Add getKey(String keyId) to KeysApi (#1180)

Fixes #1176

Author: LeJeanbono

src/main/java/org/gitlab4j/api/KeysApi.java

@@ -10,7 +10,7 @@
 
 /**
  * See:
- * https://docs.gitlab.com/ee/api/keys.html#get-user-by-fingerprint-of-ssh-key
+ * <a href="https://docs.gitlab.com/ee/api/keys.html">GitLab Key API Documentaion</a>
  */
 public class KeysApi extends AbstractApi {
     public KeysApi(GitLabApi gitLabApi) {
@@ -28,4 +28,18 @@ public Key getUserBySSHKeyFingerprint(String fingerprint) throws GitLabApiExcept
         Response response = get(Response.Status.OK, queryParams, "keys");
         return response.readEntity(Key.class);
     }
+
+    /**
+     * Get a single key by id.
+     *
+     * <pre><code>GitLab Endpoint: GET /keys/:id</code></pre>
+     *
+     * @param keyId the IID of the key to get
+     * @return a Key instance
+     * @throws GitLabApiException if any exception occurs
+     */
+    public Key getKey(String keyId) throws GitLabApiException {
+        Response response = get(Response.Status.OK, null, "keys", keyId);
+        return response.readEntity(Key.class);
+    }
 }