fix: recognize @XmlJavaTypeAdapter in JaxbConverterFactory

retrofit-converters/jaxb/src/main/java/retrofit2/converter/jaxb/JaxbConverterFactory.java

@@ -21,6 +21,7 @@
 import javax.xml.bind.JAXBContext;
 import javax.xml.bind.JAXBException;
 import javax.xml.bind.annotation.XmlRootElement;
+import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 import okhttp3.MediaType;
 import okhttp3.RequestBody;
 import okhttp3.ResponseBody;
@@ -59,7 +60,7 @@ private JaxbConverterFactory(@Nullable JAXBContext context) {
       Annotation[] parameterAnnotations,
       Annotation[] methodAnnotations,
       Retrofit retrofit) {
-    if (type instanceof Class && ((Class<?>) type).isAnnotationPresent(XmlRootElement.class)) {
+    if (type instanceof Class && isJaxbAnnotated((Class<?>) type)) {
       return new JaxbRequestConverter<>(contextForType((Class<?>) type), (Class<?>) type);
     }
     return null;
@@ -68,12 +69,17 @@ private JaxbConverterFactory(@Nullable JAXBContext context) {
   @Override
   public @Nullable Converter<ResponseBody, ?> responseBodyConverter(
       Type type, Annotation[] annotations, Retrofit retrofit) {
-    if (type instanceof Class && ((Class<?>) type).isAnnotationPresent(XmlRootElement.class)) {
+    if (type instanceof Class && isJaxbAnnotated((Class<?>) type)) {
       return new JaxbResponseConverter<>(contextForType((Class<?>) type), (Class<?>) type);
     }
     return null;
   }
 
+  private static boolean isJaxbAnnotated(Class<?> type) {
+    return type.isAnnotationPresent(XmlRootElement.class)
+        || type.isAnnotationPresent(XmlJavaTypeAdapter.class);
+  }
+
   private JAXBContext contextForType(Class<?> type) {
     try {
       return context != null ? context : JAXBContext.newInstance(type);

retrofit-converters/jaxb/src/test/java/retrofit2/converter/jaxb/ImmutablePoint.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2024 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package retrofit2.converter.jaxb;
+
+import javax.xml.bind.annotation.XmlElement;
+import javax.xml.bind.annotation.XmlRootElement;
+import javax.xml.bind.annotation.adapters.XmlAdapter;
+import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
+
+/**
+ * An immutable type (no no-arg constructor) that uses {@link XmlJavaTypeAdapter} to participate in
+ * JAXB serialization. This is the pattern documented at
+ * http://blog.bdoughan.com/2010/12/jaxb-and-immutable-objects.html
+ */
+@XmlJavaTypeAdapter(ImmutablePoint.Adapter.class)
+final class ImmutablePoint {
+  final int x;
+  final int y;
+
+  ImmutablePoint(int x, int y) {
+    this.x = x;
+    this.y = y;
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    return o instanceof ImmutablePoint
+        && ((ImmutablePoint) o).x == x
+        && ((ImmutablePoint) o).y == y;
+  }
+
+  @Override
+  public int hashCode() {
+    return 31 * x + y;
+  }
+
+  /** Mutable intermediate type used by JAXB. */
+  @XmlRootElement(name = "point")
+  static final class Mutable {
+    @XmlElement public int x;
+    @XmlElement public int y;
+  }
+
+  static final class Adapter extends XmlAdapter<Mutable, ImmutablePoint> {
+    @Override
+    public ImmutablePoint unmarshal(Mutable v) {
+      return new ImmutablePoint(v.x, v.y);
+    }
+
+    @Override
+    public Mutable marshal(ImmutablePoint v) {
+      Mutable m = new Mutable();
+      m.x = v.x;
+      m.y = v.y;
+      return m;
+    }
+  }
+}

retrofit-converters/jaxb/src/test/java/retrofit2/converter/jaxb/JaxbConverterFactoryTest.java

@@ -185,6 +185,28 @@ public void externalEntity() throws Exception {
     assertThat(server.getRequestCount()).isEqualTo(1);
   }
 
+  @Test
+  public void xmlJavaTypeAdapterIsRecognizedForRequestBody() throws Exception {
+    // A class annotated with @XmlJavaTypeAdapter (without @XmlRootElement) should be recognized
+    // by the factory and result in a non-null converter. Previously the factory only checked for
+    // @XmlRootElement and returned null for such types.
+    JaxbConverterFactory factory = JaxbConverterFactory.create();
+    Retrofit retrofit =
+        new Retrofit.Builder().baseUrl(server.url("/")).addConverterFactory(factory).build();
+    assertThat(retrofit.requestBodyConverter(ImmutablePoint.class, new java.lang.annotation.Annotation[0], new java.lang.annotation.Annotation[0])).isNotNull();
+  }
+
+  @Test
+  public void xmlJavaTypeAdapterIsRecognizedForResponseBody() throws Exception {
+    // A class annotated with @XmlJavaTypeAdapter (without @XmlRootElement) should be recognized
+    // by the factory and result in a non-null converter. Previously the factory only checked for
+    // @XmlRootElement and returned null for such types.
+    JaxbConverterFactory factory = JaxbConverterFactory.create();
+    Retrofit retrofit =
+        new Retrofit.Builder().baseUrl(server.url("/")).addConverterFactory(factory).build();
+    assertThat(retrofit.responseBodyConverter(ImmutablePoint.class, new java.lang.annotation.Annotation[0])).isNotNull();
+  }
+
   @Test
   public void externalDtd() throws Exception {
     server.enqueue(

retrofit-converters/jaxb3/src/main/java/retrofit2/converter/jaxb3/JaxbConverterFactory.java

@@ -18,6 +18,7 @@
 import jakarta.xml.bind.JAXBContext;
 import jakarta.xml.bind.JAXBException;
 import jakarta.xml.bind.annotation.XmlRootElement;
+import jakarta.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Type;
 import javax.annotation.Nullable;
@@ -59,7 +60,7 @@ private JaxbConverterFactory(@Nullable JAXBContext context) {
       Annotation[] parameterAnnotations,
       Annotation[] methodAnnotations,
       Retrofit retrofit) {
-    if (type instanceof Class && ((Class<?>) type).isAnnotationPresent(XmlRootElement.class)) {
+    if (type instanceof Class && isJaxbAnnotated((Class<?>) type)) {
       return new JaxbRequestConverter<>(contextForType((Class<?>) type), (Class<?>) type);
     }
     return null;
@@ -68,12 +69,17 @@ private JaxbConverterFactory(@Nullable JAXBContext context) {
   @Override
   public @Nullable Converter<ResponseBody, ?> responseBodyConverter(
       Type type, Annotation[] annotations, Retrofit retrofit) {
-    if (type instanceof Class && ((Class<?>) type).isAnnotationPresent(XmlRootElement.class)) {
+    if (type instanceof Class && isJaxbAnnotated((Class<?>) type)) {
       return new JaxbResponseConverter<>(contextForType((Class<?>) type), (Class<?>) type);
     }
     return null;
   }
 
+  private static boolean isJaxbAnnotated(Class<?> type) {
+    return type.isAnnotationPresent(XmlRootElement.class)
+        || type.isAnnotationPresent(XmlJavaTypeAdapter.class);
+  }
+
   private JAXBContext contextForType(Class<?> type) {
     try {
       return context != null ? context : JAXBContext.newInstance(type);