Allow decoding of parameterizedTypes (generics) Fixes #759 (#758)

* Allow decoding of parameterizedTypes (generics)

* Allow decoding of parameterizedTypes (generics)

Author: RicardoRdzG

jaxb/src/main/java/feign/jaxb/JAXBDecoder.java

@@ -18,6 +18,7 @@
 import feign.codec.DecodeException;
 import feign.codec.Decoder;
 import java.io.IOException;
+import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import javax.xml.bind.JAXBException;
 import javax.xml.bind.Unmarshaller;
@@ -35,13 +36,13 @@
  *
  * <pre>
  * JAXBContextFactory jaxbFactory = new JAXBContextFactory.Builder()
- *     .withMarshallerJAXBEncoding("UTF-8")
- *     .withMarshallerSchemaLocation("http://apihost http://apihost/schema.xsd")
+ *     .withMarshallerJAXBEncoding(&quot;UTF-8&quot;)
+ *     .withMarshallerSchemaLocation(&quot;http://apihost http://apihost/schema.xsd&quot;)
  *     .build();
  *
  * api = Feign.builder()
  *     .decoder(new JAXBDecoder(jaxbFactory))
- *     .target(MyApi.class, "http://api");
+ *     .target(MyApi.class, &quot;http://api&quot;);
  * </pre>
  *
  * <p>The JAXBContextFactory should be reused across requests as it caches the created JAXB
@@ -66,6 +67,10 @@ private JAXBDecoder(Builder builder) {
   public Object decode(Response response, Type type) throws IOException {
     if (response.status() == 404) return Util.emptyValueOf(type);
     if (response.body() == null) return null;
+    while (type instanceof ParameterizedType) {
+      ParameterizedType ptype = (ParameterizedType) type;
+      type = ptype.getRawType();
+    }
     if (!(type instanceof Class)) {
       throw new UnsupportedOperationException(
           "JAXB only supports decoding raw types. Found " + type);

jaxb/src/test/java/feign/jaxb/JAXBCodecTest.java

@@ -188,9 +188,11 @@ public void decodesXml() throws Exception {
 
   @Test
   public void doesntDecodeParameterizedTypes() throws Exception {
-    thrown.expect(UnsupportedOperationException.class);
+    thrown.expect(feign.codec.DecodeException.class);
     thrown.expectMessage(
-        "JAXB only supports decoding raw types. Found java.util.Map<java.lang.String, ?>");
+        "java.util.Map is an interface, and JAXB can't handle interfaces.\n"
+            + "\tthis problem is related to the following location:\n"
+            + "\t\tat java.util.Map");
 
     class ParameterizedHolder {
 
@@ -210,6 +212,42 @@ class ParameterizedHolder {
     new JAXBDecoder(new JAXBContextFactory.Builder().build()).decode(response, parameterized);
   }
 
+  @XmlRootElement
+  static class Box<T> {
+
+    @XmlElement private T t;
+
+    public void set(T t) {
+      this.t = t;
+    }
+  }
+
+  @Test
+  public void decodeAnnotatedParameterizedTypes() throws Exception {
+    JAXBContextFactory jaxbContextFactory =
+        new JAXBContextFactory.Builder().withMarshallerFormattedOutput(true).build();
+
+    Encoder encoder = new JAXBEncoder(jaxbContextFactory);
+
+    Box<String> boxStr = new Box<>();
+    boxStr.set("hello");
+    Box<Box<String>> boxBoxStr = new Box<>();
+    boxBoxStr.set(boxStr);
+    RequestTemplate template = new RequestTemplate();
+    encoder.encode(boxBoxStr, Box.class, template);
+
+    Response response =
+        Response.builder()
+            .status(200)
+            .reason("OK")
+            .request(Request.create("GET", "/api", Collections.emptyMap(), null, Util.UTF_8))
+            .headers(Collections.<String, Collection<String>>emptyMap())
+            .body(template.body())
+            .build();
+
+    new JAXBDecoder(new JAXBContextFactory.Builder().build()).decode(response, Box.class);
+  }
+
   /** Enabled via {@link feign.Feign.Builder#decode404()} */
   @Test
   public void notFoundDecodesToEmpty() throws Exception {