public List<HCatFieldSchema> getFields() {
    return Collections.unmodifiableList(this.fieldSchemas);
  }
Users are not allowed to modify the list directly, since HCatSchema
 maintains internal state. Use append/remove to modify the schema.
hcatalog/core/src/main/java/org/apache/hive/hcatalog/data/schema/HCatSchema.java