Unexpected character (g) at position 0 when trying to parse json - HttpResponseDecorator

Whenever I try to execute below script I keep getting error, saying unexpected character (g). Basically I want to be able to parse the json response and be able to get the upstream job name from it.

Script:

@Grapes([
        @Grab(group='org.codehaus.groovy.modules.http-builder', module='http-builder', version='0.7.1'),
        @Grab(group='commons-collections', module='commons-collections', version='3.2.1'),
        @Grab(group='org.jsoup', module='jsoup', version='1.10.2'),
        @Grab(group='org.json', module='json', version='20190722'),
        @Grab(group='com.googlecode.json-simple', module='json-simple', version='1.1.1')
])



import static groovyx.net.http.ContentType.*
import groovyx.net.http.HttpResponseException
import groovyx.net.http.RESTClient
import groovy.json.JsonSlurper
import groovy.json.JsonOutput
import java.net.*
import java.util.*
import org.json.simple.*
import org.json.simple.parser.JSONParser;


def getRestClient(){
    String jenkinsUrl="http://somedomainname:8080"
    def restClient = new RESTClient(jenkinsUrl)
    return restClient
}

def getJobsInfo(String jobname,RESTClient restClient){
    def requrl= '/job/'+jobname+'/lastBuild/api/json/?pretty=true'
    def response = restClient.get( path : requrl)
    return response
}

def writeToPropertyFile(){
    def jsonResponseObject = getJobsInfo("sampleJobName",getRestClient())
    println "\n\n\n\n\n Json String :----   "+ jsonResponseObject.toString()

    JSONParser jsonParser = new JSONParser();
    JSONObject jsonObject = (JSONObject) jsonParser.parse(jsonResponseObject.toString());

    JSONArray upstreamJobInfoArray = jsonObject.getJSONArray("causes");

    for (int i = 0; i < upstreamJobInfoArray.length(); i++) {
        JSONObject jobCauses = upstreamJobInfoArray.getJSONObject(i);
        String upstreamProjectName = jobCauses.getString("upstreamProject");
        println upstreamProjectName
    }
}

writeToPropertyFile()

Error :

 Json String :----   groovyx.net.http.HttpResponseDecorator@6b063470
Caught: Unexpected character (g) at position 0.
Unexpected character (g) at position 0.
        at org.json.simple.parser.Yylex.yylex(Yylex.java:610)
        at org.json.simple.parser.JSONParser.nextToken(JSONParser.java:269)
        at org.json.simple.parser.JSONParser.parse(JSONParser.java:118)
        at org.json.simple.parser.JSONParser.parse(JSONParser.java:81)
        at org.json.simple.parser.JSONParser.parse(JSONParser.java:75)
        at org.json.simple.parser.JSONParser$parse.call(Unknown Source)
        at getUpstreamJob.writeToPropertyFile(getUpstreamJob.groovy:39)
        at getUpstreamJob.run(getUpstreamJob.groovy:50)

EDIT 1 : START

JSON response that I am trying to parse :

{
    "_class": "hudson.model.FreeStyleBuild",
    "actions": [
        {
            "_class": "hudson.model.CauseAction",
            "causes": [
                {
                    "_class": "hudson.model.Cause$UpstreamCause",
                    "shortDescription": "Started by upstream project \"sampleJobName\" build number 712",
                    "upstreamBuild": 712,
                    "upstreamProject": "sampleJobName",
                    "upstreamUrl": "job/sampleJobName/"
                },
                {
                    "_class": "hudson.model.Cause$UserIdCause",
                    "shortDescription": "Started by user Malick, Asif",
                    "userId": "asifma00",
                    "userName": "Malick, Asif"
                },
                {
                    "_class": "com.sonyericsson.rebuild.RebuildCause",
                    "shortDescription": "Rebuilds build #300",
                    "upstreamBuild": 300,
                    "upstreamProject": "sampleJobName",
                    "upstreamUrl": "view/ABCProjectView/job/sampleJobName/"
                }
            ]
        },
        {
            "_class": "hudson.model.ParametersAction",
            "parameters": [
                {
                    "_class": "hudson.model.StringParameterValue",
                    "name": "SNAPSHOTNAME",
                    "value": "ABCDE_12121.2000-2121212121212"
                },
                {
                    "_class": "hudson.model.StringParameterValue",
                    "name": "BUILD_LABEL",
                    "value": "ABCDE_12121.2000"
                }
            ]
        },
        {},
        {},
        {},
        {},
        {
            "_class": "hudson.plugins.parameterizedtrigger.BuildInfoExporterAction"
        },
        {},
        {},
        {},
        {}
    ],
    "artifacts": [],
    "building": false,
    "description": null,
    "displayName": "#301",
    "duration": 1199238,
    "estimatedDuration": 1194905,
    "executor": null,
    "fullDisplayName": "sampleJobName #301",
    "id": "301",
    "keepLog": false,
    "number": 301,
    "queueId": 189076,
    "result": "SUCCESS",
    "timestamp": 1583500786857,
    "url": "http://somedomainname:8080/job/sampleJobName/301/",
    "builtOn": "Server12345",
    "changeSet": {
        "_class": "hudson.scm.EmptyChangeLogSet",
        "items": [],
        "kind": null
    },
    "culprits": []
}

EDIT 1 : END

I have tried looking at several Stack Overflow issues, but still haven't been able to resolve it.

Please guide.

It's because you're not getting the actual JSON string, you're getting the toString() output on a groovyx.net.http.HttpResponseDecorator class.

You can see it printing it out here (it's easy to miss though... I missed it the first look 🙂):

 Json String :----   groovyx.net.http.HttpResponseDecorator@6b063470

I think you need to call jsonResponseObject.data to get the parsed data, and it might even return you a Map parsed form the JSON (so you can get rid of all your JSONObject code). Test it by changing to:

    def data = jsonResponseObject.data
    println "\n\n\n\n\n Json ${data.getClass().name} :----  $data" jsonResponseObject.toString()

If it is a java.util.Map, you can simplify your second part from:

    JSONParser jsonParser = new JSONParser();
    JSONObject jsonObject = (JSONObject) jsonParser.parse(jsonResponseObject.toString());

    JSONArray upstreamJobInfoArray = jsonObject.getJSONArray("causes");

    for (int i = 0; i < upstreamJobInfoArray.length(); i++) {
        JSONObject jobCauses = upstreamJobInfoArray.getJSONObject(i);
        String upstreamProjectName = jobCauses.getString("upstreamProject");
        println upstreamProjectName
    }

To (using data from above):

    data.actions.causes.upstreamProject.flatten().each { println it }