How to convert column values from string to decimal?

I'm having a dataframe which contains a really big integer value, example:

42306810747081022358

When I've tried to convert it to long it was working in the Java but not under the spark envrironment, I was getting

   NumberFormatException: For input string("42306810747081022358")

Then I tried to convert it too Decimal (BigDecimal) value. Again, easily can do it in Java, but in Spark: dframe.withColumn("c_number",col("c_a").cast(new DecimalType()));

This way I don't get any exceptions, however I can see that all result values are null.

I also tried to use UDF for this purpose but get the same results:

UDF1 cTransformer = new UDF1<String, BigDecimal>() {        @Override        public BigDecimal call(String aString) throws Exception {            return new BigDecimal(aString);        }    };sqlContext.udf().register("cTransformer", cTransformer, new DecimalType());dframe = dframe.withColumn("c_number", callUDF("cTransformer", dframe.col("c_a"))); 

And here again all I'm getting is a column with all zeroes.

How should I proceed?