ARROW-886 [Java] Fixing reallocation of VariableLengthVector offsets

Author: Emilio Lahr-Vivaz <elahrvivaz@ccri.com>

Closes #591 from elahrvivaz/ARROW-886 and squashes the following commits:

5f6b4be [Emilio Lahr-Vivaz] ARROW-886 Fixing reallocation of VariableLengthVector offsets

java/vector/src/main/codegen/templates/VariableLengthVectors.java

@@ -355,6 +355,7 @@ public void reset() {
  }
 
  public void reAlloc() {
+ offsetVector.reAlloc();
  final long newAllocationSize = allocationSizeInBytes*2L;
  if (newAllocationSize > MAX_ALLOCATION_SIZE) {
  throw new OversizedAllocationException("Unable to expand the buffer. Max allowed buffer size is reached.");

java/vector/src/test/java/org/apache/arrow/vector/TestVectorReAlloc.java

@@ -72,6 +72,31 @@ public void testFixedType() {
  }
  }
 
+ @Test
+ public void testVariableLengthType() {
+ try (final VarCharVector vector = new VarCharVector("", allocator)) {
+ final VarCharVector.Mutator m = vector.getMutator();
+ // note: capacity ends up being - 1 due to offsets vector
+ vector.setInitialCapacity(511);
+ vector.allocateNew();
+
+ assertEquals(511, vector.getValueCapacity());
+
+ try {
+ m.set(512, "foo".getBytes(StandardCharsets.UTF_8));
+ Assert.fail("Expected out of bounds exception");
+ } catch (Exception e) {
+ // ok
+ }
+
+ vector.reAlloc();
+ assertEquals(1023, vector.getValueCapacity());
+
+ m.set(512, "foo".getBytes(StandardCharsets.UTF_8));
+ assertEquals("foo", new String(vector.getAccessor().get(512), StandardCharsets.UTF_8));
+ }
+ }
+
  @Test
  public void testNullableType() {
  try (final NullableVarCharVector vector = new NullableVarCharVector("", allocator)) {
@@ -89,7 +114,7 @@ public void testNullableType() {
  }
 
  vector.reAlloc();
- assertEquals(1023, vector.getValueCapacity()); // note: size - 1 for some reason...
+ assertEquals(1024, vector.getValueCapacity());
 
  m.set(512, "foo".getBytes(StandardCharsets.UTF_8));
  assertEquals("foo", new String(vector.getAccessor().get(512), StandardCharsets.UTF_8));