parquet-hadoop/src/main/java/org/apache/parquet/hadoop/api/ReadSupport.java
public ReadContext init(InitContext context) {
    return init(context.getConfiguration(), context.getMergedKeyValueMetaData(), context.getFileSchema());
  }
public ReadContext init(InitContext context) {
    return init(context.getConfiguration(), context.getMergedKeyValueMetaData(), context.getFileSchema());
  }
called in {@link org.apache.hadoop.mapreduce.InputFormat#getSplits(org.apache.hadoop.mapreduce.JobContext)} in the front end

@param context the initialisation context
@return the readContext that defines how to read the file