How to form a list of maps in java spark

Question

root
 |-- code: string (nullable = true)
 |-- mnemonic: string (nullable = true)
 |-- key: long (nullable = true)
 |-- country: string (nullable = true)
 |-- crossID: struct (nullable = false)
 |    |-- codeKey: long (nullable = true)
 |    |-- codeGroupCode: string (nullable = true)
 |    |-- description: string (nullable = true)
 |    |-- externalCode: string (nullable = true)
 |-- ITEM: struct (nullable = false)
 |    |-- type: string (nullable = true)
 |    |-- indicator: string (nullable = true)
 |    |-- imageIndicator: string (nullable = true)
 |    |-- col20: struct (nullable = false)
 |    |    |-- cCode: string (nullable = true)
 |    |    |-- vCode: string (nullable = true)

The above is the schema of my dataframe. Here I would like group the crossID and its elements as list of maps. Please help me how to do it in java spark.