[SOLVED] JSON vs. REGEX

Setup, Configuration and Use Beginners
1

I have a json response which looks like:

{
    "tid": "volvo",
    "lat": xxx,
    "_type": "location",
    "t": "p",
    "_vehicle": {
        "ERS": {
            "engineStartWarning": "None",
            "timestamp": "2018-05-11T05:22:53+00:00",
            "status": "off",
            "engineStartWarningTimestamp": "2018-05-11T05:22:53+00:00"
        },
        "VIN": "xxx",
        "assistanceCallSupported": true,
        "averageFuelConsumption": 82.0,
        "averageFuelConsumptionTimestamp": "2018-05-11T05:24:26+00:00",
        "averageSpeed": 74,
        "averageSpeedTimestamp": "2018-05-11T05:24:26+00:00",
        "bCallAssistanceNumber": "xxx",
        "brakeFluid": "Normal",
        "brakeFluidTimestamp": "2018-05-11T05:24:26+00:00",
        "bulbFailures": [],
        "bulbFailuresTimestamp": "2018-05-11T05:24:26+00:00",
        "calculatedPosition": {
            "longitude": null,
            "speed": null,
            "timestamp": null,
            "heading": null,
            "latitude": null
        },

I would like to extract “heading”

With JSONPATH I used:
val String head = transform("JSONPATH", "$._vehicle.calculatedPosition.heading", json)

However, this returns " null"
I would prefer “null”

I also tried with REGEX:
val String head = transform(“REGEX”, ““calculatedPosition”: {\s.,\s.,\s.,\s.“heading”: (.*),”, json)

Which works in an online REGEX tester, but not in OH:
Configuration model 'car.rules' has errors, therefore ignoring it: [63,55]: Invalid escape sequence (valid ones are \b \t \n \f \r \" \' \\ )

Any suggestion to solve this the best way?
I could use " null" in rules - but that’s kind of “dirty”

2 
var String head = transform("JSONPATH", "$._vehicle.calculatedPosition.heading", json)
head = head.trim()

You can try:

val String head = transform("JSONPATH", "$._vehicle.calculatedPosition.heading", json).trim()

But I am not sure that will work

3

thanks for your lightning fast response :slight_smile:
I will give it a try.

4

I actually found another issue.

If the JSON online tester returns >null< openhab stores the entire json string instead of >null<
Is this a known issue or my problem only?

5

No it’s not a know error, it’s by design
You will probably be better of with a JS transform

6

Hmmm, ok, thanks.
How would this look like vs the JSONPATH stuff?

7

Create a file called volvoheading.js in your transform folder
with the following content:

(function(volvo) {
var data = JSON.parse(volvo);
var heading = data._vehicle.calculatedPosition.heading;
return heading.trim();
})(input)

But the value returned is a STRING of value “null” which OH could interpret as NULL. Maybe.
So you could change the value of null in the script to 999, or whatever…

if (heading == "null") {
    return = 999;
}

Your code now becomes:

val Number head = transform(“JS”, "volvoheading.js", json)
1 Like
8

Thank you so much.

The part of if (heading == "null") { I tried with JSONPATH already, but in that case it did not help.

I will be able to manage this now with JS.
Thanks again!

9

That’s better:

(function(volvo) {
var data = JSON.parse(volvo);
var heading = data._vehicle.calculatedPosition.heading.trim();
if (heading == "null") {
    return "999";
}
return heading;
})(input)
10

Is it maybe:

if (heading == “null”) {
heading = 999;
}

like:

(function(volvo) {
var data = JSON.parse(volvo);
var heading = data._vehicle.calculatedPosition.heading.trim();
if (heading == "null") {
    heading = 999;
}
return heading;
})(input)

because I still get :
[ERROR] [ore.transform.actions.Transformation] - Error executing the transformation ‘JS’: An error occurred while executing script.

11

Don’t you need to use === instead of == when comparing to “null” in java?

12

Yes that was a bad typo.
I wanted to avoid type conflict
return 999;
Or
heading = “999”;

13

In this case it the string “null” that we are checking not the null value.

14

I see that now, my bad!

15

doesn’t help.
I stll get the entire json response back :frowning:

16

The regex is embeded in a string thus all stated characters in the error message have to be escaped.
UPDATED:This works for me.

val String head = transform("REGEX", ".*\"heading\".*:\\s(.*),", json)

As for the JSONPATH

rule "Test JSONPATH"
    when
        Item Test_1 received command
    then
        logInfo("JSON Test","Start")
        var json ="{ \"tid\": \"volvo\", \"lat\": xxx, \"_type\": \"location\", \"t\": \"p\", \"_vehicle\": { \"ERS\": { \"engineStartWarning\": \"None\", \"timestamp\": \"2018-05-11T05:22:53+00:00\", \"status\": \"off\", \"engineStartWarningTimestamp\": \"2018-05-11T05:22:53+00:00\" }, \"VIN\": \"xxx\", \"assistanceCallSupported\": true, \"averageFuelConsumption\": 82.0, \"averageFuelConsumptionTimestamp\": \"2018-05-11T05:24:26+00:00\", \"averageSpeed\": 74, \"averageSpeedTimestamp\": \"2018-05-11T05:24:26+00:00\", \"bCallAssistanceNumber\": \"xxx\", \"brakeFluid\": \"Normal\", \"brakeFluidTimestamp\": \"2018-05-11T05:24:26+00:00\", \"bulbFailures\": [], \"bulbFailuresTimestamp\": \"2018-05-11T05:24:26+00:00\", \"calculatedPosition\": { \"longitude\": null, \"speed\": null, \"timestamp\": null, \"heading\": null, \"latitude\": null },}}"
        val result = transform("JSONPATH","$._vehicle.calculatedPosition.heading" ,json)
        logInfo("JSON Test","Result:" + result )
end

Gives me following log:

[INFO ] [pse.smarthome.model.script.JSON Test] - Result:NULL

The postet JSONSTRING is missing two termination brackets }}. but then it returns what you wanted, imho.

You get the whole string back when there is no match in the string for your query.

17

Thanks - I will play around with your suggestions.

About the two brackets:
I have cut off most of the stuff below to keep it short.
so the original json string was much longer.

18

I guess the main issue are the newlines in the json string.

Escaping the \s to \s like
val String head1 = transform("REGEX", "\"calculatedPosition\": {\\s.*,\\s.*,\\s.*,\\s.*\"heading\": (.*),", json)

brings:

  `Error during the execution of rule 'request car information': Illegal repetition near index 12 ^"calculatedPosition ": {\s.*,\s.*,\s.*,\s.*"heading": (.*),$`

Isn’t there an option to look for the next “heading” after calculatedPosition regardless of the number of newlines?

19

I’ll try it in the morning

20

This is tested and it works

(function(volvo) {
var data = JSON.parse(volvo);
var heading = data._vehicle.calculatedPosition.heading;
if (heading === null) {
    heading = 999;
}
return heading;
})(input)