Refactor connectivity intent creation to use builders

- Each connectivity intent now has only one constructor
- Intent constructors are now private for leaf classes and
  protected for classes that can be derived from
- Each intent class has a Builder class that accumulates
  parameters for intent creation
- Each intent class has a public static builder() method
  to create a builder
- Each Builder class has a build() method to create the
  intent from the accumulated parameters
- Added keys to a few intent types that were missing them
- Tightened up usage of checkNotNull(), taking advantage of
  the return value to save some lines of code
- Modified callers to use the builders instead of directly
  calling the constructors

Change-Id: I713185d5ecbadbf51f87ef7f68fec41102106c78
diff --git a/core/api/src/main/java/org/onosproject/net/intent/MultiPointToSinglePointIntent.java b/core/api/src/main/java/org/onosproject/net/intent/MultiPointToSinglePointIntent.java
index 721ff17..c92898e 100644
--- a/core/api/src/main/java/org/onosproject/net/intent/MultiPointToSinglePointIntent.java
+++ b/core/api/src/main/java/org/onosproject/net/intent/MultiPointToSinglePointIntent.java
@@ -16,6 +16,7 @@
 package org.onosproject.net.intent;
 
 import com.google.common.base.MoreObjects;
+import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Sets;
 import org.onosproject.core.ApplicationId;
 import org.onosproject.net.ConnectPoint;
@@ -42,29 +43,6 @@
      * traffic selector and treatment.
      *
      * @param appId         application identifier
-     * @param selector      traffic selector
-     * @param treatment     treatment
-     * @param ingressPoints set of ports from which ingress traffic originates
-     * @param egressPoint   port to which traffic will egress
-     * @throws NullPointerException     if {@code ingressPoints} or
-     *                                  {@code egressPoint} is null.
-     * @throws IllegalArgumentException if the size of {@code ingressPoints} is
-     *                                  not more than 1
-     */
-    public MultiPointToSinglePointIntent(ApplicationId appId,
-                                         TrafficSelector selector,
-                                         TrafficTreatment treatment,
-                                         Set<ConnectPoint> ingressPoints,
-                                         ConnectPoint egressPoint) {
-        this(appId, selector, treatment, ingressPoints, egressPoint,
-                Collections.emptyList(), DEFAULT_INTENT_PRIORITY);
-    }
-
-    /**
-     * Creates a new multi-to-single point connectivity intent for the specified
-     * traffic selector and treatment.
-     *
-     * @param appId         application identifier
      * @param key           intent key
      * @param selector      traffic selector
      * @param treatment     treatment
@@ -77,7 +55,7 @@
      * @throws IllegalArgumentException if the size of {@code ingressPoints} is
      *                                  not more than 1
      */
-    public MultiPointToSinglePointIntent(ApplicationId appId,
+    private MultiPointToSinglePointIntent(ApplicationId appId,
                                          Key key,
                                          TrafficSelector selector,
                                          TrafficTreatment treatment,
@@ -99,33 +77,6 @@
     }
 
     /**
-     * Creates a new multi-to-single point connectivity intent for the specified
-     * traffic selector and treatment.
-     *
-     * @param appId         application identifier
-     * @param selector      traffic selector
-     * @param treatment     treatment
-     * @param ingressPoints set of ports from which ingress traffic originates
-     * @param egressPoint   port to which traffic will egress
-     * @param constraints   constraints to apply to the intent
-     * @param priority      priority to use for flows generated by this intent
-     * @throws NullPointerException     if {@code ingressPoints} or
-     *                                  {@code egressPoint} is null.
-     * @throws IllegalArgumentException if the size of {@code ingressPoints} is
-     *                                  not more than 1
-     */
-    public MultiPointToSinglePointIntent(ApplicationId appId,
-                                         TrafficSelector selector,
-                                         TrafficTreatment treatment,
-                                         Set<ConnectPoint> ingressPoints,
-                                         ConnectPoint egressPoint,
-                                         List<Constraint> constraints,
-                                         int priority) {
-        this(appId, null, selector, treatment, ingressPoints, egressPoint,
-                constraints, priority);
-    }
-
-    /**
      * Constructor for serializer.
      */
     protected MultiPointToSinglePointIntent() {
@@ -135,6 +86,105 @@
     }
 
     /**
+     * Returns a new multi point to single point intent builder. The application id,
+     * ingress points and egress point are required fields.  If they are
+     * not set by calls to the appropriate methods, an exception will
+     * be thrown.
+     *
+     * @return single point to multi point builder
+     */
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    /**
+     * Builder of a multi point to single point intent.
+     */
+    public static final class Builder extends ConnectivityIntent.Builder {
+        Set<ConnectPoint> ingressPoints;
+        ConnectPoint egressPoint;
+
+        private Builder() {
+            // Hide constructor
+        }
+
+        @Override
+        public Builder appId(ApplicationId appId) {
+            return (Builder) super.appId(appId);
+        }
+
+        @Override
+        public Builder key(Key key) {
+            return (Builder) super.key(key);
+        }
+
+        @Override
+        public Builder selector(TrafficSelector selector) {
+            return (Builder) super.selector(selector);
+        }
+
+        @Override
+        public Builder treatment(TrafficTreatment treatment) {
+            return (Builder) super.treatment(treatment);
+        }
+
+        @Override
+        public Builder constraints(List<Constraint> constraints) {
+            return (Builder) super.constraints(constraints);
+        }
+
+        @Override
+        public Builder priority(int priority) {
+            return (Builder) super.priority(priority);
+        }
+
+        /**
+         * Sets the ingress point of the single point to multi point intent
+         * that will be built.
+         *
+         * @param ingressPoints ingress connect points
+         * @return this builder
+         */
+        public Builder ingressPoints(Set<ConnectPoint> ingressPoints) {
+            this.ingressPoints = ImmutableSet.copyOf(ingressPoints);
+            return this;
+        }
+
+        /**
+         * Sets the egress point of the multi point to single point intent
+         * that will be built.
+         *
+         * @param egressPoint egress connect point
+         * @return this builder
+         */
+        public Builder egressPoint(ConnectPoint egressPoint) {
+            this.egressPoint = egressPoint;
+            return this;
+        }
+
+        /**
+         * Builds a multi point to single point intent from the
+         * accumulated parameters.
+         *
+         * @return point to point intent
+         */
+        public MultiPointToSinglePointIntent build() {
+
+            return new MultiPointToSinglePointIntent(
+                    appId,
+                    key,
+                    selector,
+                    treatment,
+                    ingressPoints,
+                    egressPoint,
+                    constraints,
+                    priority
+            );
+        }
+    }
+
+
+    /**
      * Returns the set of ports on which ingress traffic should be connected to
      * the egress port.
      *