Allow generics deserialization by JacksonJrDecoder (#2298)

* Allow generics deserialization by JacksonJrDecoder
Fixes #2296

* Update JacksonJrDecoder.java

* Update JacksonCodecTest.java

---------

Co-authored-by: Marvin <velo@users.noreply.github.com>

jackson-jr/src/main/java/feign/jackson/jr/JacksonJrDecoder.java

@@ -93,9 +93,6 @@ public Object decode(Response response, Type type) throws IOException {
   }
 
   protected Transformer findTransformer(Response response, Type type) {
-    if (type instanceof Class) {
-      return (mapper, reader) -> mapper.beanFrom((Class<?>) type, reader);
-    }
     if (type instanceof ParameterizedType) {
       Type rawType = ((ParameterizedType) type).getRawType();
       Type[] parameterType = ((ParameterizedType) type).getActualTypeArguments();
@@ -105,6 +102,11 @@ protected Transformer findTransformer(Response response, Type type) {
       if (rawType.equals(Map.class)) {
         return (mapper, reader) -> mapper.mapOfFrom((Class<?>) parameterType[1], reader);
       }
+      type = rawType;
+    }
+    if (type instanceof Class) {
+      Class<?> clazz = (Class<?>) type;
+      return (mapper, reader) -> mapper.beanFrom(clazz, reader);
     }
     throw new DecodeException(500, "Cannot decode type: " + type.getTypeName(), response.request());
   }

jackson-jr/src/test/java/feign/jackson/jr/JacksonCodecTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 The Feign Authors
+ * Copyright 2012-2024 The Feign Authors
  *
  * 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
@@ -16,8 +16,8 @@
 import static feign.Util.UTF_8;
 import static feign.assertj.FeignAssertions.assertThat;
 import static java.util.Collections.singletonList;
-import static org.assertj.core.api.Assertions.assertThat;
 import java.io.IOException;
+import java.lang.reflect.Type;
 import java.nio.charset.StandardCharsets;
 import java.time.LocalDate;
 import java.util.Arrays;
@@ -29,6 +29,8 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.stream.Stream;
+
 import org.junit.jupiter.api.Test;
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.jr.ob.JSON;
@@ -37,6 +39,9 @@
 import feign.RequestTemplate;
 import feign.Response;
 import feign.Util;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
 class JacksonCodecTest {
 
@@ -289,4 +294,57 @@ void notFoundDecodesToEmpty() throws Exception {
         .build();
     assertThat((byte[]) new JacksonJrDecoder().decode(response, byte[].class)).isEmpty();
   }
+
+  @ParameterizedTest
+  @MethodSource("decodeGenericsArguments")
+  void decodeGenerics(Response response, Type responseType, DataWrapper<?> expectedDataWrapper) throws IOException {
+    assertThat(new JacksonJrDecoder().decode(response, responseType)).isEqualTo(expectedDataWrapper);
+  }
+
+  static class DataWrapper<T> {
+    private T data;
+
+    DataWrapper() {
+    }
+
+    DataWrapper(T data) {
+      this.data = data;
+    }
+
+    public void setData(T data) {
+      this.data = data;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+      if (this == o) return true;
+      if (o == null || getClass() != o.getClass()) return false;
+      DataWrapper<?> that = (DataWrapper<?>) o;
+      return Objects.equals(data, that.data);
+    }
+  }
+
+  static Stream<Arguments> decodeGenericsArguments() {
+    Response.Builder responseBuilder = Response
+        .builder()
+        .request(Request.create(
+            HttpMethod.GET,
+            "/v1/dummy",
+            Collections.emptyMap(),
+            Request.Body.empty(),
+            null
+        ));
+    return Stream.of(
+        Arguments.of(
+            responseBuilder.body("{\"data\":2024}", StandardCharsets.UTF_8).build(),
+            new TypeReference<DataWrapper<Integer>>() {}.getType(),
+            new DataWrapper<>(2024)
+        ),
+        Arguments.of(
+            responseBuilder.body("{\"data\":\"Hello, World!\"}", StandardCharsets.UTF_8).build(),
+            new TypeReference<DataWrapper<String>>() {}.getType(),
+            new DataWrapper<>("Hello, World!")
+        )
+    );
+  }
 }