Avoid redundant autoboxing in BackEndDataProvider's size callback (#8127)

server/src/main/java/com/vaadin/data/provider/BackEndDataProvider.java

@@ -21,6 +21,7 @@ import java.util.Objects;
 import java.util.stream.Stream;
 
 import com.vaadin.server.SerializableFunction;
+import com.vaadin.server.SerializableToIntFunction;
 import com.vaadin.shared.Registration;
 
 /**
@@ -34,7 +35,7 @@ import com.vaadin.shared.Registration;
 public class BackEndDataProvider<T, F> extends AbstractDataProvider<T, F> {
 
     private final SerializableFunction<Query<T, F>, Stream<T>> request;
-    private final SerializableFunction<Query<T, F>, Integer> sizeCallback;
+    private final SerializableToIntFunction<Query<T, F>> sizeCallback;
 
     /**
      * Constructs a new DataProvider to request data from an arbitrary back end
@@ -47,7 +48,7 @@ public class BackEndDataProvider<T, F> extends AbstractDataProvider<T, F> {
      */
     public BackEndDataProvider(
             SerializableFunction<Query<T, F>, Stream<T>> request,
-            SerializableFunction<Query<T, F>, Integer> sizeCallback) {
+            SerializableToIntFunction<Query<T, F>> sizeCallback) {
         Objects.requireNonNull(request, "Request function can't be null");
         Objects.requireNonNull(sizeCallback, "Size callback can't be null");
         this.request = request;
@@ -61,7 +62,7 @@ public class BackEndDataProvider<T, F> extends AbstractDataProvider<T, F> {
 
     @Override
     public int size(Query<T, F> query) {
-        return sizeCallback.apply(query);
+        return sizeCallback.applyAsInt(query);
     }
 
     /**

server/src/main/java/com/vaadin/server/SerializableToIntFunction.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2000-2016 Vaadin Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.vaadin.server;
+
+import java.io.Serializable;
+import java.util.function.ToIntFunction;
+
+/**
+ * A {@link ToIntFunction} that is also {@link Serializable}.
+ * 
+ * @see ToIntFunction
+ * @author Vaadin Ltd
+ * @since 8.0
+ * 
+ * @param <T>
+ *            the type of the input for this function
+ */
+@FunctionalInterface
+public interface SerializableToIntFunction<T>
+        extends ToIntFunction<T>, Serializable {
+
+}