Now uses Constants enums instead of String literals.

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

 package org.gitlab4j.api;
 
-import java.util.HashMap;
 import java.util.List;
-import java.util.Map;
 
 import javax.ws.rs.core.GenericType;
 import javax.ws.rs.core.Response;
 
+import org.gitlab4j.api.GitLabApiConstants.PipelineOrderBy;
+import org.gitlab4j.api.GitLabApiConstants.PipelineScope;
+import org.gitlab4j.api.GitLabApiConstants.SortOrder;
 import org.gitlab4j.api.models.Pipeline;
 import org.gitlab4j.api.models.PipelineStatus;
 
-import com.fasterxml.jackson.annotation.JsonCreator;
-import com.fasterxml.jackson.annotation.JsonValue;
-
 /**
  * This class provides an entry point to all the GitLab API pipeline calls.
  */
-public class PipelineApi extends AbstractApi {
-
-    /** Enum to use for specifying the scope when calling getPipelines(). */
-    public enum Scope {
-
-        RUNNING, PENDING, FINISHED, BRANCHES, TAGS;
-
-        private static Map<String, Scope> valuesMap = new HashMap<>(5);
-        static {
-            for (Scope scope : Scope.values())
-                valuesMap.put(scope.toValue(), scope);
-        }
-
-        @JsonCreator
-        public static Scope forValue(String value) {
-            return valuesMap.get(value);
-        }
-
-        @JsonValue
-        public String toValue() {
-            return (name().toLowerCase());
-        }
-
-        @Override
-        public String toString() {
-            return (name().toLowerCase());
-        }
-    }
-
-    /** Enum to use for ordering the results of getPipelines(). */
-    public enum OrderBy {
-
-        ID, STATUS, REF, USER_ID;
-
-        private static Map<String, OrderBy> valuesMap = new HashMap<>(4);
-        static {
-            for (OrderBy orderBy : OrderBy.values())
-                valuesMap.put(orderBy.toValue(), orderBy);
-        }
-
-        @JsonCreator
-        public static OrderBy forValue(String value) {
-            return valuesMap.get(value);
-        }
-
-        @JsonValue
-        public String toValue() {
-            return (name().toLowerCase());
-        }
-
-        @Override
-        public String toString() {
-            return (name().toLowerCase());
-        }
-    }
+public class PipelineApi extends AbstractApi implements GitLabApiConstants {
 
     public PipelineApi(GitLabApi gitLabApi) {
         super(gitLabApi);
@@ -104,12 +48,12 @@ public class PipelineApi extends AbstractApi {
      * @param name the name of the user who triggered pipelines
      * @param username the username of the user who triggered pipelines
      * @param orderBy order pipelines by ID, STATUS, REF, USER_ID (default: ID)
-     * @param sort sort pipelines in "ASC" or "DESC" order (default: "DESC")
+     * @param sort sort pipelines in ASC or DESC order (default: DESC)
      * @return a list containing the pipelines for the specified project ID
      * @throws GitLabApiException if any exception occurs during execution
      */
-    public List<Pipeline> getPipelines(int projectId, Scope scope, PipelineStatus status, String ref, boolean yamlErrors, 
-            String name, String username, OrderBy orderBy, String sort) throws GitLabApiException {
+    public List<Pipeline> getPipelines(int projectId, PipelineScope scope, PipelineStatus status, String ref, boolean yamlErrors, 
+            String name, String username, PipelineOrderBy orderBy, SortOrder sort) throws GitLabApiException {
         GitLabApiForm formData = new GitLabApiForm()
                 .withParam("scope", scope)
                 .withParam("status", status)
@@ -118,7 +62,7 @@ public class PipelineApi extends AbstractApi {
                 .withParam("name", name)
                 .withParam("username", username)
                 .withParam("order_by", orderBy)
-                .withParam("sort", (sort != null ? sort.toLowerCase() : null));
+                .withParam("sort", sort);
 
         Response response = get(Response.Status.OK, formData.asMap(), "projects", projectId, "pipelines");
         return (response.readEntity(new GenericType<List<Pipeline>>() {

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

@@ -8,6 +8,8 @@ import javax.ws.rs.core.Form;
 import javax.ws.rs.core.GenericType;
 import javax.ws.rs.core.Response;
 
+import org.gitlab4j.api.GitLabApiConstants.ProjectOrderBy;
+import org.gitlab4j.api.GitLabApiConstants.SortOrder;
 import org.gitlab4j.api.GitLabApi.ApiVersion;
 import org.gitlab4j.api.models.Event;
 import org.gitlab4j.api.models.Issue;
@@ -58,6 +60,8 @@ public class ProjectApi extends AbstractApi {
      * @param statistics include project statistics
      * @return a list of projects accessible by the authenticated user and matching the supplied parameters
      * @throws GitLabApiException if any exception occurs
+     * @deprecated  Will be removed in version 5.0, replaced by {@link #getProjects(Boolean, Visibility, 
+     *      ProjectOrderBy, SortOrder, String, Boolean, Boolean, Boolean, Boolean, Boolean)}
      */
     public List<Project> getProjects(Boolean archived, Visibility visibility, String orderBy,
             String sort, String search, Boolean simple, Boolean owned, Boolean membership,
@@ -81,6 +85,48 @@ public class ProjectApi extends AbstractApi {
         }));
     }
 
+    /**
+     * Get a list of projects accessible by the authenticated user and matching the supplied filter parameters.
+     * All filter parameters are optional.
+     *
+     * GET /projects
+     *
+     * @param archived limit by archived status
+     * @param visibility limit by visibility public, internal, or private
+     * @param orderBy return projects ordered by ID, NAME, PATH, CREATED_AT, UPDATED_AT, or 
+     *          LAST_ACTIVITY_AT fields, default is CREATED_AT
+     * @param sort return projects sorted in asc or desc order. Default is desc
+     * @param search return list of projects matching the search criteria
+     * @param simple return only the ID, URL, name, and path of each project
+     * @param owned limit by projects owned by the current user
+     * @param membership limit by projects that the current user is a member of
+     * @param starred limit by projects starred by the current user
+     * @param statistics include project statistics
+     * @return a list of projects accessible by the authenticated user and matching the supplied parameters
+     * @throws GitLabApiException if any exception occurs
+     */
+    public List<Project> getProjects(Boolean archived, Visibility visibility, ProjectOrderBy orderBy,
+            SortOrder sort, String search, Boolean simple, Boolean owned, Boolean membership,
+            Boolean starred, Boolean statistics) throws GitLabApiException {
+
+        GitLabApiForm formData = new GitLabApiForm()
+                .withParam("archived", archived)
+                .withParam("visibility", visibility)
+                .withParam("order_by", orderBy)
+                .withParam("sort", sort)
+                .withParam("search", search)
+                .withParam("simple", simple)
+                .withParam("owned", owned)
+                .withParam("membership", membership)
+                .withParam("starred", starred)
+                .withParam("statistics", statistics)
+                .withParam("per_page", getDefaultPerPage());
+
+        Response response = get(Response.Status.OK, formData.asMap(), "projects");
+        return (response.readEntity(new GenericType<List<Project>>() {
+        }));
+    }
+
     /**
      * Get a list of projects accessible by the authenticated user that match the provided search string.
      *
@@ -160,7 +206,9 @@ public class ProjectApi extends AbstractApi {
      */
     public List<Project> getStarredProjects() throws GitLabApiException {
 
-        Form formData = new GitLabApiForm().withParam("starred", true).withParam("per_page", getDefaultPerPage());
+        Form formData = new GitLabApiForm()
+                .withParam("starred", true)
+                .withParam("per_page", getDefaultPerPage());
         Response response = get(Response.Status.OK, formData.asMap(), "projects");
         return (response.readEntity(new GenericType<List<Project>>() {
         }));