1 files changed, 91 insertions, 0 deletions
diff --git a/server/src/com/vaadin/data/ContainerHelpers.java b/server/src/com/vaadin/data/ContainerHelpers.java
new file mode 100644
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+++ b/server/src/com/vaadin/data/ContainerHelpers.java
@@ -0,0 +1,91 @@
+package com.vaadin.data;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import com.vaadin.data.Container.Indexed;
+
+/**
+ * Contains helper methods for containers that can be used to ease development
+ * of containers in Vaadin.
+ * 
+ * @since 7.0
+ */
+public class ContainerHelpers {
+
+    /**
+     * Get a range of item ids from the container using
+     * {@link Indexed#getIdByIndex(int)}. This is just a helper method to aid
+     * developers to quickly add the required functionality to a Container
+     * during development. This should not be used in a "finished product"
+     * unless fetching an id for an index is very inexpensive because a separate
+     * request will be performed for each index in the range.
+     * 
+     * @param startIndex
+     *            index of the first item id to get
+     * @param numberOfIds
+     *            the number of consecutive items whose ids should be returned
+     * @param container
+     *            the container from which the items should be fetched
+     * @return A list of item ids in the range specified
+     */
+    public static List<?> getItemIdsUsingGetIdByIndex(int startIndex,
+            int numberOfIds, Container.Indexed container) {
+
+        if (container == null) {
+            throw new IllegalArgumentException(
+                    "The given container cannot be null!");
+        }
+
+        if (startIndex < 0) {
+            throw new IndexOutOfBoundsException(
+                    "Start index cannot be negative! startIndex=" + startIndex);
+        }
+
+        if (startIndex > container.size()) {
+            throw new IndexOutOfBoundsException(
+                    "Start index exceeds container size! startIndex="
+                            + startIndex + " containerLastItemIndex="
+                            + (container.size() - 1));
+        }
+
+        if (numberOfIds < 1) {
+            if (numberOfIds == 0) {
+                return Collections.emptyList();
+            }
+
+            throw new IllegalArgumentException(
+                    "Cannot get negative amount of items! numberOfItems="
+                            + numberOfIds);
+        }
+
+        // not included in the range
+        int endIndex = startIndex + numberOfIds;
+
+        if (endIndex > container.size()) {
+            throw new RangeOutOfContainerBoundsException(
+                    "Cannot get all requested item ids from container. "
+                            + "Container size might have changed, recalculate numberOfIds "
+                            + "based on the actual container size!",
+                    startIndex, numberOfIds, container.size());
+        }
+
+        ArrayList<Object> rangeOfIds = new ArrayList<Object>();
+        for (int i = startIndex; i < endIndex; i++) {
+            Object idByIndex = container.getIdByIndex(i);
+            if (idByIndex == null) {
+                throw new RuntimeException(
+                        "Unable to get item id for index: "
+                                + i
+                                + " from container using Container.Indexed#getIdByIndex() "
+                                + "even though container.size() > endIndex. "
+                                + "Returned item id was null. "
+                                + "Check your container implementation!");
+            }
+            rangeOfIds.add(idByIndex);
+        }
+
+        return Collections.unmodifiableList(rangeOfIds);
+    }
+}