Example: Reading a JSON file

This example shows two ways to read a JSON file.

Example: JSON parsing and serializing directly

This program reads JSON data from customers.json. In this example, it loads the file into the reader object and advances to the first token. The JSONToVariable method is called to serialize the data and fill the program array custlist directly. Then the record content is written to the standard output.

A TRY/CATCH block is used to detect potential JSON format errors in the source file.

IMPORT json

DEFINE custlist DYNAMIC ARRAY OF RECORD
            num INTEGER,
            name VARCHAR(40)
         END RECORD

DEFINE reader json.JSONReader
DEFINE ind INTEGER

MAIN
    TRY
        LET reader = json.JSONReader.Create()
        CALL reader.setInputCharset("UTF-8")
        CALL reader.readfrom("customers.json")
        CALL reader.next()
        DISPLAY "Start parsing "
        CALL json.Serializer.JSONToVariable(reader,custlist)
        FOR ind = 1 to custlist.getLength()
            DISPLAY custlist[ind].*
        END FOR
        CALL reader.close()
    CATCH
        DISPLAY "JSON Serializer ERROR: shouldn't raise error :",
        status || " " || sqlca.sqlerrm
        EXIT PROGRAM -1
    END TRY
    DISPLAY "parsing complete"
END MAIN

The file customers.json:

[
   {
        "num": 823,
        "name": "Mark Renbing"
    }, {
        "num": 234,
        "name": "Clark Gambler"
    }
]

The output:

Start parsing 
        823Mark Renbing
        234Clark Gambler
parsing complete

Example: event type JSON parsing

This program reads JSON data from client.json. Use this example to control end-to-end JSON parsing. The program loads the file into the reader object. The main loop will parse the file by checking the event type as it reads the file.

A TRY/CATCH block is used to detect potential JSON format errors in the source file.

IMPORT json
IMPORT util

DEFINE reader json.JSONReader
DEFINE str STRING

MAIN

    DEFINE startReadClient BOOLEAN
    DEFINE array BOOLEAN
    DEFINE nextElement BOOLEAN

    TRY
        LET reader = json.JSONReader.Create()
        CALL reader.setInputCharset("UTF-8")
        CALL reader.readfrom("client.json")
        DISPLAY "Hello ! Welcome to your client analyzer :) \n"
        WHILE reader.hasnext()
            CASE reader.getEventType()
                WHEN "START_DOCUMENT"
                    DISPLAY "Start reading data.. \n"
                    DISPLAY "loading ||"
                    DISPLAY "loading ||||"
                    DISPLAY "loading ||||||||||"
                    CALL reader.next()
                WHEN "START_OBJECT"
                    IF NOT startReadClient THEN
                        DISPLAY "\n---------- New client discovered: ----------\n"
                        LET startReadClient = TRUE
                    END IF
                    CALL reader.next()
                WHEN "END_OBJECT"
                    DISPLAY "\n"
                    CALL reader.next()
                WHEN "START_ARRAY"
                    CALL reader.next()
                WHEN "END_ARRAY"
                    CALL reader.next()
                WHEN "PROPERTY"
                    LET str = reader.getProperty()
                    CASE
                        WHEN reader.getProperty().equalsIgnoreCase("name")
                            DISPLAY "Name: "
                        WHEN reader.getProperty().equalsIgnoreCase("firstname")
                            CALL reader.next()
                            DISPLAY "   Firstname: ", reader.getValue()
                        WHEN reader.getProperty().equalsIgnoreCase("lastname")
                            CALL reader.next()
                            DISPLAY "   Lastname: ", reader.getValue()
                        WHEN reader.getProperty().equalsIgnoreCase("sex")
                            CALL reader.next()
                            DISPLAY "Sex: ", reader.getValue()
                            DISPLAY "\n"
                        WHEN reader.getProperty().equalsIgnoreCase("address")
                            DISPLAY "Address: ", reader.getValue()
                        WHEN reader.getProperty().equalsIgnoreCase("streetAddress")
                            CALL reader.next()
                            DISPLAY "   StreetAddress: ", reader.getValue()
                        WHEN reader.getProperty().equalsIgnoreCase("City")
                            CALL reader.next()
                            DISPLAY "   City: ", reader.getValue()
                        WHEN reader.getProperty().equalsIgnoreCase("State")
                            CALL reader.next()
                            DISPLAY "   State: ", reader.getValue()
                        WHEN reader.getProperty().equalsIgnoreCase("phoneNumber")
                            DISPLAY "PhoneNumber: "
                        WHEN reader.getProperty().equalsIgnoreCase("type")
                            CALL reader.next()
                            DISPLAY "   Type: ", reader.getValue()
                            WHEN reader.getProperty().equalsIgnoreCase("number")
                            CALL reader.next()
                            DISPLAY "   number: ", reader.getValue()
                    END CASE
                    CALL reader.next()
                WHEN "STRING"
                    CALL reader.next()
                WHEN "NUMBER"
                    CALL reader.next()
                WHEN "BOOLEAN"
                    CALL reader.next()
                WHEN "NULL"
                    DISPLAY "Null"
                    CALL reader.next()
                WHEN "END_DOCUMENT"
                    DISPLAY "\n..end of treatment"
                    EXIT WHILE
                OTHERWISE
                    DISPLAY "json data not recognized"
                    EXIT PROGRAM -1
            END CASE
        END WHILE
    CATCH
        DISPLAY "JSON Serializer ERROR: shouldn't raise error :",
            status || " " || sqlca.sqlerrm
        EXIT PROGRAM -1
    END TRY
    CALL reader.close()
END MAIN

The file client.json:

{
    "name": {
      "firstname": "Pierre",
      "lastname": "Kant"
    },
    "age": 32,
    "sex": "Male",
    "address": {
        "streetAddress": "45 Rue de Londre",
        "City": "Toulouse",
        "State": "France",
        "postalCode":31555
      },
    "phoneNumber": [
        {
            "type": "home",
            "number": "555 555 555"
        },
        {
            "type": "mobile",
            "number": "556 556 556"
        }
    ]
}

The output:

Start reading data..

loading ||
loading ||||
loading ||||||||||

---------- New client discovered: ----------

Name:
   Firstname: Pierre
   Lastname: Kant

Sex: Male

Address:
   StreetAddress: 45 Rue de Londre
   City: Toulouse
   State: France

PhoneNumber:
   Type: home
   number: 555 555 555

   Type: mobile
   number: 556 556 556