bvstone

Parsing JSON using RPG with Scott Klement's Port of YAJL (Yet Another JSON Library) - Part 4

Posted:

Parsing JSON using RPG with Scott Klement's Port of YAJL (Yet Another JSON Library) - Part 4

We are so excited about the YAJL JSON parser port that we decided to throw together an online demo for it (which there is a link to at the end of this article).

We already had one set up for our JSONTOOL parser, but since we've decided to move all future development over to use the YAJL parser we thought we better put something together for it as well.

One issue we ran into when putting together the YAJL parsing demo was we didn't have a way to say "get this value" from the JSON.  When we built our JSON parser we had a slightly different interaction method than with the YAJL parser.

For our parser we used the format:

node[index]:node[index]...

This means that we would use a node name followed by an optional index, and then followed by optional nodes down the line.  So, we need to convert this notation so that it returns the correct node from the JSON data when we are parsing it with the YAJL parser.

What we came up with was the following:

     H DFTACTGRP(*NO) BNDDIR('ERPGSDK') BNDDIR('YAJL')
      ****************************************************************
      * Imports
      ****************************************************************
      /include yajl_h
      ****************************************************************
      * Prototypes                                                   *
      ****************************************************************
      /COPY QCOPYSRC,P.ERPGSDK
      /COPY QCOPYSRC,P.HTTPSTD
      ****************************************************************
      * Local Prototypes                                             *
      ****************************************************************
     D #getNode        PR              *
     D  InString                  65535    Value Varying
      *
     D #getNodeIndex   PR            10i 0
     D  InOutString               65535    Varying
      ****************************************************************
      * Data read in from web page
     D variable        S           1024    Varying
     D json            S          65535
      *
      * Work Variables
     D docNode         s                   like(yajl_val)
     D node            s                   like(yajl_val)
      *
     D errMsg          s            500a   Varying
      *
     D data            S          65535    Varying
     D dataSize        S             10i 0
      ****************************************************************
      /free
       #startup();
       #setImmediate(*ON);
       #writeTemplate('stdhtmlheader.erpg');
       variable = #getData('variable');
       json = #getData('json');

       if (json <> ' ');
         docNode = yajl_buf_load_tree(%addr(json):%len(%trimr(json)):errMsg );

         if (docNode <> *NULL);
           #WrStout('JSON Size=' + %char(%len(%trimr(json))) + '<br>');

           node = #getNode(variable);
           data = ' ';
           dataSize = 0;

           select;
           when (YAJL_IS_STRING(node));
             data = yajl_get_string(node);
           when (YAJL_IS_NUMBER(node));
             data = %char(yajl_get_number(node));
           when (YAJL_IS_TRUE(node));
             data = 'true';
           when (YAJL_IS_FALSE(node));
             data = 'false';
           when (YAJL_IS_OBJECT(node));
             data = 'JSON Object';
             dataSize = YAJL_OBJECT_SIZE(node);
           endsl;

           if (dataSize = 0);
             dataSize = %len(data);
           endif;

           #WrStout('Object Value=' + data + '<br>');
           #WrStout('Object Size=' + %char(dataSize) + '<br>');
         endif;

       else;
         errMsg = 'No JSON data';
       endif;

       #WrStout('Error=' + errMsg + '<br>');

       yajl_tree_free(docNode);
       #cleanup();

       *INLR = *on;
      /end-free
      *//////////////////////////////////////////////////////////////*
      * #getNode - Get the Node Requested                            *
      *                                                              *
      * Input:                                                       *
      *   InString - The String representing the node to retrieve.   *
      *               If the JSON string starts as an array, use     *
      *               ROOT[index] as the first part of the request.  *
      *                                                              *
      *              examples:                                       *
      *              customerList[1]:firstName                       *
      *              ROOT[2]:firstName                               *
      *              data:color                                      *
      *                                                              *
      * Returns:                                                     *
      *   Pointer to node requested                                  *
      *                                                              *
      *//////////////////////////////////////////////////////////////*
     P #getNode        B                   EXPORT
      *--------------------------------------------------------------*
     D #getNode        PI              *
     D  InString                  65535    Value Varying
      *--------------------------------------------------------------*
     D i               S             10i 0
     D j               S             10i 0
     D curTag          S          65535    Varying
     D curTagIndex     S             10i 0
     D localNode       S                   like(yajl_val)
      *--------------------------------------------------------------*
      /free
       i = %scan(':':InString);
       j = 1;
       localNode = docNode;

       dow (i > 0);

         if (i > j); //Do this in case someone puts :: in the string
           curTag = %subst(InString:j:i-j);
           exsr $GetPointer;
         endif;

         j = (i + 1);
         i = %scan(':':InString:j);
       enddo;

       curTag = %subst(InString:j);
       exsr $GetPointer;

       return localNode;

       //*--------------------------------------------------------------*
       //* Get Pointer
       //*--------------------------------------------------------------*
       BegSr $GetPointer;

         curTagIndex = #getNodeIndex(curTag);

         select;
         when (curTagIndex < 0);
           errMsg = 'Error retrieving object index!';
           return *NULL;
         when (curTagIndex > 0);

           if (curTag <> 'ROOT');
             localNode = YAJL_object_find(localNode:curTag);
           endif;

           if (YAJL_IS_ARRAY(localNode));

             if (curTagIndex <= YAJL_ARRAY_SIZE(localNode));
               localNode = YAJL_ARRAY_ELEM(localNode:curTagIndex);
             else;
               errMsg = 'Index ' + %char(curTagIndex) +
                        ' out of range for ' + curTag + ' in ' +
                        variable + '.';
               return *NULL;
             endif;

           else;
             errMsg = curTag + ' is not an array.';
             return *NULL;
           endif;

         other;
           localNode = YAJL_object_find(localNode:curTag);

           if (YAJL_IS_ARRAY(localNode));
             errMsg = curTag + ' is an array.  Index ' +
                      %char(curTagIndex) + ' is invalid.';
             return *NULL;
           endif;

         endsl;

         if (localNode = *NULL);
             errMsg = curTag + ' not found in ' + variable + '.';
             return localNode;
         endif;

       EndSr;

       //*--------------------------------------------------------------*
       BegSr *PSSR;

         errMsg = 'getNode Internal error!';
         RETURN *NULL;

       EndSr;
       //*--------------------------------------------------------------*
      /end-free
     P #getNode        E
      *//////////////////////////////////////////////////////////////*
      * #getNodeIndex - Get The Index of the Node Requested          *
      *                                                              *
      * Input/Output:                                                *
      *   InOutString - The single node name with or without index   *
      *                  to retrieve the index for.                  *
      *                                                              *
      *                 examples:                                    *
      *                 customerList[1]                              *
      *                 ROOT[2]                                      *
      *                 color                                        *
      *                                                              *
      *                 This value will be returned minus the index  *
      *                  information when complete.                  *
      *                                                              *
      *                 examples:                                    *
      *                 customerList                                 *
      *                 ROOT                                         *
      *                 color                                        *
      *                                                              *
      * Returns:                                                     *
      *   Index of the item, -1 for error, 0 for a node name that    *
      *    does not contain an index.                                *
      *                                                              *
      *//////////////////////////////////////////////////////////////*
     P #getNodeIndex   B                   EXPORT
      *--------------------------------------------------------------*
     D #getNodeIndex   PI            10i 0
     D  InOutString               65535    Varying
      *--------------------------------------------------------------*
     D i               S             10i 0
     D j               S             10i 0
     D index           S             10i 0
      *--------------------------------------------------------------*
      /free
       index = 0;
       i = %scan('[':InOutString);
       j = 1;

       if (i > 1);
         i = (i + 1);
         j = %scan(']':InOutString:i);

         if (j > i);
           Monitor;
             index = %int(%subst(InOutString:i:j-i));
           On-Error;
             index = 1;
           EndMon;
         endif;

         InOutString = %subst(InOutString:1:i-2);
       endif;

       return index;

       //*--------------------------------------------------------------*
       BegSr *PSSR;

         return -1;

       EndSr;
       //*--------------------------------------------------------------*
      /end-free
     P #getNodeIndex   E

The basic functionality of this application is as follows:

  • Read in the JSON data
  • Read in the string that represents the node we want to retrieve the value for
  • Go through each node (separated by a colon) until we reach the end, then return a pointer to that last node
  • Retrieve the value of the node and display it

Most of the code included is used to parse the node string that is passed in.  For example, if we pass in the following node string:

customerList[2]:firstName

We first need to find the second customerList object.  Once we have that, we retrieve the firstName object from the specific customerList object.

That means looping through our input variable looking for a colon (:) until we find the end of the string.

For each object name in the input variable we retrieve the pointer to that specific node.  If the object is an array (denoted by [index]) that index is retrieved using the #getNodeIndex() subprocedure.  But, not only does this subprocedure return the index, it also updates the tag name and removes any array index from it.  So, if we sent in CustomerList[4] we will retrieve 4 as the index, and the object name is changed to CustomerList.

Once we've parsed our way down the JSON "tree" we end up with either a NULL value (which means the JSON object wasn't found) or a pointer to the JSON object which we can then use to retrieve the actual value from 

The demo can be see by clicking here.

Related Articles:


Last edited 10/06/2015 at 10:17:31



Latest Posts:

Non HTTPS Callbacks Removed from GreenTools for G Suite (G4G) Non HTTPS Callbacks Removed from GreenTools for G Suite (G4G)
Posted by April 15, 2018
BVSTools >> BVSTools Announcements >> GreenTools for G Suite (Google Apps) (G4G) Specific Announcements
IBM i Related Survey Available IBM i Related Survey Available
Posted by April 7, 2018
IBM Power Systems >> (QGPL) IBM i
BVSTools Releases Braintree Webhook Open Source Application - Node.js BVSTools Releases Braintree Webhook Open Source Application - Node.js
Posted by April 5, 2018
Programming >> Open Source
BVSTools Now Offering Web Services (BETA) BVSTools Now Offering Web Services (BETA)
Posted by April 3, 2018
BVSTools >> BVSTools Announcements
Creating a Reverse SSL Proxy Using RPG on the IBM i - Part 2 Creating a Reverse SSL Proxy Using RPG on the IBM i - Part 2
Posted by March 29, 2018
Programming >> Web Programming
Still on V7R1 or Earlier?  Here's Why You Should Upgrade NOW! Still on V7R1 or Earlier? Here's Why You Should Upgrade NOW!
Posted by February 21, 2018
IBM Power Systems >> (QGPL) IBM i
Converting a MMDDYY date format to YYMMDD for Sorting Using SQL Converting a MMDDYY date format to YYMMDD for Sorting Using SQL
Posted by February 16, 2018
Programming >> RPG Programming
Moving All Files from a Google Drive Folder to the Trash Using GreenTools for Google Apps (G4G) Moving All Files from a Google Drive Folder to the Trash Using GreenTools for Google Apps (G4G)
Posted by February 3, 2018
BVSTools >> BVSTools Software Discussion >> GreenTools for G Suite (Google Apps) (G4G) Specific Discussion
Removing Unwanted Characters from a String with RPG Removing Unwanted Characters from a String with RPG
Posted by February 2, 2018
Programming >> RPG Programming
GETURI Version 8.10 Released GETURI Version 8.10 Released
Posted by January 23, 2018
BVSTools >> BVSTools Announcements >> Get URI (GETURI) Specific Announcements
BVSTools is Now a Sponsor of ALLAS400S.com BVSTools is Now a Sponsor of ALLAS400S.com
Posted by January 17, 2018
BVSTools >> BVSTools Announcements
Service Pack SP171219 Released for G4PP v3.10 Service Pack SP171219 Released for G4PP v3.10
Posted by December 20, 2017
BVSTools >> BVSTools Announcements >> GreenTools for PayPal (G4PP) Specific Announcements
GETURI Now Requires Minimum OS of V7R1 or Higher GETURI Now Requires Minimum OS of V7R1 or Higher
Posted by December 12, 2017
BVSTools >> BVSTools Software Discussion >> Get URI (GETURI) Specific Discussion
Need Help Updating Your Software Versions?  We Can Help. Need Help Updating Your Software Versions? We Can Help.
Posted by December 8, 2017
BVSTools >> BVSTools Announcements
Parsing the Response from GreenTools for PayPal (G4PP) Refund Transaction Parsing the Response from GreenTools for PayPal (G4PP) Refund Transaction
Posted by November 27, 2017
BVSTools >> BVSTools Software Discussion >> GreenTools for PayPal (G4PP) Specific Discussion

Reply




Copyright 1983-2018 BVSTools
GreenBoard(v3) Powered by the eRPG SDK, MAILTOOL Plus!, GreenTools for Google Apps, jQuery, jQuery UI, BlockUI, CKEditor and running on the IBM i (AKA AS/400, iSeries, System i).