GH-2385 - Allow detecting links in embedded documents through HalLinkDiscoverer.

Author: odrotbohm

src/main/java/org/springframework/hateoas/mediatype/hal/HalLinkDiscoverer.java

@@ -21,6 +21,7 @@
 import org.springframework.hateoas.LinkRelation;
 import org.springframework.hateoas.MediaTypes;
 import org.springframework.hateoas.client.JsonPathLinkDiscoverer;
+import org.springframework.hateoas.client.LinkDiscoverer;
 import org.springframework.http.MediaType;
 import org.springframework.util.Assert;
 
@@ -32,6 +33,10 @@
  */
 public class HalLinkDiscoverer extends JsonPathLinkDiscoverer {
 
+	private static final String PATH = "_links..['%s']";
+	private static final String JSON_PATH = "$." + PATH;
+	private static final String RECURSIVE_JSON_PATH = "$.." + PATH;
+
 	/**
 	 * Constructor for {@link MediaTypes#HAL_JSON}.
 	 */
@@ -40,7 +45,25 @@ public HalLinkDiscoverer() {
 	}
 
 	protected HalLinkDiscoverer(MediaType... mediaTypes) {
-		super("$._links..['%s']", mediaTypes);
+		super(JSON_PATH, mediaTypes);
+	}
+
+	/**
+	 * Creates a new {@link LinkDiscoverer} that looks up HAL links in the document recursively. In other words, it also
+	 * finds ones contained in the {@code _embedded} clause.
+	 *
+	 * @return will never be {@literal null}.
+	 * @since 3.0
+	 */
+	public LinkDiscoverer inspectEmbeddeds() {
+
+		return new JsonPathLinkDiscoverer(RECURSIVE_JSON_PATH, mediaTypes.toArray(MediaType[]::new)) {
+
+			@Override
+			protected Link extractLink(Object element, LinkRelation rel) {
+				return HalLinkDiscoverer.this.extractLink(element, rel);
+			}
+		};
 	}
 
 	/*

src/test/java/org/springframework/hateoas/mediatype/hal/HalLinkDiscovererUnitTest.java

@@ -24,7 +24,6 @@
 import org.springframework.hateoas.Link;
 import org.springframework.hateoas.MappingTestUtils;
 import org.springframework.hateoas.MappingTestUtils.ContextualMapper;
-import org.springframework.hateoas.client.LinkDiscoverer;
 import org.springframework.hateoas.client.LinkDiscovererUnitTest;
 
 /**
@@ -35,7 +34,7 @@
  */
 class HalLinkDiscovererUnitTest extends LinkDiscovererUnitTest {
 
-	LinkDiscoverer discoverer = new HalLinkDiscoverer();
+	HalLinkDiscoverer discoverer = new HalLinkDiscoverer();
 	ContextualMapper $ = MappingTestUtils.createMapper();
 
 	/**
@@ -69,11 +68,24 @@ void discoversAllTheLinkAttributes() throws IOException {
 
 			assertThat(getDiscoverer().findLinkWithRel(IanaLinkRelations.SELF, linkText)).hasValue(expected);
 		});
+	}
+
+	@Test // GH-2385
+	void detectsEmbeddedLinks() {
+
+		var discoverer = getDiscoverer().inspectEmbeddeds();
 
+		$.assertFileContent("hal-link-discoverer.json").satisfies(it -> {
+
+			assertThat(discoverer.findLinksWithRel("relation", it))
+					.hasSize(3)
+					.extracting(Link::getHref)
+					.containsExactlyInAnyOrder("firstHref", "secondHref", "thirdHref");
+		});
 	}
 
 	@Override
-	protected LinkDiscoverer getDiscoverer() {
+	protected HalLinkDiscoverer getDiscoverer() {
 		return discoverer;
 	}
 

src/test/resources/org/springframework/hateoas/mediatype/hal/hal-link-discoverer.json

@@ -14,5 +14,14 @@
     "http://www.foo.com/bar": {
       "href": "fullRelHref"
     }
+  },
+  "_embedded": {
+    "relation": {
+      "_links": {
+        "relation" : {
+          "href": "thirdHref"
+        }
+      }
+    }
   }
-}
+}