如何使用groovy在mongodb集合中的字段中存储变量中的值？

import com.mongodb.MongoClient
import com.mongodb.MongoCredential
import com.mongodb.ServerAddress
import com.mongodb.client.MongoDatabase
import com.mongodb.client.MongoCollection
import org.bson.Document

def serverAddress = new ServerAddress("mongodb://localhost:27017")
def credential = MongoCredential.createCredential("username", "database", "password".toCharArray())
def mongoClient = new MongoClient(serverAddress, [credential] as List<MongoCredential>)
def database = mongoClient.getDatabase("database")
def collection = database.getCollection("collection")

def variableValue = "Hello, World!"

def document = new Document("variable", variableValue)

collection.insertOne(document)

mongoClient.close()