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Groovy makes HTTP and JSON unusually pleasant — once you know the patterns.

Quick HTTP GET

import groovy.json.JsonSlurper

def url = "https://api.github.com/repos/torvalds/linux"
def json = new JsonSlurper().parseText(new URL(url).text)
println json.name
println json.stargazers_count

The .text property of a URL makes the GET. JsonSlurper parses.

POST and other methods

import groovy.json.JsonOutput

def payload = JsonOutput.toJson([title: "hello", body: "world"])

def conn = new URL("https://example.com/api/posts").openConnection()
conn.setRequestMethod("POST")
conn.setRequestProperty("Content-Type", "application/json")
conn.setDoOutput(true)
conn.outputStream.withWriter { w -> w.write(payload) }

def response = conn.inputStream.text
println response

Verbose. For real HTTP work in Groovy, use libraries:

• HttpBuilder-NG — fluent DSL
• OkHttp (Java library, used directly)
• RESTEasy / Resttassured for testing

// HttpBuilder-NG style:
import static groovyx.net.http.HttpBuilder.configure

def result = configure {
    request.uri = 'https://api.example.com'
}.get {
    request.uri.path = '/users/42'
    response.parser('application/json') { config, fromServer ->
        new JsonSlurper().parse(fromServer.inputStream)
    }
}

JSON conversion

Object → JSON:

import groovy.json.JsonOutput

def data = [name: "Ada", scores: [80, 92, 75]]
def jsonStr = JsonOutput.toJson(data)
def pretty = JsonOutput.prettyPrint(jsonStr)

JSON → Map/List:

import groovy.json.JsonSlurper

def parsed = new JsonSlurper().parseText('{"name":"Ada","scores":[80,92,75]}')
parsed.name           // "Ada"
parsed.scores[0]      // 80

Groovy's parseText returns Maps and Lists — the most natural representation.

YAML, XML

• YAML: org.yaml.snakeyaml is the standard
• XML: XmlSlurper for namespace-aware parsing, XmlBuilder for generating

def xml = new XmlSlurper().parseText('''
<root>
    <user id="1">Ada</user>
    <user id="2">Bob</user>
</root>
''')

xml.user.each { u -> println "$u.@id: $u" }

Authentication

def url = new URL("https://api.example.com/private")
def auth = "Basic " + Base64.encoder.encodeToString("user:pass".bytes)
def conn = url.openConnection()
conn.setRequestProperty("Authorization", auth)
println conn.text

Error handling

Non-2xx HTTP responses throw IOException (the connection's input stream is closed). Wrap in try/catch:

try {
    def text = url.text
    process(text)
} catch (FileNotFoundException e) {
    // 404
} catch (IOException e) {
    // network error or 5xx
}

In Judge0 sandboxes, network access is usually disabled — these patterns work in real environments.