[Java] MapVector written data does not meet expectations

使用 MapVector 和 UnionMapWriter 重现提供的 Java 代码片段，然后检查 MapVector 和 UnionMapWriter 的写入路径，了解其对不同键类型和值类型的处理。比较现有的 ListVector 文档示例，并将完成定义为以下任一项：成功写入具有混合类型的 MapVector，或提供一个有文档说明且可运行的 MapVector 示例，并由回归测试支持。

What would you like help with?

    RootAllocator allocator = new RootAllocator(Long.MAX_VALUE);
    Map<String, String> metadata = new HashMap<>();
    metadata.put("K1", "V1");
    metadata.put("K2", "V2");
    Field a = new Field("key", FieldType.notNullable(new ArrowType.Int(32, true)), null);
    Field b = new Field("value", FieldType.nullable(new ArrowType.Int(32,true)), null);
    Schema schema = new Schema(asList(a, b), metadata);
    Field struct = new Field("struct", FieldType.notNullable(new ArrowType.Struct()), schema.getFields());
    StructVector structVector = new StructVector(Field.nullable("struct", struct.getType()), allocator, null);
    MapVector mapVector = new MapVector(Field.nullable("map", structVector.getField().getType()), allocator, null);
    mapVector.initializeChildrenFromFields(Collections.singletonList(struct));
    mapVector.allocateNew();
    
    UnionMapWriter writer = mapVector.getWriter();
    for (int i = 0; i < 10; i++) {
        writer.startMap();
        writer.setPosition(i);
        writer.key().writeInt(i);
        writer.value().writeInt(i * 10);
        writer.endMap();
    }
    writer.setValueCount(10);

when the types of key and value are different, data cannot be written .
Only examples of ListVector are available in the documentation on the official website ,Please provide an example of writing data to MapVector.