Added createPipeline() method that takes the variables param (#321).

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

@@ -2,6 +2,8 @@ package org.gitlab4j.api;
 
 import java.util.Date;
 import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
 
 import javax.ws.rs.core.Form;
 import javax.ws.rs.core.MultivaluedHashMap;
@@ -134,6 +136,36 @@ public class GitLabApiForm extends Form {
         return (this);
     }
 
+    /**
+     * Fluent method for adding an array of hash type query and form parameters to a get() or post() call.
+     *
+     * @param name the name of the field/attribute to add
+     * @param variables a Map containing array of hashes
+     * @param required the field is required flag
+     * @return this GitLabAPiForm instance
+     * @throws IllegalArgumentException if a required parameter is null or empty
+     */
+    public GitLabApiForm withParam(String name, Map<String, ?> variables, boolean required) throws IllegalArgumentException {
+
+        if (variables == null || variables.isEmpty()) {
+            if (required) {
+                throw new IllegalArgumentException(name + " cannot be empty or null");
+            }
+
+            return (this);
+        }
+
+        for (Entry<String, ?> variable : variables.entrySet()) {
+            Object value = variable.getValue();
+            if (value != null) {
+                this.param(name + "[][key]", variable.getKey());
+                this.param(name + "[][value]", value.toString());
+            }
+        }
+
+        return (this);
+    }
+
     /**
      * Fluent method for adding query and form parameters to a get() or post() call.
      * If required is true and value is null, will throw an IllegalArgumentException.

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

 package org.gitlab4j.api;
 
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 import java.util.stream.Stream;
 
@@ -224,7 +225,25 @@ public class PipelineApi extends AbstractApi implements Constants {
      * @throws GitLabApiException if any exception occurs during execution
      */
     public Pipeline createPipeline(Object projectIdOrPath, String ref) throws GitLabApiException {
-        GitLabApiForm formData = new GitLabApiForm().withParam("ref", ref);
+        return (createPipeline(projectIdOrPath, ref, null));
+    }
+
+    /**
+     * Create a pipelines in a project.
+     *
+     * <pre><code>GitLab Endpoint: POST /projects/:id/pipeline</code></pre>
+     *
+     * @param projectIdOrPath the project in the form of an Integer(ID), String(path), or Project instance
+     * @param ref reference to commit
+     * @param variables a Map containing the variables available in the pipeline
+     * @return a Pipeline instance with the newly created pipeline info
+     * @throws GitLabApiException if any exception occurs during execution
+     */
+    public Pipeline createPipeline(Object projectIdOrPath, String ref, Map<String, String> variables) throws GitLabApiException {
+
+        GitLabApiForm formData = new GitLabApiForm()
+                .withParam("ref", ref, true)
+                .withParam("variables", variables, false);
         Response response = post(Response.Status.CREATED, formData.asMap(), "projects", getProjectIdOrPath(projectIdOrPath), "pipeline");
         return (response.readEntity(Pipeline.class));
     }