parquet-hadoop/src/main/java/org/apache/parquet/hadoop/api/InitContext.java
@Deprecated
  public Map<String, String> getMergedKeyValueMetaData() {
    if (mergedKeyValueMetadata == null) {
      Map<String, String> mergedKeyValues = new HashMap<String, String>();
      for (Entry<String, Set<String>> entry : keyValueMetadata.entrySet()) {
        if (entry.getValue().size() > 1) {
          throw new RuntimeException("could not merge metadata: key " + entry.getKey() + " has conflicting values: " + entry.getValue());
        }
        mergedKeyValues.put(entry.getKey(), entry.getValue().iterator().next());
      }
      mergedKeyValueMetadata = mergedKeyValues;
    }
    return mergedKeyValueMetadata;
  }
@Deprecated
  public Map<String, String> getMergedKeyValueMetaData() {
    if (mergedKeyValueMetadata == null) {
      Map<String, String> mergedKeyValues = new HashMap<String, String>();
      for (Entry<String, Set<String>> entry : keyValueMetadata.entrySet()) {
        if (entry.getValue().size() > 1) {
          throw new RuntimeException("could not merge metadata: key " + entry.getKey() + " has conflicting values: " + entry.getValue());
        }
        mergedKeyValues.put(entry.getKey(), entry.getValue().iterator().next());
      }
      mergedKeyValueMetadata = mergedKeyValues;
    }
    return mergedKeyValueMetadata;
  }
If there is a conflicting value when reading from multiple files,
an exception will be thrown
@return the merged key values metadata form the file footers