Fix #315 and #324: add @JsonDeserializeAs, @JsonSerializeAs (#325)

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -18,10 +18,12 @@ NOTE: Jackson 3.x components rely on 2.x annotations; there are no separate
 
 #314: Add `JsonInclude.Value` convenience constants
  (contributed by @runeflobakk)
+#315: Add `@JsonDeserializeAs`
 #316: Make `JsonFormat.Features` java.io.Serializable
  (requested by @tiger9800)
 #320: Add `radix` property to `@JsonFormat` annotation
  (contributed by @tiger9800)
+#324: Add `@JsonSerializeAs`
 - Fix SBOM generation, publishing
 
 2.20 (28-Aug-2025)

src/main/java/com/fasterxml/jackson/annotation/JsonDeserializeAs.java

@@ -0,0 +1,74 @@
+package com.fasterxml.jackson.annotation;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Annotation to indicate override of deserialization target type;
+ * a more specialized type (sub-type) than declared one.
+ * Can be used on types ({@code Class}es) or on properties (property accessors
+ * like "getters", "setters" and constructor parameters).
+ * Overrides can apply to:
+ *<ul>
+ * <li>{@code value} itself (for all types and properties)
+ *  </li>
+ * <li>{@code content} of structured types (array and {@link java.util.Collection}
+ *   elements; {@link java.util.Map} values)
+ *  </li>
+ * <li>{@code key}s of {@link java.util.Map}s
+ *  </li>
+ *<p>
+ * To indicate that no override is to be used, {@code Void.class} is used
+ * as the marker (will use declared type) -- this is necessary as Annotation
+ * properties cannot have {@code null} values.
+ *<p>
+ * Example usage:
+ *<pre>
+ * public class POJO {
+ *   &#64;JsonDeserializeAs(ValueImpl.class)
+ *   public Value value;
+ *
+ *   &#64;JsonDeserializeAs(keys = KeyEnum.class, content = ValueImpl.class)
+ *   public Map&lt;Object, Object> props;
+ * }
+ *</pre>
+ */
+@Target({ElementType.ANNOTATION_TYPE, ElementType.METHOD, ElementType.FIELD,
+    ElementType.TYPE, ElementType.PARAMETER})
+@Retention(RetentionPolicy.RUNTIME)
+@JacksonAnnotation
+public @interface JsonDeserializeAs
+{
+    /**
+     * Type to deserialize values as, instead of type declared.
+     * Must be a sub-type of declared type; otherwise an
+     * exception may be thrown by deserializer.
+     *<p>
+     * Bogus type {@link java.lang.Void} is used to indicate that declared
+     * type is used as-is (i.e. this annotation property has no setting).
+     */
+    public Class<?> value() default Void.class;
+
+    /**
+     * Type to deserialize content entries (array and {@link java.util.Collection}
+     * elements, {@link java.util.Map} values) as, instead of type declared.
+     * Must be a sub-type of declared type; otherwise an
+     * exception may be thrown by deserializer.
+     *<p>
+     * Bogus type {@link java.lang.Void} is used to indicate that declared
+     * type is used as-is (i.e. this annotation property has no setting).
+     */
+    public Class<?> content() default Void.class;
+
+    /**
+     * Type to deserialize {@link java.util.Map} keys as, instead of type declared.
+     * Must be a sub-type of declared type; otherwise an
+     * exception may be thrown by deserializer.
+     *<p>
+     * Bogus type {@link java.lang.Void} is used to indicate that declared
+     * type is used as-is (i.e. this annotation property has no setting).
+     */
+    public Class<?> keys() default Void.class;
+}

src/main/java/com/fasterxml/jackson/annotation/JsonSerializeAs.java

@@ -0,0 +1,75 @@
+package com.fasterxml.jackson.annotation;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Annotation to indicate override of intended serialization type;
+ * a more generic type (super-type) than declared one.
+ * Can be used on types ({@code Class}es) or on properties (property accessors
+ * like "getters", "setters" and constructor parameters).
+ * Overrides can apply to:
+ *<ul>
+ * <li>{@code value} itself (for all types and properties)
+ *  </li>
+ * <li>{@code content} of structured types (array and {@link java.util.Collection}
+ *   elements; {@link java.util.Map} values)
+ *  </li>
+ * <li>{@code key}s of {@link java.util.Map}s
+ *  </li>
+ *<p>
+ * To indicate that no override is to be used, {@code Void.class} is used
+ * as the marker (will use declared type) -- this is necessary as Annotation
+ * properties cannot have {@code null} values.
+ *<p>
+ * Example usage:
+ *<pre>
+ * public class POJO {
+ *   // ValueImpl extends GenericValue
+ *   &#64;JsonSerializeAs(GenericValue.class)
+ *   public ValueImpl value;
+ *
+ *   &#64;JsonSerializeAs(keys = GenericKey.class, content = GenericValue.class)
+ *   public Map&lt;KeyImpl, ValueImpl> props;
+ * }
+ *</pre>
+ */
+@Target({ElementType.ANNOTATION_TYPE, ElementType.METHOD, ElementType.FIELD,
+    ElementType.TYPE, ElementType.PARAMETER})
+@Retention(RetentionPolicy.RUNTIME)
+@JacksonAnnotation
+public @interface JsonSerializeAs
+{
+    /**
+     * Type to serialize values as, instead of type declared.
+     * Must be a super-type of declared type (or type itself); otherwise an
+     * exception may be thrown by serializer.
+     *<p>
+     * Bogus type {@link java.lang.Void} is used to indicate that declared
+     * type is used as-is (i.e. this annotation property has no setting).
+     */
+    public Class<?> value() default Void.class;
+
+    /**
+     * Type to serialize content entries (array and {@link java.util.Collection}
+     * elements, {@link java.util.Map} values) as, instead of type declared.
+     * Must be a super-type of declared type (or type itself); otherwise an
+     * exception may be thrown by serializer.
+     *<p>
+     * Bogus type {@link java.lang.Void} is used to indicate that declared
+     * type is used as-is (i.e. this annotation property has no setting).
+     */
+    public Class<?> content() default Void.class;
+
+    /**
+     * Type to serialize {@link java.util.Map} keys as, instead of type declared.
+     * Must be a super-type of declared type (or type itself); otherwise an
+     * exception may be thrown by serializer.
+     *<p>
+     * Bogus type {@link java.lang.Void} is used to indicate that declared
+     * type is used as-is (i.e. this annotation property has no setting).
+     */
+    public Class<?> key() default Void.class;
+}