Dynamically build json using groovy

Question

I am trying to dynamically build some json based on data I retrieve from a database. Up until the opening '[' is the "root" I guess you could say. The next parts with name and value are dynamic and will be based on the number of results I get from the db. I query the db and then the idea was to iterate through the result adding to the json. Can I use jsonBuilder for the root section and then loop with jsonSlurper to add each additional section? Most of the examples I have seen deal with a root and then a one time "slurp" and then joining the two so wasn't sure if I should try a different method for looping and appending multiple sections.

Any tips would be greatly appreciated. Thanks.

    {
       "hostname": "$hostname",
       "path": "$path",
       "extPath": "$extPath",
       "appName": "$appName",
       "update": {"parameter":    [
                {
             "name": "$name",
             "value": "$value"
          },
                {
             "name": "$name",
             "value": "$value"
          }
       ]}
    }

EDIT: So what I ended up doing was just using StringBuilder to create the initial block and then append the subsequent sections. Maybe not the most graceful way to do it, but it works!

    //Create the json string
    StringBuilder json = new StringBuilder("""{
       "hostname": "$hostname",
       "path": "$path",
       "extPath": "$extPath",
       "appName": "$appName",
       "update": {"parameter":    ["""
    ) 


    //Append
    sql.eachRow("""<query>""",
    { params ->
    json.append("""{ "name": "params.name", "value": "params.value" },""");
    }
    ) 

    //Add closing json tags
    json.append("""]}}""")

sensei · Accepted Answer · 2016-10-28 16:19:41Z

2

If I got your explanation correctly and if the data is not very big (it can live in memory), I'd build a Map object (which is very easy to work with in groovy) and convert it to JSON afterwards. Something like this:

def data = [
    hostname: hostname,
    path: path,
    extPath: extPath,
    appName: appName,
    update: [parameter: []]
]

sql.eachRow(sqlStr) { row ->
  data.update.parameter << [name: row.name, value: row.value]
}

println JsonOutput.toJson(data)

answered Oct 28, 2016 at 16:19

sensei

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1 Comment

ssbsts Over a year ago

Thanks for the suggestion.

Magic Octopus Urn · Accepted Answer · 2016-10-28 17:45:22Z

If you're using Grails and Groovy you can utilize grails.converters.JSON.

First, define a JSON named config:

JSON.createNamedConfig('person') {
    it.registerObjectMarshaller(Person) {
        Person person ->
        def output = [:]
        output['name'] = person.name
        output['address'] = person.address
        output['age'] = person.age
        output
    }
}

This will result in a statically defined named configuration for the Object type of person. Now, you can simply call:

JSON.use('person') {
    Person.findAll() as JSON
}

This will return every person in the database with their name, address and age all in one JSON request. I don't know if you're using grails as well in this situation though, for pure Groovy go with another answer here.

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