Context.scala

package me.invkrh.spark

import org.apache.spark.sql.SQLContext
import org.apache.spark.{SparkContext, SparkConf}

object Context {
  val conf: SparkConf    = new SparkConf().setMaster("local[*]").setAppName("Test")
  val ctx : SparkContext = new SparkContext(conf)
  val sqlc: SQLContext   = new SQLContext(ctx)

  import sqlc.implicits._

  val df = Seq(("""hello\nworld""", 2), ("""hello\nworld""", 3), ("""hello\nworld""", 4)).toDF("a", "b")
}

replace.java

package me.invkrh.spark;

import org.apache.spark.sql.DataFrame;
import org.apache.spark.sql.types.DataTypes;
import static org.apache.spark.sql.functions.*;

public class StringTest {

  public static void main(String[] args) {

    DataFrame df = Context.df();
    df.withColumn("rep", regexp_replace(df.col("a"), "\\\\n", "\n")).show();

    Context.sqlc().udf().register("replaceWithLineFeed", (String text, String regexp, String replacement) -> {
      if (text == null) { return 0; }
      return text.replaceAll(regexp, replacement);
    }, DataTypes.StringType);
    Context.df().withColumn("rep", expr("replaceWithLineFeed(a,'\\\\n', '\n')")).show();

    System.out.println("hello\\nworld".replaceAll("\\\\n", "\n"));
  }
}