Fixes two bugs related to relationship processing:

- Insures that different relationships that share the same URL result in the resolution of the same object for each relationship
- Insures that encountering the same relationship twice does not prevent the processing of remaining relationships.

Author: emetsger

src/main/java/com/github/jasminb/jsonapi/ResolverState.java

@@ -1,7 +1,9 @@
 package com.github.jasminb.jsonapi;
 
 import java.lang.reflect.Field;
+import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Map;
 import java.util.Set;
 
 /**
@@ -25,6 +27,11 @@ class ResolverState {
      */
     private final Set<String> visited = new HashSet<>();
 
+    /**
+     * Maintains a cache of objects that have been deserialized
+     */
+    private final Map<String, Object> cache = new HashMap<>();
+
     /**
      * Constructs a new state object.
      *
@@ -57,6 +64,20 @@ boolean visited(String url) {
         return !this.visited.add(url);
     }
 
+    Object cache(String url, Object object) {
+        cache.put(url, object);
+        return object;
+    }
+
+    boolean isCached(String url) {
+        return cache.containsKey(url);
+    }
+
+    Object retrieve(String url) {
+        return cache.get(url);
+    }
+
+
     /**
      * Used by the relationship resolution implementation to maintain the relationship type being resolved for this
      * {@code {@link #getField() field}.  Typically "related" or "self".

src/main/java/com/github/jasminb/jsonapi/ResourceConverter.java

@@ -466,23 +466,35 @@ private void handleRelationships(JsonNode source, Object object, Map<String, Obj
 							}
 
 							if (resolverState.visited(link)) {
-								return;
+								if (resolverState.isCached(link)) {
+									relationshipField.set(object, resolverState.retrieve(link));
+								}
+								continue;
 							}
 
 							byte[] content = resolver.resolve(link);
 
 							if (hasResourceLinkage(relationship)) {
+								Object resolvedObject = null;
 								if (isCollection(relationship)) {
-                                    relationshipField.set(object, readObjectCollectionInternal(content, type, resolverState));
-                                } else if (hasResourceLinkage(relationship)) {
-                                    relationshipField.set(object, readObjectInternal(content, type, resolverState));
-                                }
+									resolvedObject = readObjectCollectionInternal(content, type, resolverState);
+									relationshipField.set(object, resolvedObject);
+								} else if (hasResourceLinkage(relationship)) {
+									resolvedObject = readObjectInternal(content, type, resolverState);
+									relationshipField.set(object, resolvedObject);
+								}
+								if (resolvedObject != null) {
+									resolverState.cache(link, resolvedObject);
+								}
 							} else {
 								JsonNode resolvedNode = objectMapper.readTree(content);
+								Object resolvedObject = null;
 								if (ValidationUtils.isCollection(resolvedNode)) {
-									relationshipField.set(object, readObjectCollectionInternal(content, type, resolverState));
+									resolvedObject = readObjectCollectionInternal(content, type, resolverState);
+									relationshipField.set(object, resolvedObject);
 								} else if (ValidationUtils.isObject(resolvedNode)) {
-									relationshipField.set(object, readObjectInternal(content, type, resolverState));
+									resolvedObject = readObjectInternal(content, type, resolverState);
+									relationshipField.set(object, resolvedObject);
 								} else if (ErrorUtils.hasErrors(resolvedNode)){
 									ErrorResponse errors = ErrorUtils.parseError(resolvedNode);
 									StringBuilder msg = new StringBuilder("Unable to parse the response document for " +
@@ -504,6 +516,9 @@ private void handleRelationships(JsonNode source, Object object, Map<String, Obj
 									throw new RuntimeException("Response document for '" + link + "' does not contain" +
 											" primary data.");
 								}
+								if (resolvedObject != null) {
+									resolverState.cache(link, resolvedObject);
+								}
 							}
 						}
 					} else {