionHint) thro
 		return encoding;
 	}
 
-	private Object doFromMessage(Message message, @Nullable Object conversionHint, MessageProperties properties,
+	protected Object doFromMessage(Message message, @Nullable Object conversionHint, MessageProperties properties,
 			@Nullable String encoding) {
 
 		try {
@@ -347,18 +323,12 @@ private Object doFromMessage(Message message, @Nullable Object conversionHint, M
 		}
 	}
 
-	@SuppressWarnings("NullAway") // Dataflow analysis limitation
-	private Object convertContent(Message message, @Nullable Object conversionHint, MessageProperties properties,
+	protected Object convertContent(Message message, @Nullable Object conversionHint, MessageProperties properties,
 			@Nullable String encoding) throws IOException {
 
 		Object content = null;
 		JavaType inferredType = this.javaTypeMapper.getInferredType(properties);
-		if (inferredType != null && this.useProjectionForInterfaces && inferredType.isInterface()
-				&& !inferredType.getRawClass().getPackage().getName().startsWith("java.util")) { // List etc
-			content = this.projectingConverter.convert(message, inferredType.getRawClass());
-			properties.setProjectionUsed(true);
-		}
-		else if (inferredType != null && this.alwaysConvertToInferredType) {
+		if (inferredType != null && this.alwaysConvertToInferredType) {
 			content = tryConvertType(message, encoding, inferredType);
 		}
 		if (content == null) {

spring-amqp/src/main/java/org/springframework/amqp/support/converter/JacksonJsonMessageConverter.java

@@ -16,11 +16,17 @@
 
 package org.springframework.amqp.support.converter;
 
+import java.io.IOException;
+
+import org.jspecify.annotations.Nullable;
 import tools.jackson.databind.DeserializationFeature;
+import tools.jackson.databind.JavaType;
 import tools.jackson.databind.MapperFeature;
 import tools.jackson.databind.json.JsonMapper;
 
+import org.springframework.amqp.core.Message;
 import org.springframework.amqp.core.MessageProperties;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.MimeTypeUtils;
 
 /**
@@ -32,6 +38,8 @@
  */
 public class JacksonJsonMessageConverter extends AbstractJacksonMessageConverter {
 
+	private @Nullable JacksonProjectingMessageConverter projectingConverter;
+
 	/**
 	 * Construct with an internal {@link JsonMapper} instance and trusted packed to all ({@code *}).
 	 */
@@ -73,4 +81,44 @@ public JacksonJsonMessageConverter(JsonMapper jsonMapper, String... trustedPacka
 		super(jsonMapper, MimeTypeUtils.parseMimeType(MessageProperties.CONTENT_TYPE_JSON), trustedPackages);
 	}
 
+	/**
+	 * Set to true to use Spring Data projection to create the object if the inferred
+	 * parameter type is an interface.
+	 * @param useProjectionForInterfaces true to use projection.
+	 */
+	public void setUseProjectionForInterfaces(boolean useProjectionForInterfaces) {
+		if (useProjectionForInterfaces) {
+			if (!ClassUtils.isPresent("org.springframework.data.projection.ProjectionFactory", getClassLoader())) {
+				throw new IllegalStateException("'spring-data-commons' is required to use Projection Interfaces");
+			}
+			this.projectingConverter = new JacksonProjectingMessageConverter((JsonMapper) this.objectMapper);
+		}
+	}
+
+	protected boolean isUseProjectionForInterfaces() {
+		return this.projectingConverter != null;
+	}
+
+	@Override
+	protected Object convertContent(Message message, @Nullable Object conversionHint, MessageProperties properties,
+			@Nullable String encoding) throws IOException {
+
+		Object content = null;
+
+		JavaType inferredType = getJavaTypeMapper().getInferredType(properties);
+		if (inferredType != null && this.projectingConverter != null && inferredType.isInterface()
+				&& !inferredType.getRawClass().getPackage().getName().startsWith("java.util")) { // List etc
+
+			content = this.projectingConverter.convert(message, inferredType.getRawClass());
+			properties.setProjectionUsed(true);
+		}
+
+		if (content == null) {
+			return super.convertContent(message, conversionHint, properties, encoding);
+		}
+		else {
+			return content;
+		}
+	}
+
 }

spring-amqp/src/main/java/org/springframework/amqp/support/converter/JacksonXmlMessageConverter.java

@@ -72,9 +72,4 @@ public JacksonXmlMessageConverter(XmlMapper xmlMapper, String... trustedPackages
 		super(xmlMapper, MimeTypeUtils.parseMimeType(MessageProperties.CONTENT_TYPE_XML), trustedPackages);
 	}
 
-	@Override
-	public void setUseProjectionForInterfaces(boolean useProjectionForInterfaces) {
-		throw new UnsupportedOperationException("This converter does not support useProjectionForInterfaces");
-	}
-
 }