Add Column.getValueProvider to Grid (#8732)

* Add Column.getValueProvider to Grid

Fixes #8680

server/src/main/java/com/vaadin/ui/Grid.java

@@ -645,8 +645,8 @@ public class Grid<T> extends AbstractListing<T> implements HasComponents,
                         .hasKey(diffStateKey) : "Field name has changed";
                 Type type = null;
                 try {
-                    type = getState(false).getClass()
-                            .getField(diffStateKey).getGenericType();
+                    type = getState(false).getClass().getField(diffStateKey)
+                            .getGenericType();
                 } catch (NoSuchFieldException | SecurityException e) {
                     e.printStackTrace();
                 }
@@ -887,7 +887,8 @@ public class Grid<T> extends AbstractListing<T> implements HasComponents,
             if (hasCommonComparableBaseType(a, b)) {
                 return compareComparables(a, b);
             } else {
-                return compareComparables(Objects.toString(a, ""), Objects.toString(b, ""));
+                return compareComparables(Objects.toString(a, ""),
+                        Objects.toString(b, ""));
             }
         }
 
@@ -907,7 +908,7 @@ public class Grid<T> extends AbstractListing<T> implements HasComponents,
                 }
             }
             if ((a == null && b instanceof Comparable<?>)
-                || (b == null && a instanceof Comparable<?>)) {
+                    || (b == null && a instanceof Comparable<?>)) {
                 return true;
             }
 
@@ -1075,6 +1076,16 @@ public class Grid<T> extends AbstractListing<T> implements HasComponents,
             return this;
         }
 
+        /**
+         * Gets the function used to produce the value for data in this column
+         * based on the row item.
+         *
+         * @return the value provider function
+         */
+        public SerializableFunction<T, ? extends V> getValueProvider() {
+            return valueProvider;
+        }
+
         /**
          * Sets whether the user can sort this column or not.
          *

server/src/test/java/com/vaadin/tests/components/grid/GridValueProvider.java

@@ -0,0 +1,48 @@
+/*
+ * 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.tests.components.grid;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.vaadin.tests.data.bean.Person;
+import com.vaadin.tests.data.bean.Sex;
+import com.vaadin.ui.Grid;
+import com.vaadin.ui.Grid.Column;
+
+public class GridValueProvider {
+
+    @Test
+    public void getExplicitValueProvider() {
+        Grid<Person> grid = new Grid<>();
+        Column<Person, String> col = grid.addColumn(
+                person -> person.getFirstName() + " " + person.getLastName());
+        Person person = new Person("first", "last", "email", 123, Sex.UNKNOWN,
+                null);
+        Assert.assertEquals("first last", col.getValueProvider().apply(person));
+    }
+
+    @Test
+    public void getBeanColumnValueProvider() {
+        Grid<Person> grid = new Grid<>(Person.class);
+        Column<Person, String> col = (Column<Person, String>) grid
+                .getColumn("email");
+        Person person = new Person("first", "last", "eeemaaail", 123,
+                Sex.UNKNOWN, null);
+        Assert.assertEquals("eeemaaail", col.getValueProvider().apply(person));
+
+    }
+}