GH-44332: [Java] Implement VectorAppender for BaseVariableWidthViewVector

java/vector/src/main/java/org/apache/arrow/vector/util/VectorAppender.java

@@ -19,6 +19,8 @@
 import static org.apache.arrow.memory.util.LargeMemoryUtil.checkedCastToInt;
 
 import java.util.HashSet;
+import java.util.List;
+import org.apache.arrow.memory.ArrowBuf;
 import org.apache.arrow.memory.util.MemoryUtil;
 import org.apache.arrow.util.Preconditions;
 import org.apache.arrow.vector.BaseFixedWidthVector;
@@ -247,8 +249,63 @@ public ValueVector visit(BaseLargeVariableWidthVector deltaVector, Void value) {
   }
 
   @Override
-  public ValueVector visit(BaseVariableWidthViewVector left, Void value) {
-    throw new UnsupportedOperationException("View vectors are not supported.");
+  public ValueVector visit(BaseVariableWidthViewVector deltaVector, Void value) {
+    Preconditions.checkArgument(
+        typeVisitor.equals(deltaVector),
+        "The targetVector to append must have the same type as the targetVector being appended");
+
+    if (deltaVector.getValueCount() == 0) {
+      return targetVector; // nothing to append, return
+    }
+
+    int oldTargetValueCount = targetVector.getValueCount();
+    int newValueCount = oldTargetValueCount + deltaVector.getValueCount();
+
+    // make sure there is enough capacity
+    while (targetVector.getValueCapacity() < newValueCount) {
+      targetVector.reAlloc();
+    }
+
+    // append validity buffer
+    BitVectorHelper.concatBits(
+        targetVector.getValidityBuffer(),
+        oldTargetValueCount,
+        deltaVector.getValidityBuffer(),
+        deltaVector.getValueCount(),
+        targetVector.getValidityBuffer());
+
+    // append data buffers
+    BaseVariableWidthViewVector targetViewVector = (BaseVariableWidthViewVector) targetVector;
+    List<ArrowBuf> targetDataBuffers = targetViewVector.getDataBuffers();
+    final int oldTargetDataBufferCount = targetDataBuffers.size();
+    List<ArrowBuf> deltaVectorDataBuffers = deltaVector.getDataBuffers();
+    deltaVectorDataBuffers.forEach(buf -> buf.getReferenceManager().retain());
+    targetDataBuffers.addAll(deltaVectorDataBuffers);
+
+    // append view buffer
+    ArrowBuf targetViewBuffer = targetVector.getDataBuffer();
+    MemoryUtil.copyMemory(
+        deltaVector.getDataBuffer().memoryAddress(),
+        targetViewBuffer.memoryAddress()
+            + (long) BaseVariableWidthViewVector.ELEMENT_SIZE * oldTargetValueCount,
+        (long) BaseVariableWidthViewVector.ELEMENT_SIZE * deltaVector.getValueCount());
+
+    // update view buffer
+    for (int i = oldTargetValueCount; i < newValueCount; i++) {
+      if (targetViewVector.isSet(i) > 0
+          && targetViewVector.getValueLength(i) > BaseVariableWidthViewVector.INLINE_SIZE) {
+        long start =
+            (long) i * BaseVariableWidthViewVector.ELEMENT_SIZE
+                + BaseVariableWidthViewVector.LENGTH_WIDTH
+                + BaseVariableWidthViewVector.PREFIX_WIDTH;
+        // shift buf id
+        int bufferId = targetViewBuffer.getInt(start);
+        targetViewBuffer.setInt(start, bufferId + oldTargetDataBufferCount);
+      }
+    }
+
+    targetVector.setValueCount(newValueCount);
+    return targetVector;
   }
 
   @Override

java/vector/src/test/java/org/apache/arrow/vector/util/TestVectorAppender.java

@@ -34,6 +34,7 @@
 import org.apache.arrow.vector.LargeVarCharVector;
 import org.apache.arrow.vector.ValueVector;
 import org.apache.arrow.vector.VarCharVector;
+import org.apache.arrow.vector.ViewVarCharVector;
 import org.apache.arrow.vector.compare.Range;
 import org.apache.arrow.vector.compare.RangeEqualsVisitor;
 import org.apache.arrow.vector.compare.TypeEqualsVisitor;
@@ -171,6 +172,32 @@ public void testAppendVariableWidthVector() {
     }
   }
 
+  @Test
+  public void testAppendVariableWidthViewVector() {
+    final int length1 = 10;
+    final int length2 = 5;
+    try (ViewVarCharVector target = new ViewVarCharVector("", allocator);
+        ViewVarCharVector delta = new ViewVarCharVector("", allocator)) {
+
+      target.setValueCount(length1);
+      delta.setValueCount(length2);
+
+      for (int i = 0; i < length1; i++) {
+        target.setSafe(i, (i + "xxxxxxxxxxxx").getBytes());
+      }
+
+      for (int i = 0; i < length2; i++) {
+        delta.setSafe(i, (i + "xxxxxxxxxxxx").getBytes());
+      }
+
+      VectorAppender appender = new VectorAppender(target);
+      delta.accept(appender, null);
+
+      assertEquals(15, target.getValueCount());
+      target.accept(new RangeEqualsVisitor(target, delta), new Range(10, 0, 5));
+    }
+  }
+
   @Test
   public void testAppendEmptyVariableWidthVector() {
     try (VarCharVector target = new VarCharVector("", allocator);