CH9.3 Reading and Writing json files

JSON file:   In Spark, when we refer to JSON files, we refer to line-delimited JSON files. This contrasts with files that have a large JSON object or array per file.   The line-delimited versus multiline trade-off is controlled by a single option: multiLine. When you set this option to true, you can read an entire file as one json object and Spark will go through the work of parsing that into a DataFrame.   Line-delimited JSON is actually a much more stable format because it allows you to append to a file with a new record (rather than having to read in an entire file and then write it out), which is what we recommend that you use. Another key reason for the popularity of line-delimited JSON is because JSON objects have structure, and JavaScript (on which JSON is based) has at least basic types. This makes it easier to work with because Spark can make more assumptions on our behalf about the data.   Read/write Key Potential values Default Description Both compression or codec None, uncompressed, bzip2, deflate, gzip, lz4, or snappy none Declares what compression codec Spark should use to read or write the file. Both dateFormat Any string or character that conforms to Java’s SimpleDataFormat. yyyy-MM-dd Declares the date format for any columns that are date type. Both timestampFormat Any string or character that conforms to Java’s SimpleDataFormat. yyyy-MM-dd’T’HH:​mm:ss.SSSZZ Declares the timestamp format for any columns that are timestamp type. Read primitiveAsString true, false false Infers all primitive values as string type. Read allowComments true, false false Ignores Java/C++ style comment in JSON records. Read allowUnquotedFieldNames true, false false Allows unquoted JSON field names. Read allowSingleQuotes true, false true Allows single quotes in addition to double quotes. Read allowNumericLeadingZeros true, false false Allows leading zeroes in numbers (e.g., 00012). Read allowBackslashEscapingAnyCharacter true, false false Allows accepting quoting of all characters using backslash quoting mechanism. Read columnNameOfCorruptRecord Any string Value of spark.sql.column&NameOfCorruptRecord Allows renaming the new field having a malformed string created by permissive mode. This will override the configuration value. Read multiLine true, false false Allows for reading in non-line-delimited JSON files. Following shows an example of reading from csv files and writing to JSON file 1    import org.apache.spark.sql._ 2    import org.apache.spark.sql.types._ 3    4    object SparkDefinitiveTesting { 5    6      def main(args: Array[String]): Unit = { 7        val spark = SparkSession.builder().master("local[*]").appName("Test App").getOrCreate() 8        spark.sparkContext.setLogLevel("FATAL") 9    10       val manualSchema = StructType(Seq(StructField("InvoiceNo", StringType, true), 11         StructField("StockCode", StringType, true), 12         StructField("Description", StringType, true), 13         StructField("Quantity", IntegerType, true), 14         StructField("InvoiceDate", TimestampType, true), 15         StructField("UnitPrice", DoubleType, true), 16         StructField("CustomerID", DoubleType, true), 17         StructField("Country", StringType, true))) 18   19       val df_csv_manual = spark.read.format("csv").option("header", "true").option("mode", "FAILFAST").option("inferSchema", "true").schema(manualSchema).load("C:\\Users\\sukulma\\Downloads\\Spark-Data\\Spark-data\\data\\retail-data\\by-day").repartition(5) 20       println("Count of Dataframe df_csv_manual:" + df_csv_manual.count()) 21       df_csv_manual.write.format("json").mode(SaveMode.Overwrite).save("C:\\Users\\sukulma\\Downloads\\Spark-Data\\Spark-data\\data\\retail-data\\jsonop") 22   23   24     } 25   } C:\Users\sukulma\Downloads\Spark-Data\Spark-data\data\retail-data\jsonop>dir  Volume in drive C is OSDisk  Volume Serial Number is C05C-4437  Directory of C:\Users\sukulma\Downloads\Spark-Data\Spark-data\data\retail-data\jsonop 04/15/2019  01:16 AM    <DIR>          . 04/15/2019  01:16 AM    <DIR>          .. 04/15/2019  01:16 AM           173,680 .part-00000-f95a066d-d8a1-46fe-b07d-6cde56b4d2b8.json.crc 04/15/2019  01:16 AM           173,668 .part-00001-f95a066d-d8a1-46fe-b07d-6cde56b4d2b8.json.crc 04/15/2019  01:16 AM           173,684 .part-00002-f95a066d-d8a1-46fe-b07d-6cde56b4d2b8.json.crc 04/15/2019  01:16 AM           173,700 .part-00003-f95a066d-d8a1-46fe-b07d-6cde56b4d2b8.json.crc 04/15/2019  01:16 AM           173,676 .part-00004-f95a066d-d8a1-46fe-b07d-6cde56b4d2b8.json.crc 04/15/2019  01:16 AM                 8 ._SUCCESS.crc 04/15/2019  01:16 AM        22,229,808 part-00000-f95a066d-d8a1-46fe-b07d-6cde56b4d2b8.json 04/15/2019  01:16 AM        22,228,436 part-00001-f95a066d-d8a1-46fe-b07d-6cde56b4d2b8.json 04/15/2019  01:16 AM        22,230,267 part-00002-f95a066d-d8a1-46fe-b07d-6cde56b4d2b8.json 04/15/2019  01:16 AM        22,232,349 part-00003-f95a066d-d8a1-46fe-b07d-6cde56b4d2b8.json 04/15/2019  01:16 AM        22,229,060 part-00004-f95a066d-d8a1-46fe-b07d-6cde56b4d2b8.json 04/15/2019  01:16 AM                 0 _SUCCESS               12 File(s)    112,018,336 bytes                2 Dir(s)  77,656,604,672 bytes free Sample output file:   {"InvoiceNo":"580538","StockCode":"22467","Description":"GUMBALL COAT RACK","Quantity":6,"InvoiceDate":"2011-12-05T08:38:00.000-05:00","UnitPrice":2.55,"CustomerID":14075.0,"Country":"United Kingdom"} {"InvoiceNo":"580539","StockCode":"84030E","Description":"ENGLISH ROSE HOT WATER BOTTLE","Quantity":4,"InvoiceDate":"2011-12-05T08:39:00.000-05:00","UnitPrice":4.25,"CustomerID":18180.0,"Country":"United Kingdom"} {"InvoiceNo":"580539","StockCode":"23235","Description":"STORAGE TIN VINTAGE LEAF","Quantity":12,"InvoiceDate":"2011-12-05T08:39:00.000-05:00","UnitPrice":1.25,"CustomerID":18180.0,"Country":"United Kingdom"} {"InvoiceNo":"580539","StockCode":"22375","Description":"AIRLINE BAG VINTAGE JET SET BROWN","Quantity":4,"InvoiceDate":"2011-12-05T08:39:00.000-05:00","UnitPrice":4.25,"CustomerID":18180.0,"Country":"United Kingdom"} Note that one file per partition is  written out, and the entire DataFrame will be written out as a folder. It will also have one JSON object per line.