Added support to list MergeRequests by state (#110)

* Added support to list MergeRequests by state
* Added getMergeRequests by State with paging support

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

@@ -169,6 +169,28 @@ public interface Constants {
         }
     }
 
+    /** Enum to use for querying the state of a MergeRequest */
+    public enum MergeRequestState {
+        OPENED, CLOSED, MERGED, ALL;
+
+        private static JacksonJsonEnumHelper<MergeRequestState> enumHelper = new JacksonJsonEnumHelper<>(MergeRequestState.class);
+
+        @JsonCreator
+        public static MergeRequestState forValue(String value) { return enumHelper.forValue(value); }
+
+
+        @JsonValue
+        public String toValue() {
+            return (enumHelper.toString(this));
+        }
+
+        @Override
+        public String toString() {
+            return (enumHelper.toString(this));
+        }
+    }
+
+
     /** Enum to use for specifying the state of a merge request or issue update. */
     public enum StateEvent {
 

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

@@ -63,6 +63,63 @@ public class MergeRequestApi extends AbstractApi {
         return (new Pager<MergeRequest>(this, MergeRequest.class, itemsPerPage, null, "projects", projectId, "merge_requests"));
     }
 
+    /**
+     * Get all merge requests for the specified project.
+     *
+     * GET /projects/:id/merge_requests
+     *
+     * @param projectId the project ID to get the merge requests for
+     * @param page the page to get
+     * @param perPage the number of MergeRequest instances per page
+     * @param state the state parameter can be used to get only merge requests with a given state (opened, closed, or merged) or all of them (all).
+     * @return all merge requests for the specified project
+     * @throws GitLabApiException if any exception occurs
+     */
+    public List<MergeRequest> getMergeRequests(Integer projectId, int page, int perPage, MergeRequestState state) throws GitLabApiException {
+        Form formData = new GitLabApiForm()
+                .withParam("state", state)
+                .withParam(PAGE_PARAM, page)
+                .withParam(PER_PAGE_PARAM, perPage);
+        Response response = get(Response.Status.OK, formData.asMap(), "projects", projectId, "merge_requests");
+        return (response.readEntity(new GenericType<List<MergeRequest>>() {}));
+    }
+
+
+    /**
+     * Get all merge requests for the specified project.
+     *
+     * GET /projects/:id/merge_requests
+     *
+     * @param projectId the project ID to get the merge requests for
+     * @param itemsPerPage the number of MergeRequest instances that will be fetched per page
+     * @param state the state parameter can be used to get only merge requests with a given state (opened, closed, or merged) or all of them (all).
+     * @return all merge requests for the specified project
+     * @throws GitLabApiException if any exception occurs
+     */
+    public Pager<MergeRequest> getMergeRequests(Integer projectId, int itemsPerPage, MergeRequestState state) throws GitLabApiException {
+        Form formData = new GitLabApiForm()
+                .withParam("state", state);
+        return (new Pager<MergeRequest>(this, MergeRequest.class, itemsPerPage, formData.asMap(), "projects", projectId, "merge_requests"));
+    }
+
+    /**
+     * Get all merge requests with a specific state for the specified project.
+     *
+     * GET /projects/:id/merge_requests?state=:state
+     *
+     * @param projectId the project ID to get the merge requests for
+     * @param state the state parameter can be used to get only merge requests with a given state (opened, closed, or merged) or all of them (all).
+     * @return all merge requests for the specified project
+     * @throws GitLabApiException if any exception occurs
+     */
+    public List<MergeRequest> getMergeRequests(Integer projectId, MergeRequestState state) throws GitLabApiException {
+        Form formData = new GitLabApiForm()
+                .withParam("state", state)
+                .withParam(PER_PAGE_PARAM, getDefaultPerPage());
+        Response response = get(Response.Status.OK, formData.asMap(), "projects", projectId, "merge_requests");
+        return (response.readEntity(new GenericType<List<MergeRequest>>() {}));
+    }
+
     /**
      * Get information about a single merge request.
      *