private void readFromJsonIntoVector()

in vector/src/main/java/org/apache/arrow/vector/ipc/JsonFileReader.java [850:950]
71 lines of code
16 McCabe index (conditional complexity)

  private void readFromJsonIntoVector(Field field, FieldVector vector) throws IOException {
    ArrowType type = field.getType();
    TypeLayout typeLayout = TypeLayout.getTypeLayout(type);
    List<BufferType> vectorTypes = typeLayout.getBufferTypes();
    List<ArrowBuf> vectorBuffers = new ArrayList<>(vectorTypes.size());
    List<Integer> variadicBufferIndices = new ArrayList<>();

    if (!typeLayout.isFixedBufferCount()) {
      vectorTypes.add(VARIADIC_DATA_BUFFERS);
    }
    /*
     * The order of inner buffers is:
     * Fixed width vector:
     *    -- validity buffer
     *    -- data buffer
     * Variable width vector:
     *    -- validity buffer
     *    -- offset buffer
     *    -- data buffer
     *
     * This is similar to what getFieldInnerVectors() used to give but now that we don't have
     * inner vectors anymore, we will work directly at the buffer level -- populate buffers
     * locally as we read from Json parser and do loadFieldBuffers on the vector followed by
     * releasing the local buffers.
     */
    readToken(START_OBJECT);
    {
      // If currently reading dictionaries, field name is not important so don't check
      String name = readNextField("name", String.class);
      if (started && !Objects.equals(field.getName(), name)) {
        throw new IllegalArgumentException(
            "Expected field " + field.getName() + " but got " + name);
      }

      /* Initialize the vector with required capacity but don't allocateNew since we would
       * be doing loadFieldBuffers.
       */
      int valueCount = readNextField("count", Integer.class);

      vector.setInitialCapacity(valueCount);

      for (int v = 0; v < vectorTypes.size(); v++) {
        BufferType bufferType = vectorTypes.get(v);
        nextFieldIs(bufferType.getName());
        int innerBufferValueCount = valueCount;
        if (bufferType.equals(OFFSET)
            && !(type instanceof Union)
            && !(type instanceof ListView)
            && !(type instanceof LargeListView)) {
          /* offset buffer has 1 additional value capacity except for dense unions and ListView */
          innerBufferValueCount = valueCount + 1;
        }

        vectorBuffers.addAll(
            readIntoBuffer(
                allocator,
                bufferType,
                vector.getMinorType(),
                innerBufferValueCount,
                variadicBufferIndices));
      }

      int nullCount;
      if (type instanceof ArrowType.RunEndEncoded || type instanceof Union) {
        nullCount = 0;
      } else if (type instanceof ArrowType.Null) {
        nullCount = valueCount;
      } else {
        nullCount = BitVectorHelper.getNullCount(vectorBuffers.get(0), valueCount);
      }
      final ArrowFieldNode fieldNode = new ArrowFieldNode(valueCount, nullCount);
      vector.loadFieldBuffers(fieldNode, vectorBuffers);

      /* read child vectors (if any) */
      List<Field> fields = field.getChildren();
      if (!fields.isEmpty()) {
        List<FieldVector> vectorChildren = vector.getChildrenFromFields();
        if (fields.size() != vectorChildren.size()) {
          throw new IllegalArgumentException(
              "fields and children are not the same size: "
                  + fields.size()
                  + " != "
                  + vectorChildren.size());
        }
        nextFieldIs("children");
        readToken(START_ARRAY);
        for (int i = 0; i < fields.size(); i++) {
          Field childField = fields.get(i);
          FieldVector childVector = vectorChildren.get(i);
          readFromJsonIntoVector(childField, childVector);
        }
        readToken(END_ARRAY);
      }
    }

    readToken(END_OBJECT);

    for (ArrowBuf buffer : vectorBuffers) {
      buffer.getReferenceManager().release();
    }
  }