How to explode array columns of a dataframe having the same length

[sam smith]

Hello guys,

I have the following dataframe:

*col1*

*col2*

*col3*

["A","B","null"]

["C","D","null"]

["E","null","null"]
I want to explode it to the following dataframe:

*col1*

*col2*

*col3*

"A"

"C"

"E"

"B"

"D"

"null"

"null"

"null"

"null"

How to do that (preferably in Java) using the explode() method ? knowing
that something like the following won't yield correct output:

for (String colName: dataset.columns())
    dataset=dataset.withColumn(colName,explode(dataset.col(colName)));