Use list view accessors in union readers

Author: bodduv

vector/src/main/java/org/apache/arrow/vector/complex/LargeListViewVector.java

@@ -960,4 +960,18 @@ public void validate() {
   public void endValue(int index, int size) {
     sizeBuffer.setInt((long) index * SIZE_WIDTH, size);
   }
+
+  /** Get data vector start index with the given list index. */
+  public int getElementStartIndex(int index) {
+    return offsetBuffer.getInt((long) index * OFFSET_WIDTH);
+  }
+
+  private int getElementSize(int index) {
+    return sizeBuffer.getInt((long) index * SIZE_WIDTH);
+  }
+
+  /** Get data vector end index with the given list index. */
+  public int getElementEndIndex(int index) {
+    return getElementStartIndex(index) + getElementSize(index);
+  }
 }

vector/src/main/java/org/apache/arrow/vector/complex/impl/UnionLargeListViewReader.java

@@ -19,7 +19,6 @@
 import static org.apache.arrow.memory.util.LargeMemoryUtil.checkedCastToInt;
 
 import org.apache.arrow.vector.ValueVector;
-import org.apache.arrow.vector.complex.BaseLargeRepeatedValueViewVector;
 import org.apache.arrow.vector.complex.LargeListViewVector;
 import org.apache.arrow.vector.complex.reader.FieldReader;
 import org.apache.arrow.vector.holders.UnionHolder;
@@ -67,16 +66,12 @@ public void setPosition(int index) {
         vector.getOffsetBuffer(),
         vector.getSizeBuffer(),
         index,
-        BaseLargeRepeatedValueViewVector.OFFSET_WIDTH,
-        BaseLargeRepeatedValueViewVector.SIZE_WIDTH);
+        LargeListViewVector.OFFSET_WIDTH,
+        LargeListViewVector.SIZE_WIDTH);
 
     super.setPosition(index);
-    currentOffset =
-        vector
-            .getOffsetBuffer()
-            .getInt(index * (long) BaseLargeRepeatedValueViewVector.OFFSET_WIDTH);
-    size =
-        vector.getSizeBuffer().getInt(index * (long) BaseLargeRepeatedValueViewVector.SIZE_WIDTH);
+    currentOffset = vector.getElementStartIndex(index);
+    size = vector.getElementEndIndex(index) - currentOffset;
   }
 
   private void setEmptyPosition(int index) {

vector/src/main/java/org/apache/arrow/vector/complex/impl/UnionListViewReader.java

@@ -17,7 +17,6 @@
 package org.apache.arrow.vector.complex.impl;
 
 import org.apache.arrow.vector.ValueVector;
-import org.apache.arrow.vector.complex.BaseRepeatedValueViewVector;
 import org.apache.arrow.vector.complex.ListViewVector;
 import org.apache.arrow.vector.complex.reader.FieldReader;
 import org.apache.arrow.vector.holders.UnionHolder;
@@ -65,13 +64,12 @@ public void setPosition(int index) {
         vector.getOffsetBuffer(),
         vector.getSizeBuffer(),
         index,
-        BaseRepeatedValueViewVector.OFFSET_WIDTH,
-        BaseRepeatedValueViewVector.SIZE_WIDTH);
+        ListViewVector.OFFSET_WIDTH,
+        ListViewVector.SIZE_WIDTH);
 
     super.setPosition(index);
-    currentOffset =
-        vector.getOffsetBuffer().getInt(index * (long) BaseRepeatedValueViewVector.OFFSET_WIDTH);
-    size = vector.getSizeBuffer().getInt(index * (long) BaseRepeatedValueViewVector.SIZE_WIDTH);
+    currentOffset = vector.getElementStartIndex(index);
+    size = vector.getElementEndIndex(index) - currentOffset;
   }
 
   private void setEmptyPosition(int index) {