From 1dea5f61b9eedf75ac09587b95969f19b56476a6 Mon Sep 17 00:00:00 2001
From: Oliver Drotbohm <ogierke@pivotal.io>
Date: Mon, 11 Feb 2019 10:41:25 +0100
Subject: [PATCH] =?UTF-8?q?#805=20-=20Added=20Links.getRequiredLink(?=
 =?UTF-8?q?=E2=80=A6).?=
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---
 .../org/springframework/hateoas/Links.java    | 13 +++++++++++++
 .../hateoas/LinksUnitTest.java                | 19 +++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/src/main/java/org/springframework/hateoas/Links.java b/src/main/java/org/springframework/hateoas/Links.java
index a8afb751..ec957f43 100644
--- a/src/main/java/org/springframework/hateoas/Links.java
+++ b/src/main/java/org/springframework/hateoas/Links.java
@@ -71,6 +71,19 @@ public class Links implements Iterable<Link> {
 				.filter(link -> link.getRel().equals(rel)).findFirst();
 	}
 
+	/**
+	 * Returns the {@link Link} with the given relation.
+	 *
+	 * @param rel the relation type to lookup a link for.
+	 * @return
+	 * @throws IllegalArgumentException if no link with the given relation was present.
+	 * @since 1.0
+	 */
+	public Link getRequiredLink(String rel) {
+
+		return getLink(rel) //
+				.orElseThrow(() -> new IllegalArgumentException(String.format("Couldn't find link with rel '%s'!", rel)));
+	}
 	/**
 	 * Returns all {@link Links} with the given relation type.
 	 * 
diff --git a/src/test/java/org/springframework/hateoas/LinksUnitTest.java b/src/test/java/org/springframework/hateoas/LinksUnitTest.java
index 78c30bc2..66a8bb0e 100755
--- a/src/test/java/org/springframework/hateoas/LinksUnitTest.java
+++ b/src/test/java/org/springframework/hateoas/LinksUnitTest.java
@@ -102,4 +102,23 @@ public class LinksUnitTest {
 	public void parsesLinksWithWhitespace() {
 		assertThat(Links.valueOf(WITH_WHITESPACE)).isEqualTo(reference);
 	}
+
+	@Test // #805
+	public void returnsRequiredLink() {
+
+		Link reference = new Link("http://localhost", "someRel");
+		Links links = new Links(reference);
+
+		assertThat(links.getRequiredLink("someRel")).isEqualTo(reference);
+	}
+
+	@Test // #805
+	public void rejectsMissingLinkWithIllegalArgumentException() {
+
+		Links links = new Links();
+
+		assertThatExceptionOfType(IllegalArgumentException.class) //
+				.isThrownBy(() -> links.getRequiredLink("self")) //
+				.withMessageContaining("self");
+	}
 }