Decode JSON webservice reply data (already stored in IFS) using YAJL
This reads the JSON from the IFS – decodes it using Y.A.J.L and reports on time taken to perform decode. Writing an RPG program to read JSON using YAJL is actually pretty straightforward — I hope this code example helps!
In this case the JSON data is a simple layout that looks like this:
USERID varchar(100);
FIRSTNAME varchar(100);
LASTNAME varchar(100);
INITIALS varchar(100);
COMPANY int(10);
DIVISION int(10);
DEPARTMENT int(10);
So. lets read it and break it out into fields, which I am just storing in an array. You could write them to a file just as easily…
**FREE
/TITLE JSON_TABLE Decode JSON using Y.A.J.L. - Proof of Concept
// ------------------------------------------------------
// PROGRAM CREATION OVERRIDES:
//
// Create as a Module and bind into ILE program
//
// JSNIFSYAJL.sqlrpgle (fully /free)
//
// This demonstrates reading JSON data from an IFS file and then
// parsing that JSON to break out the subffields using Y.A.J.L.
// Subfields within the objects are retrieved by their field names.
//
// The JSON data is loaded into a data structure suitable
// for display from a program debugger.
//
// Compile - ADDLIBLE : LITTENN LMDTA06NL YAJL
//
// Check input data -
// DSPLNK OBJ( ** value from IFSFilename ** )
//
// MODIFICATION HISTORY:
//
// 07/17/2017 nick.litten V1.00
//
ctl-opt dftactgrp(*no) actgrp('LITTENN')
option(*nodebugio:*srcstmt:*nounref)
bnddir('YAJL') alwnull(*inputonly)
datfmt(*ISO) decedit('0.')
copyright('| JSNIFSYAJL 1.0 06/27/2017 Use YAJL to read JSON from IFS and Parse.');
/include yajl_h
// IFS file with JSON code that we will be reading and decoding
dcl-c ifsFilename
const('/littenn/getwebjsn.json');
dcl-ds jsonFields qualified template;
USERID varchar(100);
FIRSTNAME varchar(100);
LASTNAME varchar(100);
INITIALS varchar(100);
COMPANY int(10);
DIVISION int(10);
DEPARTMENT int(10);
end-ds;
dcl-ds result qualified;
success ind;
errmsg varchar(500);
jsonArray likeds(jsonFields) dim(9999);
end-ds;
dcl-s docNode like(yajl_val);
dcl-s list like(yajl_val);
dcl-s node like(yajl_val);
dcl-s val like(yajl_val);
dcl-s Count int(10);
dcl-s lastElement int(10) inz;
dcl-s errMsg varchar(500) inz('');
dcl-s strTimeStamp timestamp inz; // start of pgm
dcl-s strJsonTimeStamp timestamp inz; // start of JSON decode logic
dcl-s endTimeStamp timestamp inz; // used to calculate duration
// Parms for logging-text being sent back into program message queue
dcl-pr QMHSNDPM extpgm('QMHSNDPM');
*n char(7) const; // MsgID
*n char(20) const; // MsgFile
*n char(32767) const options(*varsize); // MsgData
*n int(10) const; // MsgDtaLen
*n char(10) const; // MsgType
*n char(10) const; // StackEntry
*n int(10) const; // StackCount
*n char(4); // MsgKey
*n char(32767) options(*varsize); // ErrorCode
end-pr;
dcl-ds ErrorCode;
BytesProv int(10) inz(0);
BytesAvail int(10) inz(0);
end-ds;
dcl-s joblogMsg char(200);
dcl-s MsgKey char(4);
/Title [---------- MAINLINE ---------- ]
strTimeStamp=%timestamp();
// Load JSON in from the IFS file using YAJL
docNode = yajl_stmf_load_tree( ifsFilename : errMsg );
// If it loaded then lets decode it:
if errMsg = '';
strJsonTimeStamp=%timestamp();
// Write the JSON *header* level values
node = YAJL_object_find(docNode: 'success');
result.success = YAJL_is_true(node);
node = YAJL_object_find(docNode: 'errmsg');
result.errmsg = YAJL_get_string(node);
list = YAJL_object_find(docNode: 'users');
// Write the JSON *data array* level values
Count = 0;
dow YAJL_ARRAY_LOOP( list: Count: node );
lastElement = Count;
val = YAJL_object_find(node: 'userID');
result.jsonArray(Count).userID = yajl_get_string(val);
val = YAJL_object_find(node: 'firstName');
result.jsonArray(Count).firstName = yajl_get_string(val);
val = YAJL_object_find(node: 'lastName');
result.jsonArray(Count).lastName = yajl_get_string(val);
val = YAJL_object_find(node: 'initials');
result.jsonArray(Count).initials = yajl_get_string(val);
val = YAJL_object_find(node: 'company');
result.jsonArray(Count).company = yajl_get_number(val);
val = YAJL_object_find(node: 'division');
result.jsonArray(Count).division = yajl_get_number(val);
val = YAJL_object_find(node: 'department');
result.jsonArray(Count).department = yajl_get_number(val);
enddo;
yajl_tree_free(docNode);
// Set Ending timestamps and calculate runtime
endTimeStamp=%timestamp();
joblogMsg = 'JSNIFSYAJL Completed with ' +
%char(lastElement) +
' elements. Total runtime:' +
%char(%diff(endTimeStamp:strTimeStamp:*mseconds)) +
' YAJL DECODE only:' +
%char(%diff(endTimeStamp:strJsonTimeStamp:*mseconds)) ;
// stick that message into the joblog so we can clearly see the runtime
QMHSNDPM( 'CPF9897'
: 'QCPFMSG *LIBL'
: joblogMsg
: %len(%trimr(joblogMsg))
: '*DIAG'
: '*'
: 0
: MsgKey
: ErrorCode );
else;
// If unable to load JSON data from the IFS then tell the world
result.success = *off;
result.errmsg = 'Bugger! I couldnt read the IFS file';
endif;
*inlr = *on;
So what does this do?
(1) reads the JSON from the input IFS File
(2) Stores a timestamp
(3) decodes the JSON and stores all the values in an array
(4) sends a message to the joblog saying how long it took.
In this case :
call JSNIFSYAJL
JSNIFSYAJL Completed with 91 elements. Total runtime:11000 YAJL DECODE
only:4000
#prettydarnquick
[thrive_split_button left_color=”orange” right_color=”purple” left_text=”Decode JSON using YAJL” right_text=”Decode JSON using SQL and JSON_TABLE” left_link=”https://www.nicklitten.com/rpg-example-reading-json-using-yajl-ifs/” right_link=”https://www.nicklitten.com/rpg-example-reading-json-using-json_table-from-ifs/”]
IBM i Software Developer, Digital Dad, AS400 Anarchist, RPG Modernizer, Shameless Trekkie, Belligerent Nerd, Englishman Abroad and Passionate Eater of Cheese and Biscuits.
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