How to retrieve Data from JSON file (Web Request)?
lazarus / 38-Networking and Web Programming

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MrMaxMusterman · 2021-05-21 21:46

I have a question concerning retrieving data from a JSON file with i
get by a URL request.
I already have a few code snippets together from other forum articles
(see below)


Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject);var  Http:TFPHttpClient; 
Content:String;  Json:TJSONData;  Lat:string;begin 
 Http:=TFPHttpClient.Create(Nil);   try   
 Content:=Http.Get('https://www.mywebsite.com');   
 JSON:=GetJSON(Content);     try       //Retrieving Data from JSON   
 finally     end;   finally   end;end;
My question now becomes how i'm now able to retrieve data from the
JSON File. Down below, i have the whole JSON File which is displayed
when requesting the desired URL

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i { 
 "results" : [      {         "address_components" : [            {  
           "long_name" : "20",               "short_name" : "20",    
         "types" : [ "street_number" ]            },            {    
         "long_name" : "West 34th Street",               "short_name"
: "W 34th St",               "types" : [ "route" ]            },     
     {               "long_name" : "Manhattan",             
 "short_name" : "Manhattan",               "types" : [ "political",
"sublocality", "sublocality_level_1" ]            },            {    
         "long_name" : "New York",               "short_name" : "New
York",               "types" : [ "locality", "political" ]           
},            {               "long_name" : "New York County",       
      "short_name" : "New York County",               "types" : [
"administrative_area_level_2", "political" ]            },           
{               "long_name" : "New York",               "short_name" :
"NY",               "types" : [ "administrative_area_level_1",
"political" ]            },            {               "long_name" :
"USA",               "short_name" : "US",               "types" : [
"country", "political" ]            },            {             
 "long_name" : "10118",               "short_name" : "10118",        
     "types" : [ "postal_code" ]            }         ],       
 "formatted_address" : "20 W 34th St, New York, NY 10118, USA",      
 "geometry" : {            "location" : {               "lat" :
40.748558,               "lng" : -73.9857578            },           
"location_type" : "ROOFTOP",            "viewport" : {             
 "northeast" : {                  "lat" : 40.74990698029149,         
       "lng" : -73.98440881970849               },             
 "southwest" : {                  "lat" : 40.74720901970849,         
       "lng" : -73.98710678029151               }            }       
 },         "place_id" : "ChIJr92XCKlZwokRIy2j_7Rb2V8",       
 "plus_code" : {            "compound_code" : "P2X7+CM New York City,
New York, USA",            "global_code" : "87G8P2X7+CM"         },  
     "types" : [ "street_address" ]      }   ],   "status" : "OK"}
In my case, I want to retrieve the "lat" and "lng" values out of the
JSON File.

I would really appreciate your help with this. Thanks in advance.

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zamronypj · 2021-05-21 23:43

https://wiki.freepascal.org/fcl-json

Code: [Select]lat :=
json.FindPath('results[0].geometry.location.lat').AsFloat;
lon := json.FindPath('results[0].geometry.location.lng').AsFloat;

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engkin · 2021-05-22 00:02

Or:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i var 
location:TJSONObject;  lat,lng:Single;... 
location:=TJSONObject(Json.FindPath('results[0].geometry.location')); 
lat:=location.Floats['lat'];  lng:=location.Floats['lng'];

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MrMaxMusterman · 2021-05-22 08:47

First off, thanks for your help.

I tried implementing all this but sadly, i always get EHTTPClient
Exeption Class due to Status Code 400.

Idk why but just to make things clear, its an https website with a
JSON File being hosted on.
Did I maybe forget something under the "uses" category or so?

Here is my full source code:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics, Dialogs, StdCtrls, fphttpclient, fpjson,
jsonparser, opensslsockets; type   { TForm1 }   TForm1 = class(TForm) 
  Button1: TButton;    Edit1: TEdit;    Label1: TLabel;    Label2:
TLabel;    procedure Button1Click(Sender: TObject);  private  
public   end; var  Form1: TForm1; implementation {$R *.lfm} { TForm1
} procedure TForm1.Button1Click(Sender: TObject);var 
Client:TFPHttpClient;  Content:String;  Json:TJSONData; 
Lat,Lng:string;  Location:string;begin 
 Client:=TFPHttpClient.Create(Nil);   Client.AllowRedirect:=true; 
 Location:=Edit1.Text;   try   
 Content:=Client.Get('https://mywebsite'+Location+'APIKEY');   
 JSON:=GetJSON(Content);     try     
 Lat:=json.FindPath('results[0].geometry.location.lat').AsString;    
 Lng:=json.FindPath('results[0].geometry.location.lng').AsString;   
 finally     end;   finally   end;   Label1.Caption:=Lat; 
 Label2.Caption:=Lng;end; end.

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engkin · 2021-05-22 12:37

I don't see a missing unit.

HTTP code 400 means the server is not happy with your request.
Something is wrong with the request itself. Sometimes the server sends
a message to explain more.

Put the request you are sending here. Obsecure any sensitive data with
####

Edit:
Probably it wants a User Agent. Try adding:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  
Client.AddHeader('User-Agent', 'Mozilla/5.0 (compatible; fpweb)'); 
Client.AddHeader('Content-Type', 'application/json');
right after Client.AllowRedirect

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MrMaxMusterman · 2021-05-22 13:17

Sadly, your idea with adding a user agent etc. didnt work out. Here is
my full source code with the actual request:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics, Dialogs, StdCtrls, fphttpclient, fpjson,
jsonparser, opensslsockets; type   { TForm1 }   TForm1 = class(TForm) 
  Button1: TButton;    Button2: TButton;    Edit1: TEdit;    Label1:
TLabel;    Label2: TLabel;    procedure Button1Click(Sender:
TObject);  private   public   end; var  Form1:
TForm1; implementation {$R *.lfm} { TForm1 } procedure
TForm1.Button1Click(Sender: TObject);var  Client:TFPHttpClient; 
Content:String;  Json:TJSONData;  Lat,Lng:Single; 
Location:string;begin   Client:=TFPHttpClient.Create(Nil); 
 Client.AllowRedirect:=true;   Client.AddHeader('User-Agent',
'Mozilla/5.0 (compatible; fpweb)');   Client.AddHeader('Content-Type',
'application/json');   Location:=Edit1.Text;   try     Content:=Client
.Get('https://maps.googleapis.com/maps/api/geocode/json?address=
'+Location+' &key={MyAPIKey}');     JSON:=GetJSON(Content);     try  
   Lat:=json.FindPath('results[0].geometry.location.lat').AsFloat;   
  Lng:=json.FindPath('results[0].geometry.location.lng').AsFloat;   
 finally     end;   finally   end;   Label1.Caption:=FloatToStr(Lat); 
 Label2.Caption:=FloatToStr(Lng);end;end. 
The only thing i put out of this source code is my api key from
google. It isnt the problem though cause if im actually using the link
(so my request including an adress, which can be formatted in any way
possible) in my browser, ill get the full json file.

Can you mabye tell me how i can gain more info on the error message
itself? I only get "Project project1 got Exeption Class EHTTPPClient
with following message: Unexpected response status code:400"
(translated)

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engkin · 2021-05-22 13:52

Since it works in your browser, get the request your browser is
sending. Search for an Add On, Extension, or Plug In for your browser
that would let you see the request including the headers. Then simply
replicate it.

Search for "HTTP 400":
Here is one result


Edit:
I bet there is a cookie in your browser that needs to be sent as well.
You had the authorize your browser at somepoint.

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MrMaxMusterman · 2021-05-22 14:08

I actually found out why the program wasnt working the whole time...

The problem was that for some reason, Lazarus didnt convert spaces
between each Adress Info (e.g. Street Name and Street Number) that the
user would type into the edit box into a new request with no spaces
whatsoever.

Is there maybe a way to replace all empty spaces in a string
(userinput) with something else (e.g. commas)?

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engkin · 2021-05-22 14:37

Try using EncodeURLElement?

It turns
123 Street, City, State 12345
into
123%20Street,%20City,%20State%2012345

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MrMaxMusterman · 2021-05-22 16:24

Thank you so much!!

Now everything works as intended.