Create JSON strings from Groovy variables in Jenkins Pipeline

Question

I have to create this JSON file in Groovy. I have try many things ( JsonOutput.toJson() / JsonSlurper.parseText() ) unsuccessfully.

{
   "attachments":[
      {
         "fallback":"New open task [Urgent]: <http://url_to_task|Test out Slack message attachments>",
         "pretext":"New open task [Urgent]: <http://url_to_task|Test out Slack message attachments>",
         "color":"#D00000",
         "fields":[
            {
               "title":"Notes",
               "value":"This is much easier than I thought it would be.",
               "short":false
            }
         ]
      }
   ]
}

This is for posting a Jenkins build message to Slack.

Answer 1

JSON is a format that uses human-readable text to transmit data objects consisting of attribute–value pairs and array data types. So, in general json is a formatted text.

In groovy json object is just a sequence of maps/arrays.

parsing json using JsonSlurperClassic

//use JsonSlurperClassic because it produces HashMap that could be serialized by pipeline
import groovy.json.JsonSlurperClassic

node{
    def json = readFile(file:'message2.json')
    def data = new JsonSlurperClassic().parseText(json)
    echo "color: ${data.attachments[0].color}"
}

parsing json using pipeline

node{
    def data = readJSON file:'message2.json'
    echo "color: ${data.attachments[0].color}"
}

building json from code and write it to file

import groovy.json.JsonOutput
node{
    //to create json declare a sequence of maps/arrays in groovy
    //here is the data according to your sample
    def data = [
        attachments:[
            [
                fallback: "New open task [Urgent]: <http://url_to_task|Test out Slack message attachments>",
                pretext : "New open task [Urgent]: <http://url_to_task|Test out Slack message attachments>",
                color   : "#D00000",
                fields  :[
                    [
                        title: "Notes",
                        value: "This is much easier than I thought it would be.",
                        short: false
                    ]
                ]
            ]
        ]
    ]
    //two alternatives to write

    //native pipeline step:
    writeJSON(file: 'message1.json', json: data)

    //but if writeJSON not supported by your version:
    //convert maps/arrays to json formatted string
    def json = JsonOutput.toJson(data)
    //if you need pretty print (multiline) json
    json = JsonOutput.prettyPrint(json)

    //put string into the file:
    writeFile(file:'message2.json', text: json)

}

Answer 2

Found this question while I was trying to do something (I believed) should be simple to do, but wasn't addressed by the other answer. If you already have the JSON loaded as a string inside a variable, how do you convert it to a native object? Obviously you could do new JsonSlurperClassic().parseText(json) as the other answer suggests, but there is a native way in Jenkins to do this:

node () {
  def myJson = '{"version":"1.0.0"}';
  def myObject = readJSON text: myJson;
  echo myObject.version;
}

Hope this helps someone.

Edit: As explained in the comments "native" isn't quite accurate.

Answer 3

If you are stucked on an installation using sandboxes and Jenkins Script Security plugin with no possibility to add whitelisted classes/methods, the only way I found is the following :

def slackSendOnRestrictedContext(params) {

    if (params.attachments != null) {
        /* Soooo ugly but no other choice with restrictions of
           Jenkins Script Pipeline Security plugin ^^ */
        def paramsAsJson = JsonOutput.toJson(params)
        def paramsAsJsonFromReadJson = readJSON text: paramsAsJson
        params.attachments = paramsAsJsonFromReadJson.attachments.toString()
    }

    slackSend (params)
}

Answer 4

This will return value of the "version" from the jsonFile file:

def getVersion(jsonFile){

  def fileContent = readFile "${jsonFile}"
  Map jsonContent = (Map) new JsonSlurper().parseText(fileContent)
  version = jsonContent.get("version")

  return version

}